diff --git a/.github/workflows/CICD.yml b/.github/workflows/CICD.yml
index 9fd08b26f..8a1e142df 100644
--- a/.github/workflows/CICD.yml
+++ b/.github/workflows/CICD.yml
@@ -13,8 +13,8 @@ env:
   PROJECT_NAME: coreutils
   PROJECT_DESC: "Core universal (cross-platform) utilities"
   PROJECT_AUTH: "uutils"
-  RUST_MIN_SRV: "1.51.0" ## MSRV v1.51.0
-  RUST_COV_SRV: "2020-08-01" ## (~v1.47.0) supported rust version for code coverage; (date required/used by 'coverage') ## !maint: refactor when code coverage support is included in the stable channel
+  RUST_MIN_SRV: "1.47.0" ## MSRV v1.47.0
+  RUST_COV_SRV: "2021-05-06" ## (~v1.52.0) supported rust version for code coverage; (date required/used by 'coverage') ## !maint: refactor when code coverage support is included in the stable channel
 
 on: [push, pull_request]
 
diff --git a/.vscode/cspell.dictionaries/people.wordlist.txt b/.vscode/cspell.dictionaries/people.wordlist.txt
index d7665585b..405733836 100644
--- a/.vscode/cspell.dictionaries/people.wordlist.txt
+++ b/.vscode/cspell.dictionaries/people.wordlist.txt
@@ -151,6 +151,9 @@ Sylvestre Ledru
 T Jameson Little
     Jameson
     Little
+Thomas Queiroz
+    Thomas
+    Queiroz
 Tobias Bohumir Schottdorf
     Tobias
     Bohumir
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 1cb9b333a..2a8a80315 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -4,9 +4,10 @@ Contributions are very welcome, and should target Rust's master branch until the
 standard libraries are stabilized. You may *claim* an item on the to-do list by
 following these steps:
 
-1. Open an issue named "Implement [the utility of your choice]", e.g. "Implement ls"
+1. Open an issue named "Implement [the utility of your choice]", e.g. "Implement
+   ls".
 1. State that you are working on this utility.
-1. Develop the utility
+1. Develop the utility.
 1. Add integration tests.
 1. Add the reference to your utility into Cargo.toml and Makefile.
 1. Remove utility from the to-do list in the README.
@@ -17,12 +18,20 @@ search the issues to make sure no one else is working on it.
 
 ## Best practices
 
-1. Follow what GNU is doing in term of options and behavior.
-1. If possible, look at the GNU test suite execution in the CI and make the test work if failing.
+1. Follow what GNU is doing in terms of options and behavior. It is recommended
+   to look at the GNU Coreutils manual ([on the
+   web](https://www.gnu.org/software/coreutils/manual/html_node/index.html), or
+   locally using `info <utility>`). It is more in depth than the man pages and
+   provides a good description of available features and their implementation
+   details.
+1. If possible, look at the GNU test suite execution in the CI and make the test
+   work if failing.
 1. Use clap for argument management.
-1. Make sure that the code coverage is covering all of the cases, including errors.     
+1. Make sure that the code coverage is covering all of the cases, including
+   errors.
 1. The code must be clippy-warning-free and rustfmt-compliant.
-1. Don't hesitate to move common functions into uucore if they can be reused by other binaries.
+1. Don't hesitate to move common functions into uucore if they can be reused by
+   other binaries.
 1. Unsafe code should be documented with Safety comments.
 1. uutils is original code. It cannot contain code from existing GNU or Unix-like
    utilities, nor should it link to or reference GNU libraries.
@@ -99,9 +108,11 @@ project, a tool like `cargo-license` can be used to show their license details.
 The following types of license are acceptable:
 
 * MIT License
-* Dual- or tri-license with an MIT License option ("Apache-2.0 or MIT" is a popular combination)
+* Dual- or tri-license with an MIT License option ("Apache-2.0 or MIT" is a
+  popular combination)
 * "MIT equivalent" license (2-clause BSD, 3-clause BSD, ISC)
 * License less restrictive than the MIT License (CC0 1.0 Universal)
+* Apache License version 2.0
 
 Licenses we will not use:
 
diff --git a/Cargo.lock b/Cargo.lock
index d3b0058f6..1803a9c33 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,5 +1,7 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+version = 3
+
 [[package]]
 name = "Inflector"
 version = "0.11.4"
@@ -2714,6 +2716,7 @@ version = "0.0.7"
 dependencies = [
  "clap",
  "libc",
+ "nix 0.20.0",
  "redox_syscall 0.1.57",
  "uucore",
  "uucore_procs",
@@ -2917,6 +2920,7 @@ dependencies = [
 name = "uucore"
 version = "0.0.9"
 dependencies = [
+ "clap",
  "data-encoding",
  "dns-lookup",
  "dunce",
diff --git a/src/uu/arch/src/arch.rs b/src/uu/arch/src/arch.rs
index ef12eb82a..94ec97e98 100644
--- a/src/uu/arch/src/arch.rs
+++ b/src/uu/arch/src/arch.rs
@@ -6,9 +6,6 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 
-// clippy bug https://github.com/rust-lang/rust-clippy/issues/7422
-#![allow(clippy::nonstandard_macro_braces)]
-
 #[macro_use]
 extern crate uucore;
 
diff --git a/src/uu/cat/src/cat.rs b/src/uu/cat/src/cat.rs
index 8ad563c5d..35a5308ed 100644
--- a/src/uu/cat/src/cat.rs
+++ b/src/uu/cat/src/cat.rs
@@ -10,9 +10,6 @@
 
 // spell-checker:ignore (ToDO) nonprint nonblank nonprinting
 
-// clippy bug https://github.com/rust-lang/rust-clippy/issues/7422
-#![allow(clippy::nonstandard_macro_braces)]
-
 #[cfg(unix)]
 extern crate unix_socket;
 #[macro_use]
diff --git a/src/uu/chown/src/chown.rs b/src/uu/chown/src/chown.rs
index e1d3ff22b..081d3a148 100644
--- a/src/uu/chown/src/chown.rs
+++ b/src/uu/chown/src/chown.rs
@@ -14,6 +14,8 @@ use uucore::fs::resolve_relative_path;
 use uucore::libc::{gid_t, uid_t};
 use uucore::perms::{wrap_chown, Verbosity};
 
+use uucore::error::{FromIo, UError, UResult, USimpleError};
+
 use clap::{crate_version, App, Arg};
 
 use walkdir::WalkDir;
@@ -66,7 +68,8 @@ fn get_usage() -> String {
     )
 }
 
-pub fn uumain(args: impl uucore::Args) -> i32 {
+#[uucore_procs::gen_uumain]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let args = args
         .collect_str(InvalidEncodingHandling::Ignore)
         .accept_any();
@@ -104,8 +107,10 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
     if recursive {
         if bit_flag == FTS_PHYSICAL {
             if derefer == 1 {
-                show_error!("-R --dereference requires -H or -L");
-                return 1;
+                return Err(USimpleError::new(
+                    1,
+                    "-R --dereference requires -H or -L".to_string(),
+                ));
             }
             derefer = 0;
         }
@@ -126,15 +131,11 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
     };
 
     let filter = if let Some(spec) = matches.value_of(options::FROM) {
-        match parse_spec(spec) {
-            Ok((Some(uid), None)) => IfFrom::User(uid),
-            Ok((None, Some(gid))) => IfFrom::Group(gid),
-            Ok((Some(uid), Some(gid))) => IfFrom::UserGroup(uid, gid),
-            Ok((None, None)) => IfFrom::All,
-            Err(e) => {
-                show_error!("{}", e);
-                return 1;
-            }
+        match parse_spec(spec)? {
+            (Some(uid), None) => IfFrom::User(uid),
+            (None, Some(gid)) => IfFrom::Group(gid),
+            (Some(uid), Some(gid)) => IfFrom::UserGroup(uid, gid),
+            (None, None) => IfFrom::All,
         }
     } else {
         IfFrom::All
@@ -143,27 +144,14 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
     let dest_uid: Option<u32>;
     let dest_gid: Option<u32>;
     if let Some(file) = matches.value_of(options::REFERENCE) {
-        match fs::metadata(&file) {
-            Ok(meta) => {
-                dest_gid = Some(meta.gid());
-                dest_uid = Some(meta.uid());
-            }
-            Err(e) => {
-                show_error!("failed to get attributes of '{}': {}", file, e);
-                return 1;
-            }
-        }
+        let meta = fs::metadata(&file)
+            .map_err_context(|| format!("failed to get attributes of '{}'", file))?;
+        dest_gid = Some(meta.gid());
+        dest_uid = Some(meta.uid());
     } else {
-        match parse_spec(owner) {
-            Ok((u, g)) => {
-                dest_uid = u;
-                dest_gid = g;
-            }
-            Err(e) => {
-                show_error!("{}", e);
-                return 1;
-            }
-        }
+        let (u, g) = parse_spec(owner)?;
+        dest_uid = u;
+        dest_gid = g;
     }
     let executor = Chowner {
         bit_flag,
@@ -275,7 +263,7 @@ pub fn uu_app() -> App<'static, 'static> {
         )
 }
 
-fn parse_spec(spec: &str) -> Result<(Option<u32>, Option<u32>), String> {
+fn parse_spec(spec: &str) -> UResult<(Option<u32>, Option<u32>)> {
     let args = spec.split_terminator(':').collect::<Vec<_>>();
     let usr_only = args.len() == 1 && !args[0].is_empty();
     let grp_only = args.len() == 2 && args[0].is_empty();
@@ -283,7 +271,7 @@ fn parse_spec(spec: &str) -> Result<(Option<u32>, Option<u32>), String> {
     let uid = if usr_only || usr_grp {
         Some(
             Passwd::locate(args[0])
-                .map_err(|_| format!("invalid user: '{}'", spec))?
+                .map_err(|_| USimpleError::new(1, format!("invalid user: '{}'", spec)))?
                 .uid(),
         )
     } else {
@@ -292,7 +280,7 @@ fn parse_spec(spec: &str) -> Result<(Option<u32>, Option<u32>), String> {
     let gid = if grp_only || usr_grp {
         Some(
             Group::locate(args[1])
-                .map_err(|_| format!("invalid group: '{}'", spec))?
+                .map_err(|_| USimpleError::new(1, format!("invalid group: '{}'", spec)))?
                 .gid(),
         )
     } else {
@@ -330,12 +318,15 @@ macro_rules! unwrap {
 }
 
 impl Chowner {
-    fn exec(&self) -> i32 {
+    fn exec(&self) -> UResult<()> {
         let mut ret = 0;
         for f in &self.files {
             ret |= self.traverse(f);
         }
-        ret
+        if ret != 0 {
+            return Err(UError::from(ret));
+        }
+        Ok(())
     }
 
     fn traverse<P: AsRef<Path>>(&self, root: P) -> i32 {
diff --git a/src/uu/cp/src/cp.rs b/src/uu/cp/src/cp.rs
index 4deaefa98..7c67649c2 100644
--- a/src/uu/cp/src/cp.rs
+++ b/src/uu/cp/src/cp.rs
@@ -55,7 +55,6 @@ use walkdir::WalkDir;
 use std::os::unix::fs::PermissionsExt;
 
 #[cfg(target_os = "linux")]
-#[allow(clippy::missing_safety_doc)]
 ioctl!(write ficlone with 0x94, 9; std::os::raw::c_int);
 
 quick_error! {
@@ -98,6 +97,9 @@ quick_error! {
         /// path, but those that are not implemented yet should return
         /// a NotImplemented error.
         NotImplemented(opt: String) { display("Option '{}' not yet implemented.", opt) }
+
+        /// Invalid arguments to backup
+        Backup(description: String) { display("{}\nTry 'cp --help' for more information.", description) }
     }
 }
 
@@ -359,7 +361,6 @@ pub fn uu_app() -> App<'static, 'static> {
              .takes_value(true)
              .require_equals(true)
              .min_values(0)
-             .possible_values(backup_control::BACKUP_CONTROL_VALUES)
              .value_name("CONTROL")
         )
         .arg(Arg::with_name(options::BACKUP_NO_ARG)
@@ -604,9 +605,17 @@ impl Options {
             || matches.is_present(options::ARCHIVE);
 
         let backup_mode = backup_control::determine_backup_mode(
-            matches.is_present(options::BACKUP_NO_ARG) || matches.is_present(options::BACKUP),
+            matches.is_present(options::BACKUP_NO_ARG),
+            matches.is_present(options::BACKUP),
             matches.value_of(options::BACKUP),
         );
+        let backup_mode = match backup_mode {
+            Err(err) => {
+                return Err(Error::Backup(err));
+            }
+            Ok(mode) => mode,
+        };
+
         let backup_suffix =
             backup_control::determine_backup_suffix(matches.value_of(options::SUFFIX));
 
diff --git a/src/uu/csplit/src/csplit_error.rs b/src/uu/csplit/src/csplit_error.rs
index e2f514ea9..637cf8890 100644
--- a/src/uu/csplit/src/csplit_error.rs
+++ b/src/uu/csplit/src/csplit_error.rs
@@ -1,6 +1,3 @@
-// clippy bug https://github.com/rust-lang/rust-clippy/issues/7422
-#![allow(clippy::nonstandard_macro_braces)]
-
 use std::io;
 use thiserror::Error;
 
diff --git a/src/uu/df/src/df.rs b/src/uu/df/src/df.rs
index 1092938df..baa5fe292 100644
--- a/src/uu/df/src/df.rs
+++ b/src/uu/df/src/df.rs
@@ -8,6 +8,8 @@
 
 #[macro_use]
 extern crate uucore;
+use uucore::error::UCustomError;
+use uucore::error::UResult;
 #[cfg(unix)]
 use uucore::fsext::statfs_fn;
 use uucore::fsext::{read_fs_list, FsUsage, MountInfo};
@@ -19,8 +21,10 @@ use std::cell::Cell;
 use std::collections::HashMap;
 use std::collections::HashSet;
 
+use std::error::Error;
 #[cfg(unix)]
 use std::ffi::CString;
+use std::fmt::Display;
 #[cfg(unix)]
 use std::mem;
 
@@ -33,9 +37,6 @@ use std::path::Path;
 static ABOUT: &str = "Show information about the file system on which each FILE resides,\n\
                       or all file systems by default.";
 
-static EXIT_OK: i32 = 0;
-static EXIT_ERR: i32 = 1;
-
 static OPT_ALL: &str = "all";
 static OPT_BLOCKSIZE: &str = "blocksize";
 static OPT_DIRECT: &str = "direct";
@@ -226,8 +227,8 @@ fn filter_mount_list(vmi: Vec<MountInfo>, paths: &[String], opt: &Options) -> Ve
 /// Convert `value` to a human readable string based on `base`.
 /// e.g. It returns 1G when value is 1 * 1024 * 1024 * 1024 and base is 1024.
 /// Note: It returns `value` if `base` isn't positive.
-fn human_readable(value: u64, base: i64) -> String {
-    match base {
+fn human_readable(value: u64, base: i64) -> UResult<String> {
+    let base_str = match base {
         d if d < 0 => value.to_string(),
 
         // ref: [Binary prefix](https://en.wikipedia.org/wiki/Binary_prefix) @@ <https://archive.is/cnwmF>
@@ -242,8 +243,10 @@ fn human_readable(value: u64, base: i64) -> String {
             NumberPrefix::Prefixed(prefix, bytes) => format!("{:.1}{}", bytes, prefix.symbol()),
         },
 
-        _ => crash!(EXIT_ERR, "Internal error: Unknown base value {}", base),
-    }
+        _ => return Err(DfError::InvalidBaseValue(base.to_string()).into()),
+    };
+
+    Ok(base_str)
 }
 
 fn use_size(free_size: u64, total_size: u64) -> String {
@@ -256,7 +259,31 @@ fn use_size(free_size: u64, total_size: u64) -> String {
     );
 }
 
-pub fn uumain(args: impl uucore::Args) -> i32 {
+#[derive(Debug)]
+enum DfError {
+    InvalidBaseValue(String),
+}
+
+impl Display for DfError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            DfError::InvalidBaseValue(s) => write!(f, "Internal error: Unknown base value {}", s),
+        }
+    }
+}
+
+impl Error for DfError {}
+
+impl UCustomError for DfError {
+    fn code(&self) -> i32 {
+        match self {
+            DfError::InvalidBaseValue(_) => 1,
+        }
+    }
+}
+
+#[uucore_procs::gen_uumain]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let usage = get_usage();
     let matches = uu_app().usage(&usage[..]).get_matches_from(args);
 
@@ -269,7 +296,7 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
     {
         if matches.is_present(OPT_INODES) {
             println!("{}: doesn't support -i option", executable!());
-            return EXIT_OK;
+            return Ok(());
         }
     }
 
@@ -353,15 +380,15 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
         if opt.show_inode_instead {
             print!(
                 "{0: >12} ",
-                human_readable(fs.usage.files, opt.human_readable_base)
+                human_readable(fs.usage.files, opt.human_readable_base)?
             );
             print!(
                 "{0: >12} ",
-                human_readable(fs.usage.files - fs.usage.ffree, opt.human_readable_base)
+                human_readable(fs.usage.files - fs.usage.ffree, opt.human_readable_base)?
             );
             print!(
                 "{0: >12} ",
-                human_readable(fs.usage.ffree, opt.human_readable_base)
+                human_readable(fs.usage.ffree, opt.human_readable_base)?
             );
             print!(
                 "{0: >5} ",
@@ -375,15 +402,15 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
             let free_size = fs.usage.blocksize * fs.usage.bfree;
             print!(
                 "{0: >12} ",
-                human_readable(total_size, opt.human_readable_base)
+                human_readable(total_size, opt.human_readable_base)?
             );
             print!(
                 "{0: >12} ",
-                human_readable(total_size - free_size, opt.human_readable_base)
+                human_readable(total_size - free_size, opt.human_readable_base)?
             );
             print!(
                 "{0: >12} ",
-                human_readable(free_size, opt.human_readable_base)
+                human_readable(free_size, opt.human_readable_base)?
             );
             if cfg!(target_os = "macos") {
                 let used = fs.usage.blocks - fs.usage.bfree;
@@ -396,7 +423,7 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
         println!();
     }
 
-    EXIT_OK
+    Ok(())
 }
 
 pub fn uu_app() -> App<'static, 'static> {
diff --git a/src/uu/dirname/src/dirname.rs b/src/uu/dirname/src/dirname.rs
index 8d85dc85e..63ee57272 100644
--- a/src/uu/dirname/src/dirname.rs
+++ b/src/uu/dirname/src/dirname.rs
@@ -5,9 +5,6 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 
-// Clippy bug: https://github.com/rust-lang/rust-clippy/issues/7422
-#![allow(clippy::nonstandard_macro_braces)]
-
 #[macro_use]
 extern crate uucore;
 
diff --git a/src/uu/du/src/du.rs b/src/uu/du/src/du.rs
index 61a3b8c29..9c05eb982 100644
--- a/src/uu/du/src/du.rs
+++ b/src/uu/du/src/du.rs
@@ -5,9 +5,6 @@
 //  * For the full copyright and license information, please view the LICENSE
 //  * file that was distributed with this source code.
 
-// Clippy bug: https://github.com/rust-lang/rust-clippy/issues/7422
-#![allow(clippy::nonstandard_macro_braces)]
-
 #[macro_use]
 extern crate uucore;
 
diff --git a/src/uu/echo/src/echo.rs b/src/uu/echo/src/echo.rs
index 8c976c2b4..aae1ad10d 100644
--- a/src/uu/echo/src/echo.rs
+++ b/src/uu/echo/src/echo.rs
@@ -13,6 +13,7 @@ use clap::{crate_version, App, Arg};
 use std::io::{self, Write};
 use std::iter::Peekable;
 use std::str::Chars;
+use uucore::error::{FromIo, UResult};
 use uucore::InvalidEncodingHandling;
 
 const NAME: &str = "echo";
@@ -113,7 +114,8 @@ fn print_escaped(input: &str, mut output: impl Write) -> io::Result<bool> {
     Ok(should_stop)
 }
 
-pub fn uumain(args: impl uucore::Args) -> i32 {
+#[uucore_procs::gen_uumain]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let args = args
         .collect_str(InvalidEncodingHandling::ConvertLossy)
         .accept_any();
@@ -126,13 +128,7 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
         None => vec!["".to_string()],
     };
 
-    match execute(no_newline, escaped, values) {
-        Ok(_) => 0,
-        Err(f) => {
-            show_error!("{}", f);
-            1
-        }
-    }
+    execute(no_newline, escaped, values).map_err_context(|| "could not write to stdout".to_string())
 }
 
 pub fn uu_app() -> App<'static, 'static> {
diff --git a/src/uu/expand/src/expand.rs b/src/uu/expand/src/expand.rs
index 66c3eb259..d5c37ce21 100644
--- a/src/uu/expand/src/expand.rs
+++ b/src/uu/expand/src/expand.rs
@@ -36,28 +36,86 @@ fn get_usage() -> String {
     format!("{0} [OPTION]... [FILE]...", executable!())
 }
 
-fn tabstops_parse(s: String) -> Vec<usize> {
-    let words = s.split(',');
+/// The mode to use when replacing tabs beyond the last one specified in
+/// the `--tabs` argument.
+enum RemainingMode {
+    None,
+    Slash,
+    Plus,
+}
 
-    let nums = words
-        .map(|sn| {
-            sn.parse::<usize>()
-                .unwrap_or_else(|_| crash!(1, "{}\n", "tab size contains invalid character(s)"))
-        })
-        .collect::<Vec<usize>>();
+/// Decide whether the character is either a space or a comma.
+///
+/// # Examples
+///
+/// ```rust,ignore
+/// assert!(is_space_or_comma(' '))
+/// assert!(is_space_or_comma(','))
+/// assert!(!is_space_or_comma('a'))
+/// ```
+fn is_space_or_comma(c: char) -> bool {
+    c == ' ' || c == ','
+}
 
-    if nums.iter().any(|&n| n == 0) {
-        crash!(1, "{}\n", "tab size cannot be 0");
+/// Parse a list of tabstops from a `--tabs` argument.
+///
+/// This function returns both the vector of numbers appearing in the
+/// comma- or space-separated list, and also an optional mode, specified
+/// by either a "/" or a "+" character appearing before the final number
+/// in the list. This mode defines the strategy to use for computing the
+/// number of spaces to use for columns beyond the end of the tab stop
+/// list specified here.
+fn tabstops_parse(s: String) -> (RemainingMode, Vec<usize>) {
+    // Leading commas and spaces are ignored.
+    let s = s.trim_start_matches(is_space_or_comma);
+
+    // If there were only commas and spaces in the string, just use the
+    // default tabstops.
+    if s.is_empty() {
+        return (RemainingMode::None, vec![DEFAULT_TABSTOP]);
     }
 
-    if let (false, _) = nums
-        .iter()
-        .fold((true, 0), |(acc, last), &n| (acc && last <= n, n))
-    {
-        crash!(1, "{}\n", "tab sizes must be ascending");
-    }
+    let mut nums = vec![];
+    let mut remaining_mode = RemainingMode::None;
+    for word in s.split(is_space_or_comma) {
+        let bytes = word.as_bytes();
+        for i in 0..bytes.len() {
+            match bytes[i] {
+                b'+' => {
+                    remaining_mode = RemainingMode::Plus;
+                }
+                b'/' => {
+                    remaining_mode = RemainingMode::Slash;
+                }
+                _ => {
+                    // Parse a number from the byte sequence.
+                    let num = from_utf8(&bytes[i..]).unwrap().parse::<usize>().unwrap();
 
-    nums
+                    // Tab size must be positive.
+                    if num == 0 {
+                        crash!(1, "{}\n", "tab size cannot be 0");
+                    }
+
+                    // Tab sizes must be ascending.
+                    if let Some(last_stop) = nums.last() {
+                        if *last_stop >= num {
+                            crash!(1, "tab sizes must be ascending");
+                        }
+                    }
+
+                    // Append this tab stop to the list of all tabstops.
+                    nums.push(num);
+                    break;
+                }
+            }
+        }
+    }
+    // If no numbers could be parsed (for example, if `s` were "+,+,+"),
+    // then just use the default tabstops.
+    if nums.is_empty() {
+        nums = vec![DEFAULT_TABSTOP];
+    }
+    (remaining_mode, nums)
 }
 
 struct Options {
@@ -66,13 +124,17 @@ struct Options {
     tspaces: String,
     iflag: bool,
     uflag: bool,
+
+    /// Strategy for expanding tabs for columns beyond those specified
+    /// in `tabstops`.
+    remaining_mode: RemainingMode,
 }
 
 impl Options {
     fn new(matches: &ArgMatches) -> Options {
-        let tabstops = match matches.value_of(options::TABS) {
+        let (remaining_mode, tabstops) = match matches.value_of(options::TABS) {
             Some(s) => tabstops_parse(s.to_string()),
-            None => vec![DEFAULT_TABSTOP],
+            None => (RemainingMode::None, vec![DEFAULT_TABSTOP]),
         };
 
         let iflag = matches.is_present(options::INITIAL);
@@ -102,6 +164,7 @@ impl Options {
             tspaces,
             iflag,
             uflag,
+            remaining_mode,
         }
     }
 }
@@ -159,13 +222,41 @@ fn open(path: String) -> BufReader<Box<dyn Read + 'static>> {
     }
 }
 
-fn next_tabstop(tabstops: &[usize], col: usize) -> usize {
-    if tabstops.len() == 1 {
-        tabstops[0] - col % tabstops[0]
-    } else {
-        match tabstops.iter().find(|&&t| t > col) {
+/// Compute the number of spaces to the next tabstop.
+///
+/// `tabstops` is the sequence of tabstop locations.
+///
+/// `col` is the index of the current cursor in the line being written.
+///
+/// If `remaining_mode` is [`RemainingMode::Plus`], then the last entry
+/// in the `tabstops` slice is interpreted as a relative number of
+/// spaces, which this function will return for every input value of
+/// `col` beyond the end of the second-to-last element of `tabstops`.
+///
+/// If `remaining_mode` is [`RemainingMode::Plus`], then the last entry
+/// in the `tabstops` slice is interpreted as a relative number of
+/// spaces, which this function will return for every input value of
+/// `col` beyond the end of the second-to-last element of `tabstops`.
+fn next_tabstop(tabstops: &[usize], col: usize, remaining_mode: &RemainingMode) -> usize {
+    let num_tabstops = tabstops.len();
+    match remaining_mode {
+        RemainingMode::Plus => match tabstops[0..num_tabstops - 1].iter().find(|&&t| t > col) {
             Some(t) => t - col,
-            None => 1,
+            None => tabstops[num_tabstops - 1] - 1,
+        },
+        RemainingMode::Slash => match tabstops[0..num_tabstops - 1].iter().find(|&&t| t > col) {
+            Some(t) => t - col,
+            None => tabstops[num_tabstops - 1] - col % tabstops[num_tabstops - 1],
+        },
+        RemainingMode::None => {
+            if num_tabstops == 1 {
+                tabstops[0] - col % tabstops[0]
+            } else {
+                match tabstops.iter().find(|&&t| t > col) {
+                    Some(t) => t - col,
+                    None => 1,
+                }
+            }
         }
     }
 }
@@ -232,12 +323,16 @@ fn expand(options: Options) {
                 match ctype {
                     Tab => {
                         // figure out how many spaces to the next tabstop
-                        let nts = next_tabstop(ts, col);
+                        let nts = next_tabstop(ts, col, &options.remaining_mode);
                         col += nts;
 
                         // now dump out either spaces if we're expanding, or a literal tab if we're not
                         if init || !options.iflag {
-                            safe_unwrap!(output.write_all(options.tspaces[..nts].as_bytes()));
+                            if nts <= options.tspaces.len() {
+                                safe_unwrap!(output.write_all(options.tspaces[..nts].as_bytes()));
+                            } else {
+                                safe_unwrap!(output.write_all(" ".repeat(nts).as_bytes()));
+                            };
                         } else {
                             safe_unwrap!(output.write_all(&buf[byte..byte + nbytes]));
                         }
@@ -269,3 +364,30 @@ fn expand(options: Options) {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::next_tabstop;
+    use super::RemainingMode;
+
+    #[test]
+    fn test_next_tabstop_remaining_mode_none() {
+        assert_eq!(next_tabstop(&[1, 5], 0, &RemainingMode::None), 1);
+        assert_eq!(next_tabstop(&[1, 5], 3, &RemainingMode::None), 2);
+        assert_eq!(next_tabstop(&[1, 5], 6, &RemainingMode::None), 1);
+    }
+
+    #[test]
+    fn test_next_tabstop_remaining_mode_plus() {
+        assert_eq!(next_tabstop(&[1, 5], 0, &RemainingMode::Plus), 1);
+        assert_eq!(next_tabstop(&[1, 5], 3, &RemainingMode::Plus), 4);
+        assert_eq!(next_tabstop(&[1, 5], 6, &RemainingMode::Plus), 4);
+    }
+
+    #[test]
+    fn test_next_tabstop_remaining_mode_slash() {
+        assert_eq!(next_tabstop(&[1, 5], 0, &RemainingMode::Slash), 1);
+        assert_eq!(next_tabstop(&[1, 5], 3, &RemainingMode::Slash), 2);
+        assert_eq!(next_tabstop(&[1, 5], 6, &RemainingMode::Slash), 4);
+    }
+}
diff --git a/src/uu/false/src/false.rs b/src/uu/false/src/false.rs
index 17c681129..2d64c8376 100644
--- a/src/uu/false/src/false.rs
+++ b/src/uu/false/src/false.rs
@@ -5,12 +5,17 @@
 //  * For the full copyright and license information, please view the LICENSE
 //  * file that was distributed with this source code.
 
+#[macro_use]
+extern crate uucore;
+
 use clap::App;
+use uucore::error::{UError, UResult};
 use uucore::executable;
 
-pub fn uumain(args: impl uucore::Args) -> i32 {
+#[uucore_procs::gen_uumain]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     uu_app().get_matches_from(args);
-    1
+    Err(UError::from(1))
 }
 
 pub fn uu_app() -> App<'static, 'static> {
diff --git a/src/uu/hostid/src/hostid.rs b/src/uu/hostid/src/hostid.rs
index 180c4d2e5..b0f68968d 100644
--- a/src/uu/hostid/src/hostid.rs
+++ b/src/uu/hostid/src/hostid.rs
@@ -7,9 +7,6 @@
 
 // spell-checker:ignore (ToDO) gethostid
 
-// Clippy bug: https://github.com/rust-lang/rust-clippy/issues/7422
-#![allow(clippy::nonstandard_macro_braces)]
-
 #[macro_use]
 extern crate uucore;
 
diff --git a/src/uu/hostname/src/hostname.rs b/src/uu/hostname/src/hostname.rs
index 14f8b9df2..045e43045 100644
--- a/src/uu/hostname/src/hostname.rs
+++ b/src/uu/hostname/src/hostname.rs
@@ -7,9 +7,6 @@
 
 // spell-checker:ignore (ToDO) MAKEWORD addrs hashset
 
-// Clippy bug: https://github.com/rust-lang/rust-clippy/issues/7422
-#![allow(clippy::nonstandard_macro_braces)]
-
 #[macro_use]
 extern crate uucore;
 
diff --git a/src/uu/install/src/install.rs b/src/uu/install/src/install.rs
index bd227da56..81d44bb6c 100644
--- a/src/uu/install/src/install.rs
+++ b/src/uu/install/src/install.rs
@@ -308,15 +308,25 @@ fn behavior(matches: &ArgMatches) -> Result<Behavior, i32> {
         None
     };
 
+    let backup_mode = backup_control::determine_backup_mode(
+        matches.is_present(OPT_BACKUP_NO_ARG),
+        matches.is_present(OPT_BACKUP),
+        matches.value_of(OPT_BACKUP),
+    );
+    let backup_mode = match backup_mode {
+        Err(err) => {
+            show_usage_error!("{}", err);
+            return Err(1);
+        }
+        Ok(mode) => mode,
+    };
+
     let target_dir = matches.value_of(OPT_TARGET_DIRECTORY).map(|d| d.to_owned());
 
     Ok(Behavior {
         main_function,
         specified_mode,
-        backup_mode: backup_control::determine_backup_mode(
-            matches.is_present(OPT_BACKUP_NO_ARG) || matches.is_present(OPT_BACKUP),
-            matches.value_of(OPT_BACKUP),
-        ),
+        backup_mode,
         suffix: backup_control::determine_backup_suffix(matches.value_of(OPT_SUFFIX)),
         owner: matches.value_of(OPT_OWNER).unwrap_or("").to_string(),
         group: matches.value_of(OPT_GROUP).unwrap_or("").to_string(),
diff --git a/src/uu/kill/src/kill.rs b/src/uu/kill/src/kill.rs
index 92868efdb..b3f5010ca 100644
--- a/src/uu/kill/src/kill.rs
+++ b/src/uu/kill/src/kill.rs
@@ -13,14 +13,12 @@ extern crate uucore;
 use clap::{crate_version, App, Arg};
 use libc::{c_int, pid_t};
 use std::io::Error;
+use uucore::error::{UResult, USimpleError};
 use uucore::signals::ALL_SIGNALS;
 use uucore::InvalidEncodingHandling;
 
 static ABOUT: &str = "Send signal to processes or list information about signals.";
 
-static EXIT_OK: i32 = 0;
-static EXIT_ERR: i32 = 1;
-
 pub mod options {
     pub static PIDS_OR_SIGNALS: &str = "pids_of_signals";
     pub static LIST: &str = "list";
@@ -36,7 +34,8 @@ pub enum Mode {
     List,
 }
 
-pub fn uumain(args: impl uucore::Args) -> i32 {
+#[uucore_procs::gen_uumain]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let args = args
         .collect_str(InvalidEncodingHandling::Ignore)
         .accept_any();
@@ -66,13 +65,14 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
                 (None, Some(s)) => s.to_owned(),
                 (None, None) => "TERM".to_owned(),
             };
-            return kill(&sig, &pids_or_signals);
+            kill(&sig, &pids_or_signals)
+        }
+        Mode::Table => {
+            table();
+            Ok(())
         }
-        Mode::Table => table(),
         Mode::List => list(pids_or_signals.get(0).cloned()),
     }
-
-    EXIT_OK
 }
 
 pub fn uu_app() -> App<'static, 'static> {
@@ -139,20 +139,23 @@ fn table() {
             println!();
         }
     }
-    println!()
+    println!();
 }
 
-fn print_signal(signal_name_or_value: &str) {
+fn print_signal(signal_name_or_value: &str) -> UResult<()> {
     for (value, &signal) in ALL_SIGNALS.iter().enumerate() {
         if signal == signal_name_or_value || (format!("SIG{}", signal)) == signal_name_or_value {
             println!("{}", value);
-            exit!(EXIT_OK as i32)
+            return Ok(());
         } else if signal_name_or_value == value.to_string() {
             println!("{}", signal);
-            exit!(EXIT_OK as i32)
+            return Ok(());
         }
     }
-    crash!(EXIT_ERR, "unknown signal name {}", signal_name_or_value)
+    Err(USimpleError::new(
+        1,
+        format!("unknown signal name {}", signal_name_or_value),
+    ))
 }
 
 fn print_signals() {
@@ -170,30 +173,41 @@ fn print_signals() {
     }
 }
 
-fn list(arg: Option<String>) {
+fn list(arg: Option<String>) -> UResult<()> {
     match arg {
         Some(ref x) => print_signal(x),
-        None => print_signals(),
-    };
+        None => {
+            print_signals();
+            Ok(())
+        }
+    }
 }
 
-fn kill(signalname: &str, pids: &[String]) -> i32 {
-    let mut status = 0;
+fn kill(signalname: &str, pids: &[String]) -> UResult<()> {
     let optional_signal_value = uucore::signals::signal_by_name_or_value(signalname);
     let signal_value = match optional_signal_value {
         Some(x) => x,
-        None => crash!(EXIT_ERR, "unknown signal name {}", signalname),
+        None => {
+            return Err(USimpleError::new(
+                1,
+                format!("unknown signal name {}", signalname),
+            ));
+        }
     };
     for pid in pids {
         match pid.parse::<usize>() {
             Ok(x) => {
                 if unsafe { libc::kill(x as pid_t, signal_value as c_int) } != 0 {
-                    show_error!("{}", Error::last_os_error());
-                    status = 1;
+                    show!(USimpleError::new(1, format!("{}", Error::last_os_error())));
                 }
             }
-            Err(e) => crash!(EXIT_ERR, "failed to parse argument {}: {}", pid, e),
+            Err(e) => {
+                return Err(USimpleError::new(
+                    1,
+                    format!("failed to parse argument {}: {}", pid, e),
+                ));
+            }
         };
     }
-    status
+    Ok(())
 }
diff --git a/src/uu/ln/src/ln.rs b/src/uu/ln/src/ln.rs
index b08eba97a..65bdcf36c 100644
--- a/src/uu/ln/src/ln.rs
+++ b/src/uu/ln/src/ln.rs
@@ -11,9 +11,12 @@
 extern crate uucore;
 
 use clap::{crate_version, App, Arg};
+use uucore::error::{UCustomError, UResult};
 
 use std::borrow::Cow;
+use std::error::Error;
 use std::ffi::OsStr;
+use std::fmt::Display;
 use std::fs;
 
 use std::io::{stdin, Result};
@@ -22,6 +25,7 @@ use std::os::unix::fs::symlink;
 #[cfg(windows)]
 use std::os::windows::fs::{symlink_dir, symlink_file};
 use std::path::{Path, PathBuf};
+use uucore::backup_control::{self, BackupMode};
 use uucore::fs::{canonicalize, CanonicalizeMode};
 
 pub struct Settings {
@@ -43,12 +47,49 @@ pub enum OverwriteMode {
     Force,
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
-pub enum BackupMode {
-    NoBackup,
-    SimpleBackup,
-    NumberedBackup,
-    ExistingBackup,
+#[derive(Debug)]
+enum LnError {
+    TargetIsDirectory(String),
+    SomeLinksFailed,
+    FailedToLink(String),
+    MissingDestination(String),
+    ExtraOperand(String),
+    InvalidBackupMode(String),
+}
+
+impl Display for LnError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::TargetIsDirectory(s) => write!(f, "target '{}' is not a directory", s),
+            Self::FailedToLink(s) => write!(f, "failed to link '{}'", s),
+            Self::SomeLinksFailed => write!(f, "some links failed to create"),
+            Self::MissingDestination(s) => {
+                write!(f, "missing destination file operand after '{}'", s)
+            }
+            Self::ExtraOperand(s) => write!(
+                f,
+                "extra operand '{}'\nTry '{} --help' for more information.",
+                s,
+                executable!()
+            ),
+            Self::InvalidBackupMode(s) => write!(f, "{}", s),
+        }
+    }
+}
+
+impl Error for LnError {}
+
+impl UCustomError for LnError {
+    fn code(&self) -> i32 {
+        match self {
+            Self::TargetIsDirectory(_) => 1,
+            Self::SomeLinksFailed => 1,
+            Self::FailedToLink(_) => 1,
+            Self::MissingDestination(_) => 1,
+            Self::ExtraOperand(_) => 1,
+            Self::InvalidBackupMode(_) => 1,
+        }
+    }
 }
 
 fn get_usage() -> String {
@@ -78,7 +119,7 @@ fn get_long_usage() -> String {
 static ABOUT: &str = "change file owner and group";
 
 mod options {
-    pub const B: &str = "b";
+    pub const BACKUP_NO_ARG: &str = "b";
     pub const BACKUP: &str = "backup";
     pub const FORCE: &str = "force";
     pub const INTERACTIVE: &str = "interactive";
@@ -93,13 +134,18 @@ mod options {
 
 static ARG_FILES: &str = "files";
 
-pub fn uumain(args: impl uucore::Args) -> i32 {
+#[uucore_procs::gen_uumain]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let usage = get_usage();
     let long_usage = get_long_usage();
 
     let matches = uu_app()
         .usage(&usage[..])
-        .after_help(&long_usage[..])
+        .after_help(&*format!(
+            "{}\n{}",
+            long_usage,
+            backup_control::BACKUP_CONTROL_LONG_HELP
+        ))
         .get_matches_from(args);
 
     /* the list of files */
@@ -118,33 +164,24 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
         OverwriteMode::NoClobber
     };
 
-    let backup_mode = if matches.is_present(options::B) {
-        BackupMode::ExistingBackup
-    } else if matches.is_present(options::BACKUP) {
-        match matches.value_of(options::BACKUP) {
-            None => BackupMode::ExistingBackup,
-            Some(mode) => match mode {
-                "simple" | "never" => BackupMode::SimpleBackup,
-                "numbered" | "t" => BackupMode::NumberedBackup,
-                "existing" | "nil" => BackupMode::ExistingBackup,
-                "none" | "off" => BackupMode::NoBackup,
-                _ => panic!(), // cannot happen as it is managed by clap
-            },
+    let backup_mode = backup_control::determine_backup_mode(
+        matches.is_present(options::BACKUP_NO_ARG),
+        matches.is_present(options::BACKUP),
+        matches.value_of(options::BACKUP),
+    );
+    let backup_mode = match backup_mode {
+        Err(err) => {
+            return Err(LnError::InvalidBackupMode(err).into());
         }
-    } else {
-        BackupMode::NoBackup
+        Ok(mode) => mode,
     };
 
-    let backup_suffix = if matches.is_present(options::SUFFIX) {
-        matches.value_of(options::SUFFIX).unwrap()
-    } else {
-        "~"
-    };
+    let backup_suffix = backup_control::determine_backup_suffix(matches.value_of(options::SUFFIX));
 
     let settings = Settings {
         overwrite: overwrite_mode,
         backup: backup_mode,
-        suffix: backup_suffix.to_string(),
+        suffix: backup_suffix,
         symbolic: matches.is_present(options::SYMBOLIC),
         relative: matches.is_present(options::RELATIVE),
         target_dir: matches
@@ -162,22 +199,19 @@ pub fn uu_app() -> App<'static, 'static> {
     App::new(executable!())
         .version(crate_version!())
         .about(ABOUT)
-        .arg(Arg::with_name(options::B).short(options::B).help(
-            "make a backup of each file that would otherwise be overwritten or \
-             removed",
-        ))
         .arg(
             Arg::with_name(options::BACKUP)
                 .long(options::BACKUP)
-                .help(
-                    "make a backup of each file that would otherwise be overwritten \
-                     or removed",
-                )
+                .help("make a backup of each existing destination file")
                 .takes_value(true)
-                .possible_values(&[
-                    "simple", "never", "numbered", "t", "existing", "nil", "none", "off",
-                ])
-                .value_name("METHOD"),
+                .require_equals(true)
+                .min_values(0)
+                .value_name("CONTROL"),
+        )
+        .arg(
+            Arg::with_name(options::BACKUP_NO_ARG)
+                .short(options::BACKUP_NO_ARG)
+                .help("like --backup but does not accept an argument"),
         )
         // TODO: opts.arg(
         //    Arg::with_name(("d", "directory", "allow users with appropriate privileges to attempt \
@@ -260,7 +294,7 @@ pub fn uu_app() -> App<'static, 'static> {
         )
 }
 
-fn exec(files: &[PathBuf], settings: &Settings) -> i32 {
+fn exec(files: &[PathBuf], settings: &Settings) -> UResult<()> {
     // Handle cases where we create links in a directory first.
     if let Some(ref name) = settings.target_dir {
         // 4th form: a directory is specified by -t.
@@ -281,35 +315,22 @@ fn exec(files: &[PathBuf], settings: &Settings) -> i32 {
     // 1st form. Now there should be only two operands, but if -T is
     // specified we may have a wrong number of operands.
     if files.len() == 1 {
-        show_error!(
-            "missing destination file operand after '{}'",
-            files[0].to_string_lossy()
-        );
-        return 1;
+        return Err(LnError::MissingDestination(files[0].to_string_lossy().into()).into());
     }
     if files.len() > 2 {
-        show_error!(
-            "extra operand '{}'\nTry '{} --help' for more information.",
-            files[2].display(),
-            executable!()
-        );
-        return 1;
+        return Err(LnError::ExtraOperand(files[2].display().to_string()).into());
     }
     assert!(!files.is_empty());
 
     match link(&files[0], &files[1], settings) {
-        Ok(_) => 0,
-        Err(e) => {
-            show_error!("{}", e);
-            1
-        }
+        Ok(_) => Ok(()),
+        Err(e) => Err(LnError::FailedToLink(e.to_string()).into()),
     }
 }
 
-fn link_files_in_dir(files: &[PathBuf], target_dir: &Path, settings: &Settings) -> i32 {
+fn link_files_in_dir(files: &[PathBuf], target_dir: &Path, settings: &Settings) -> UResult<()> {
     if !target_dir.is_dir() {
-        show_error!("target '{}' is not a directory", target_dir.display());
-        return 1;
+        return Err(LnError::TargetIsDirectory(target_dir.display().to_string()).into());
     }
 
     let mut all_successful = true;
@@ -368,9 +389,9 @@ fn link_files_in_dir(files: &[PathBuf], target_dir: &Path, settings: &Settings)
         }
     }
     if all_successful {
-        0
+        Ok(())
     } else {
-        1
+        Err(LnError::SomeLinksFailed.into())
     }
 }
 
diff --git a/src/uu/ls/src/ls.rs b/src/uu/ls/src/ls.rs
index a2c6f3481..8fcd34bed 100644
--- a/src/uu/ls/src/ls.rs
+++ b/src/uu/ls/src/ls.rs
@@ -7,9 +7,6 @@
 
 // spell-checker:ignore (ToDO) cpio svgz webm somegroup nlink rmvb xspf
 
-// clippy bug https://github.com/rust-lang/rust-clippy/issues/7422
-#![allow(clippy::nonstandard_macro_braces)]
-
 #[macro_use]
 extern crate uucore;
 #[cfg(unix)]
diff --git a/src/uu/mkdir/src/mkdir.rs b/src/uu/mkdir/src/mkdir.rs
index 7362601ba..a99867570 100644
--- a/src/uu/mkdir/src/mkdir.rs
+++ b/src/uu/mkdir/src/mkdir.rs
@@ -5,9 +5,6 @@
 //  * For the full copyright and license information, please view the LICENSE
 //  * file that was distributed with this source code.
 
-// clippy bug https://github.com/rust-lang/rust-clippy/issues/7422
-#![allow(clippy::nonstandard_macro_braces)]
-
 #[macro_use]
 extern crate uucore;
 
diff --git a/src/uu/mktemp/src/mktemp.rs b/src/uu/mktemp/src/mktemp.rs
index ef5c41abf..8a4b472aa 100644
--- a/src/uu/mktemp/src/mktemp.rs
+++ b/src/uu/mktemp/src/mktemp.rs
@@ -8,9 +8,6 @@
 
 // spell-checker:ignore (paths) GPGHome
 
-// clippy bug https://github.com/rust-lang/rust-clippy/issues/7422
-#![allow(clippy::nonstandard_macro_braces)]
-
 #[macro_use]
 extern crate uucore;
 
diff --git a/src/uu/mv/src/mv.rs b/src/uu/mv/src/mv.rs
index 4a761861f..166e8cb1a 100644
--- a/src/uu/mv/src/mv.rs
+++ b/src/uu/mv/src/mv.rs
@@ -86,9 +86,17 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
 
     let overwrite_mode = determine_overwrite_mode(&matches);
     let backup_mode = backup_control::determine_backup_mode(
-        matches.is_present(OPT_BACKUP_NO_ARG) || matches.is_present(OPT_BACKUP),
+        matches.is_present(OPT_BACKUP_NO_ARG),
+        matches.is_present(OPT_BACKUP),
         matches.value_of(OPT_BACKUP),
     );
+    let backup_mode = match backup_mode {
+        Err(err) => {
+            show_usage_error!("{}", err);
+            return 1;
+        }
+        Ok(mode) => mode,
+    };
 
     if overwrite_mode == OverwriteMode::NoClobber && backup_mode != BackupMode::NoBackup {
         show_usage_error!("options --backup and --no-clobber are mutually exclusive");
@@ -135,7 +143,6 @@ pub fn uu_app() -> App<'static, 'static> {
             .takes_value(true)
             .require_equals(true)
             .min_values(0)
-            .possible_values(backup_control::BACKUP_CONTROL_VALUES)
             .value_name("CONTROL")
     )
     .arg(
diff --git a/src/uu/pathchk/src/pathchk.rs b/src/uu/pathchk/src/pathchk.rs
index 335266456..7f728667f 100644
--- a/src/uu/pathchk/src/pathchk.rs
+++ b/src/uu/pathchk/src/pathchk.rs
@@ -170,7 +170,7 @@ fn check_basic(path: &[String]) -> bool {
 fn check_extra(path: &[String]) -> bool {
     // components: leading hyphens
     for p in path {
-        if !no_leading_hyphen(p) {
+        if p.starts_with('-') {
             writeln!(
                 &mut std::io::stderr(),
                 "leading hyphen in file name component '{}'",
@@ -236,11 +236,6 @@ fn check_searchable(path: &str) -> bool {
     }
 }
 
-// check for a hyphen at the beginning of a path segment
-fn no_leading_hyphen(path_segment: &str) -> bool {
-    !path_segment.starts_with('-')
-}
-
 // check whether a path segment contains only valid (read: portable) characters
 fn check_portable_chars(path_segment: &str) -> bool {
     const VALID_CHARS: &[u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789._-";
diff --git a/src/uu/pwd/src/pwd.rs b/src/uu/pwd/src/pwd.rs
index 764a63a88..37effe618 100644
--- a/src/uu/pwd/src/pwd.rs
+++ b/src/uu/pwd/src/pwd.rs
@@ -13,6 +13,8 @@ use std::env;
 use std::io;
 use std::path::{Path, PathBuf};
 
+use uucore::error::{FromIo, UResult, USimpleError};
+
 static ABOUT: &str = "Display the full filename of the current working directory.";
 static OPT_LOGICAL: &str = "logical";
 static OPT_PHYSICAL: &str = "physical";
@@ -36,7 +38,8 @@ fn get_usage() -> String {
     format!("{0} [OPTION]... FILE...", executable!())
 }
 
-pub fn uumain(args: impl uucore::Args) -> i32 {
+#[uucore_procs::gen_uumain]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let usage = get_usage();
 
     let matches = uu_app().usage(&usage[..]).get_matches_from(args);
@@ -46,16 +49,20 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
             if matches.is_present(OPT_LOGICAL) {
                 println!("{}", logical_path.display());
             } else {
-                match absolute_path(&logical_path) {
-                    Ok(physical_path) => println!("{}", physical_path.display()),
-                    Err(e) => crash!(1, "failed to get absolute path {}", e),
-                };
+                let physical_path = absolute_path(&logical_path)
+                    .map_err_context(|| "failed to get absolute path".to_string())?;
+                println!("{}", physical_path.display());
             }
         }
-        Err(e) => crash!(1, "failed to get current directory {}", e),
+        Err(e) => {
+            return Err(USimpleError::new(
+                1,
+                format!("failed to get current directory {}", e),
+            ))
+        }
     };
 
-    0
+    Ok(())
 }
 
 pub fn uu_app() -> App<'static, 'static> {
diff --git a/src/uu/sleep/src/sleep.rs b/src/uu/sleep/src/sleep.rs
index ada3336df..127804a9f 100644
--- a/src/uu/sleep/src/sleep.rs
+++ b/src/uu/sleep/src/sleep.rs
@@ -11,6 +11,8 @@ extern crate uucore;
 use std::thread;
 use std::time::Duration;
 
+use uucore::error::{UResult, USimpleError};
+
 use clap::{crate_version, App, Arg};
 
 static ABOUT: &str = "Pause for NUMBER seconds.";
@@ -32,17 +34,18 @@ fn get_usage() -> String {
     )
 }
 
-pub fn uumain(args: impl uucore::Args) -> i32 {
+#[uucore_procs::gen_uumain]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let usage = get_usage();
 
     let matches = uu_app().usage(&usage[..]).get_matches_from(args);
 
     if let Some(values) = matches.values_of(options::NUMBER) {
         let numbers = values.collect();
-        sleep(numbers);
+        return sleep(numbers);
     }
 
-    0
+    Ok(())
 }
 
 pub fn uu_app() -> App<'static, 'static> {
@@ -61,15 +64,15 @@ pub fn uu_app() -> App<'static, 'static> {
         )
 }
 
-fn sleep(args: Vec<&str>) {
+fn sleep(args: Vec<&str>) -> UResult<()> {
     let sleep_dur =
-        args.iter().fold(
+        args.iter().try_fold(
             Duration::new(0, 0),
             |result, arg| match uucore::parse_time::from_str(&arg[..]) {
-                Ok(m) => m + result,
-                Err(f) => crash!(1, "{}", f),
+                Ok(m) => Ok(m + result),
+                Err(f) => Err(USimpleError::new(1, f)),
             },
-        );
-
+        )?;
     thread::sleep(sleep_dur);
+    Ok(())
 }
diff --git a/src/uu/sort/src/check.rs b/src/uu/sort/src/check.rs
index f1cd22686..5be752be0 100644
--- a/src/uu/sort/src/check.rs
+++ b/src/uu/sort/src/check.rs
@@ -9,24 +9,33 @@
 
 use crate::{
     chunks::{self, Chunk, RecycledChunk},
-    compare_by, open, GlobalSettings,
+    compare_by, open, GlobalSettings, SortError,
 };
 use itertools::Itertools;
 use std::{
     cmp::Ordering,
+    ffi::OsStr,
     io::Read,
     iter,
     sync::mpsc::{sync_channel, Receiver, SyncSender},
     thread,
 };
+use uucore::error::UResult;
 
 /// Check if the file at `path` is ordered.
 ///
 /// # Returns
 ///
 /// The code we should exit with.
-pub fn check(path: &str, settings: &GlobalSettings) -> i32 {
-    let file = open(path);
+pub fn check(path: &OsStr, settings: &GlobalSettings) -> UResult<()> {
+    let max_allowed_cmp = if settings.unique {
+        // If `unique` is enabled, the previous line must compare _less_ to the next one.
+        Ordering::Less
+    } else {
+        // Otherwise, the line previous line must compare _less or equal_ to the next one.
+        Ordering::Equal
+    };
+    let file = open(path)?;
     let (recycled_sender, recycled_receiver) = sync_channel(2);
     let (loaded_sender, loaded_receiver) = sync_channel(2);
     thread::spawn({
@@ -34,7 +43,13 @@ pub fn check(path: &str, settings: &GlobalSettings) -> i32 {
         move || reader(file, recycled_receiver, loaded_sender, &settings)
     });
     for _ in 0..2 {
-        let _ = recycled_sender.send(RecycledChunk::new(100 * 1024));
+        let _ = recycled_sender.send(RecycledChunk::new(if settings.buffer_size < 100 * 1024 {
+            // when the buffer size is smaller than 100KiB we choose it instead of the default.
+            // this improves testability.
+            settings.buffer_size
+        } else {
+            100 * 1024
+        }));
     }
 
     let mut prev_chunk: Option<Chunk> = None;
@@ -53,30 +68,35 @@ pub fn check(path: &str, settings: &GlobalSettings) -> i32 {
                 settings,
                 prev_chunk.line_data(),
                 chunk.line_data(),
-            ) == Ordering::Greater
+            ) > max_allowed_cmp
             {
-                if !settings.check_silent {
-                    println!("sort: {}:{}: disorder: {}", path, line_idx, new_first.line);
+                return Err(SortError::Disorder {
+                    file: path.to_owned(),
+                    line_number: line_idx,
+                    line: new_first.line.to_owned(),
+                    silent: settings.check_silent,
                 }
-                return 1;
+                .into());
             }
             let _ = recycled_sender.send(prev_chunk.recycle());
         }
 
         for (a, b) in chunk.lines().iter().tuple_windows() {
             line_idx += 1;
-            if compare_by(a, b, settings, chunk.line_data(), chunk.line_data()) == Ordering::Greater
-            {
-                if !settings.check_silent {
-                    println!("sort: {}:{}: disorder: {}", path, line_idx, b.line);
+            if compare_by(a, b, settings, chunk.line_data(), chunk.line_data()) > max_allowed_cmp {
+                return Err(SortError::Disorder {
+                    file: path.to_owned(),
+                    line_number: line_idx,
+                    line: b.line.to_owned(),
+                    silent: settings.check_silent,
                 }
-                return 1;
+                .into());
             }
         }
 
         prev_chunk = Some(chunk);
     }
-    0
+    Ok(())
 }
 
 /// The function running on the reader thread.
@@ -85,7 +105,7 @@ fn reader(
     receiver: Receiver<RecycledChunk>,
     sender: SyncSender<Chunk>,
     settings: &GlobalSettings,
-) {
+) -> UResult<()> {
     let mut carry_over = vec![];
     for recycled_chunk in receiver.iter() {
         let should_continue = chunks::read(
@@ -101,9 +121,10 @@ fn reader(
                 b'\n'
             },
             settings,
-        );
+        )?;
         if !should_continue {
             break;
         }
     }
+    Ok(())
 }
diff --git a/src/uu/sort/src/chunks.rs b/src/uu/sort/src/chunks.rs
index 9e9d212c2..80d6060d4 100644
--- a/src/uu/sort/src/chunks.rs
+++ b/src/uu/sort/src/chunks.rs
@@ -14,8 +14,9 @@ use std::{
 
 use memchr::memchr_iter;
 use ouroboros::self_referencing;
+use uucore::error::{UResult, USimpleError};
 
-use crate::{numeric_str_cmp::NumInfo, GeneralF64ParseResult, GlobalSettings, Line};
+use crate::{numeric_str_cmp::NumInfo, GeneralF64ParseResult, GlobalSettings, Line, SortError};
 
 /// The chunk that is passed around between threads.
 /// `lines` consist of slices into `buffer`.
@@ -137,10 +138,10 @@ pub fn read<T: Read>(
     max_buffer_size: Option<usize>,
     carry_over: &mut Vec<u8>,
     file: &mut T,
-    next_files: &mut impl Iterator<Item = T>,
+    next_files: &mut impl Iterator<Item = UResult<T>>,
     separator: u8,
     settings: &GlobalSettings,
-) -> bool {
+) -> UResult<bool> {
     let RecycledChunk {
         lines,
         selections,
@@ -159,12 +160,12 @@ pub fn read<T: Read>(
         max_buffer_size,
         carry_over.len(),
         separator,
-    );
+    )?;
     carry_over.clear();
     carry_over.extend_from_slice(&buffer[read..]);
 
     if read != 0 {
-        let payload = Chunk::new(buffer, |buffer| {
+        let payload: UResult<Chunk> = Chunk::try_new(buffer, |buffer| {
             let selections = unsafe {
                 // SAFETY: It is safe to transmute to an empty vector of selections with shorter lifetime.
                 // It was only temporarily transmuted to a Vec<Line<'static>> to make recycling possible.
@@ -175,18 +176,19 @@ pub fn read<T: Read>(
                 // because it was only temporarily transmuted to a Vec<Line<'static>> to make recycling possible.
                 std::mem::transmute::<Vec<Line<'static>>, Vec<Line<'_>>>(lines)
             };
-            let read = crash_if_err!(1, std::str::from_utf8(&buffer[..read]));
+            let read = std::str::from_utf8(&buffer[..read])
+                .map_err(|error| SortError::Uft8Error { error })?;
             let mut line_data = LineData {
                 selections,
                 num_infos,
                 parsed_floats,
             };
             parse_lines(read, &mut lines, &mut line_data, separator, settings);
-            ChunkContents { lines, line_data }
+            Ok(ChunkContents { lines, line_data })
         });
-        sender.send(payload).unwrap();
+        sender.send(payload?).unwrap();
     }
-    should_continue
+    Ok(should_continue)
 }
 
 /// Split `read` into `Line`s, and add them to `lines`.
@@ -242,12 +244,12 @@ fn parse_lines<'a>(
 /// * Whether this function should be called again.
 fn read_to_buffer<T: Read>(
     file: &mut T,
-    next_files: &mut impl Iterator<Item = T>,
+    next_files: &mut impl Iterator<Item = UResult<T>>,
     buffer: &mut Vec<u8>,
     max_buffer_size: Option<usize>,
     start_offset: usize,
     separator: u8,
-) -> (usize, bool) {
+) -> UResult<(usize, bool)> {
     let mut read_target = &mut buffer[start_offset..];
     let mut last_file_target_size = read_target.len();
     loop {
@@ -274,7 +276,7 @@ fn read_to_buffer<T: Read>(
                         // We read enough lines.
                         let end = last_line_end.unwrap();
                         // We want to include the separator here, because it shouldn't be carried over.
-                        return (end + 1, true);
+                        return Ok((end + 1, true));
                     } else {
                         // We need to read more lines
                         let len = buffer.len();
@@ -299,11 +301,11 @@ fn read_to_buffer<T: Read>(
                     if let Some(next_file) = next_files.next() {
                         // There is another file.
                         last_file_target_size = leftover_len;
-                        *file = next_file;
+                        *file = next_file?;
                     } else {
                         // This was the last file.
                         let read_len = buffer.len() - leftover_len;
-                        return (read_len, false);
+                        return Ok((read_len, false));
                     }
                 }
             }
@@ -313,7 +315,7 @@ fn read_to_buffer<T: Read>(
             Err(e) if e.kind() == ErrorKind::Interrupted => {
                 // retry
             }
-            Err(e) => crash!(1, "{}", e),
+            Err(e) => return Err(USimpleError::new(2, e.to_string())),
         }
     }
 }
diff --git a/src/uu/sort/src/ext_sort.rs b/src/uu/sort/src/ext_sort.rs
index e0814b7a2..8ff5665fd 100644
--- a/src/uu/sort/src/ext_sort.rs
+++ b/src/uu/sort/src/ext_sort.rs
@@ -22,12 +22,15 @@ use std::{
 };
 
 use itertools::Itertools;
+use uucore::error::UResult;
 
 use crate::chunks::RecycledChunk;
 use crate::merge::ClosedTmpFile;
 use crate::merge::WriteableCompressedTmpFile;
 use crate::merge::WriteablePlainTmpFile;
 use crate::merge::WriteableTmpFile;
+use crate::Output;
+use crate::SortError;
 use crate::{
     chunks::{self, Chunk},
     compare_by, merge, sort_by, GlobalSettings,
@@ -38,7 +41,11 @@ use tempfile::TempDir;
 const START_BUFFER_SIZE: usize = 8_000;
 
 /// Sort files by using auxiliary files for storing intermediate chunks (if needed), and output the result.
-pub fn ext_sort(files: &mut impl Iterator<Item = Box<dyn Read + Send>>, settings: &GlobalSettings) {
+pub fn ext_sort(
+    files: &mut impl Iterator<Item = UResult<Box<dyn Read + Send>>>,
+    settings: &GlobalSettings,
+    output: Output,
+) -> UResult<()> {
     let (sorted_sender, sorted_receiver) = std::sync::mpsc::sync_channel(1);
     let (recycled_sender, recycled_receiver) = std::sync::mpsc::sync_channel(1);
     thread::spawn({
@@ -51,23 +58,29 @@ pub fn ext_sort(files: &mut impl Iterator<Item = Box<dyn Read + Send>>, settings
             settings,
             sorted_receiver,
             recycled_sender,
-        );
+            output,
+        )
     } else {
         reader_writer::<_, WriteablePlainTmpFile>(
             files,
             settings,
             sorted_receiver,
             recycled_sender,
-        );
+            output,
+        )
     }
 }
 
-fn reader_writer<F: Iterator<Item = Box<dyn Read + Send>>, Tmp: WriteableTmpFile + 'static>(
+fn reader_writer<
+    F: Iterator<Item = UResult<Box<dyn Read + Send>>>,
+    Tmp: WriteableTmpFile + 'static,
+>(
     files: F,
     settings: &GlobalSettings,
     receiver: Receiver<Chunk>,
     sender: SyncSender<Chunk>,
-) {
+    output: Output,
+) -> UResult<()> {
     let separator = if settings.zero_terminated {
         b'\0'
     } else {
@@ -81,22 +94,20 @@ fn reader_writer<F: Iterator<Item = Box<dyn Read + Send>>, Tmp: WriteableTmpFile
         files,
         &settings.tmp_dir,
         separator,
-        // Heuristically chosen: Dividing by 10 seems to keep our memory usage roughly
-        // around settings.buffer_size as a whole.
         buffer_size,
         settings,
         receiver,
         sender,
-    );
+    )?;
     match read_result {
         ReadResult::WroteChunksToFile { tmp_files, tmp_dir } => {
             let tmp_dir_size = tmp_files.len();
-            let mut merger = merge::merge_with_file_limit::<_, _, Tmp>(
+            let merger = merge::merge_with_file_limit::<_, _, Tmp>(
                 tmp_files.into_iter().map(|c| c.reopen()),
                 settings,
                 Some((tmp_dir, tmp_dir_size)),
-            );
-            merger.write_all(settings);
+            )?;
+            merger.write_all(settings, output)?;
         }
         ReadResult::SortedSingleChunk(chunk) => {
             if settings.unique {
@@ -106,9 +117,10 @@ fn reader_writer<F: Iterator<Item = Box<dyn Read + Send>>, Tmp: WriteableTmpFile
                             == Ordering::Equal
                     }),
                     settings,
+                    output,
                 );
             } else {
-                print_sorted(chunk.lines().iter(), settings);
+                print_sorted(chunk.lines().iter(), settings, output);
             }
         }
         ReadResult::SortedTwoChunks([a, b]) => {
@@ -128,15 +140,17 @@ fn reader_writer<F: Iterator<Item = Box<dyn Read + Send>>, Tmp: WriteableTmpFile
                         })
                         .map(|(line, _)| line),
                     settings,
+                    output,
                 );
             } else {
-                print_sorted(merged_iter.map(|(line, _)| line), settings);
+                print_sorted(merged_iter.map(|(line, _)| line), settings, output);
             }
         }
         ReadResult::EmptyInput => {
             // don't output anything
         }
     }
+    Ok(())
 }
 
 /// The function that is executed on the sorter thread.
@@ -145,7 +159,11 @@ fn sorter(receiver: Receiver<Chunk>, sender: SyncSender<Chunk>, settings: Global
         payload.with_contents_mut(|contents| {
             sort_by(&mut contents.lines, &settings, &contents.line_data)
         });
-        sender.send(payload).unwrap();
+        if sender.send(payload).is_err() {
+            // The receiver has gone away, likely because the other thread hit an error.
+            // We stop silently because the actual error is printed by the other thread.
+            return;
+        }
     }
 }
 
@@ -165,15 +183,15 @@ enum ReadResult<I: WriteableTmpFile> {
 }
 /// The function that is executed on the reader/writer thread.
 fn read_write_loop<I: WriteableTmpFile>(
-    mut files: impl Iterator<Item = Box<dyn Read + Send>>,
+    mut files: impl Iterator<Item = UResult<Box<dyn Read + Send>>>,
     tmp_dir_parent: &Path,
     separator: u8,
     buffer_size: usize,
     settings: &GlobalSettings,
     receiver: Receiver<Chunk>,
     sender: SyncSender<Chunk>,
-) -> ReadResult<I> {
-    let mut file = files.next().unwrap();
+) -> UResult<ReadResult<I>> {
+    let mut file = files.next().unwrap()?;
 
     let mut carry_over = vec![];
     // kick things off with two reads
@@ -191,14 +209,14 @@ fn read_write_loop<I: WriteableTmpFile>(
             &mut files,
             separator,
             settings,
-        );
+        )?;
 
         if !should_continue {
             drop(sender);
             // We have already read the whole input. Since we are in our first two reads,
             // this means that we can fit the whole input into memory. Bypass writing below and
             // handle this case in a more straightforward way.
-            return if let Ok(first_chunk) = receiver.recv() {
+            return Ok(if let Ok(first_chunk) = receiver.recv() {
                 if let Ok(second_chunk) = receiver.recv() {
                     ReadResult::SortedTwoChunks([first_chunk, second_chunk])
                 } else {
@@ -206,16 +224,14 @@ fn read_write_loop<I: WriteableTmpFile>(
                 }
             } else {
                 ReadResult::EmptyInput
-            };
+            });
         }
     }
 
-    let tmp_dir = crash_if_err!(
-        1,
-        tempfile::Builder::new()
-            .prefix("uutils_sort")
-            .tempdir_in(tmp_dir_parent)
-    );
+    let tmp_dir = tempfile::Builder::new()
+        .prefix("uutils_sort")
+        .tempdir_in(tmp_dir_parent)
+        .map_err(|_| SortError::TmpDirCreationFailed)?;
 
     let mut sender_option = Some(sender);
     let mut file_number = 0;
@@ -224,7 +240,7 @@ fn read_write_loop<I: WriteableTmpFile>(
         let mut chunk = match receiver.recv() {
             Ok(it) => it,
             _ => {
-                return ReadResult::WroteChunksToFile { tmp_files, tmp_dir };
+                return Ok(ReadResult::WroteChunksToFile { tmp_files, tmp_dir });
             }
         };
 
@@ -233,7 +249,7 @@ fn read_write_loop<I: WriteableTmpFile>(
             tmp_dir.path().join(file_number.to_string()),
             settings.compress_prog.as_deref(),
             separator,
-        );
+        )?;
         tmp_files.push(tmp_file);
 
         file_number += 1;
@@ -250,7 +266,7 @@ fn read_write_loop<I: WriteableTmpFile>(
                 &mut files,
                 separator,
                 settings,
-            );
+            )?;
             if !should_continue {
                 sender_option = None;
             }
@@ -265,8 +281,8 @@ fn write<I: WriteableTmpFile>(
     file: PathBuf,
     compress_prog: Option<&str>,
     separator: u8,
-) -> I::Closed {
-    let mut tmp_file = I::create(file, compress_prog);
+) -> UResult<I::Closed> {
+    let mut tmp_file = I::create(file, compress_prog)?;
     write_lines(chunk.lines(), tmp_file.as_write(), separator);
     tmp_file.finished_writing()
 }
diff --git a/src/uu/sort/src/merge.rs b/src/uu/sort/src/merge.rs
index 12d7a9b9b..fad966f64 100644
--- a/src/uu/sort/src/merge.rs
+++ b/src/uu/sort/src/merge.rs
@@ -9,44 +9,85 @@
 
 use std::{
     cmp::Ordering,
+    ffi::OsString,
     fs::{self, File},
     io::{BufWriter, Read, Write},
     iter,
-    path::PathBuf,
+    path::{Path, PathBuf},
     process::{Child, ChildStdin, ChildStdout, Command, Stdio},
     rc::Rc,
     sync::mpsc::{channel, sync_channel, Receiver, Sender, SyncSender},
-    thread,
+    thread::{self, JoinHandle},
 };
 
 use compare::Compare;
 use itertools::Itertools;
 use tempfile::TempDir;
+use uucore::error::UResult;
 
 use crate::{
     chunks::{self, Chunk, RecycledChunk},
-    compare_by, GlobalSettings,
+    compare_by, open, GlobalSettings, Output, SortError,
 };
 
+/// If the output file occurs in the input files as well, copy the contents of the output file
+/// and replace its occurrences in the inputs with that copy.
+fn replace_output_file_in_input_files(
+    files: &mut [OsString],
+    settings: &GlobalSettings,
+    output: Option<&str>,
+) -> UResult<Option<(TempDir, usize)>> {
+    let mut copy: Option<(TempDir, PathBuf)> = None;
+    if let Some(Ok(output_path)) = output.map(|path| Path::new(path).canonicalize()) {
+        for file in files {
+            if let Ok(file_path) = Path::new(file).canonicalize() {
+                if file_path == output_path {
+                    if let Some((_dir, copy)) = &copy {
+                        *file = copy.clone().into_os_string();
+                    } else {
+                        let tmp_dir = tempfile::Builder::new()
+                            .prefix("uutils_sort")
+                            .tempdir_in(&settings.tmp_dir)
+                            .map_err(|_| SortError::TmpDirCreationFailed)?;
+                        let copy_path = tmp_dir.path().join("0");
+                        std::fs::copy(file_path, &copy_path)
+                            .map_err(|error| SortError::OpenTmpFileFailed { error })?;
+                        *file = copy_path.clone().into_os_string();
+                        copy = Some((tmp_dir, copy_path))
+                    }
+                }
+            }
+        }
+    }
+    // if we created a TempDir its size must be one.
+    Ok(copy.map(|(dir, _copy)| (dir, 1)))
+}
+
 /// Merge pre-sorted `Box<dyn Read>`s.
 ///
 /// If `settings.merge_batch_size` is greater than the length of `files`, intermediate files will be used.
 /// If `settings.compress_prog` is `Some`, intermediate files will be compressed with it.
-pub fn merge<Files: ExactSizeIterator<Item = Box<dyn Read + Send>>>(
-    files: Files,
-    settings: &GlobalSettings,
-) -> FileMerger {
+pub fn merge<'a>(
+    files: &mut [OsString],
+    settings: &'a GlobalSettings,
+    output: Option<&str>,
+) -> UResult<FileMerger<'a>> {
+    let tmp_dir = replace_output_file_in_input_files(files, settings, output)?;
     if settings.compress_prog.is_none() {
         merge_with_file_limit::<_, _, WriteablePlainTmpFile>(
-            files.map(|file| PlainMergeInput { inner: file }),
+            files
+                .iter()
+                .map(|file| open(file).map(|file| PlainMergeInput { inner: file })),
             settings,
-            None,
+            tmp_dir,
         )
     } else {
         merge_with_file_limit::<_, _, WriteableCompressedTmpFile>(
-            files.map(|file| PlainMergeInput { inner: file }),
+            files
+                .iter()
+                .map(|file| open(file).map(|file| PlainMergeInput { inner: file })),
             settings,
-            None,
+            tmp_dir,
         )
     }
 }
@@ -54,24 +95,25 @@ pub fn merge<Files: ExactSizeIterator<Item = Box<dyn Read + Send>>>(
 // Merge already sorted `MergeInput`s.
 pub fn merge_with_file_limit<
     M: MergeInput + 'static,
-    F: ExactSizeIterator<Item = M>,
+    F: ExactSizeIterator<Item = UResult<M>>,
     Tmp: WriteableTmpFile + 'static,
 >(
     files: F,
     settings: &GlobalSettings,
     tmp_dir: Option<(TempDir, usize)>,
-) -> FileMerger {
+) -> UResult<FileMerger> {
     if files.len() > settings.merge_batch_size {
         // If we did not get a tmp_dir, create one.
-        let (tmp_dir, mut tmp_dir_size) = tmp_dir.unwrap_or_else(|| {
-            (
+        let (tmp_dir, mut tmp_dir_size) = match tmp_dir {
+            Some(x) => x,
+            None => (
                 tempfile::Builder::new()
                     .prefix("uutils_sort")
                     .tempdir_in(&settings.tmp_dir)
-                    .unwrap(),
+                    .map_err(|_| SortError::TmpDirCreationFailed)?,
                 0,
-            )
-        });
+            ),
+        };
         let mut remaining_files = files.len();
         let batches = files.chunks(settings.merge_batch_size);
         let mut batches = batches.into_iter();
@@ -79,14 +121,14 @@ pub fn merge_with_file_limit<
         while remaining_files != 0 {
             // Work around the fact that `Chunks` is not an `ExactSizeIterator`.
             remaining_files = remaining_files.saturating_sub(settings.merge_batch_size);
-            let mut merger = merge_without_limit(batches.next().unwrap(), settings);
+            let merger = merge_without_limit(batches.next().unwrap(), settings)?;
             let mut tmp_file = Tmp::create(
                 tmp_dir.path().join(tmp_dir_size.to_string()),
                 settings.compress_prog.as_deref(),
-            );
+            )?;
             tmp_dir_size += 1;
-            merger.write_all_to(settings, tmp_file.as_write());
-            temporary_files.push(tmp_file.finished_writing());
+            merger.write_all_to(settings, tmp_file.as_write())?;
+            temporary_files.push(tmp_file.finished_writing()?);
         }
         assert!(batches.next().is_none());
         merge_with_file_limit::<_, _, Tmp>(
@@ -94,7 +136,7 @@ pub fn merge_with_file_limit<
                 .into_iter()
                 .map(Box::new(|c: Tmp::Closed| c.reopen())
                     as Box<
-                        dyn FnMut(Tmp::Closed) -> <Tmp::Closed as ClosedTmpFile>::Reopened,
+                        dyn FnMut(Tmp::Closed) -> UResult<<Tmp::Closed as ClosedTmpFile>::Reopened>,
                     >),
             settings,
             Some((tmp_dir, tmp_dir_size)),
@@ -108,10 +150,10 @@ pub fn merge_with_file_limit<
 ///
 /// It is the responsibility of the caller to ensure that `files` yields only
 /// as many files as we are allowed to open concurrently.
-fn merge_without_limit<M: MergeInput + 'static, F: Iterator<Item = M>>(
+fn merge_without_limit<M: MergeInput + 'static, F: Iterator<Item = UResult<M>>>(
     files: F,
     settings: &GlobalSettings,
-) -> FileMerger {
+) -> UResult<FileMerger> {
     let (request_sender, request_receiver) = channel();
     let mut reader_files = Vec::with_capacity(files.size_hint().0);
     let mut loaded_receivers = Vec::with_capacity(files.size_hint().0);
@@ -119,7 +161,7 @@ fn merge_without_limit<M: MergeInput + 'static, F: Iterator<Item = M>>(
         let (sender, receiver) = sync_channel(2);
         loaded_receivers.push(receiver);
         reader_files.push(Some(ReaderFile {
-            file,
+            file: file?,
             sender,
             carry_over: vec![],
         }));
@@ -136,7 +178,7 @@ fn merge_without_limit<M: MergeInput + 'static, F: Iterator<Item = M>>(
             .unwrap();
     }
 
-    thread::spawn({
+    let reader_join_handle = thread::spawn({
         let settings = settings.clone();
         move || {
             reader(
@@ -155,22 +197,25 @@ fn merge_without_limit<M: MergeInput + 'static, F: Iterator<Item = M>>(
     let mut mergeable_files = vec![];
 
     for (file_number, receiver) in loaded_receivers.into_iter().enumerate() {
-        mergeable_files.push(MergeableFile {
-            current_chunk: Rc::new(receiver.recv().unwrap()),
-            file_number,
-            line_idx: 0,
-            receiver,
-        })
+        if let Ok(chunk) = receiver.recv() {
+            mergeable_files.push(MergeableFile {
+                current_chunk: Rc::new(chunk),
+                file_number,
+                line_idx: 0,
+                receiver,
+            })
+        }
     }
 
-    FileMerger {
+    Ok(FileMerger {
         heap: binary_heap_plus::BinaryHeap::from_vec_cmp(
             mergeable_files,
             FileComparator { settings },
         ),
         request_sender,
         prev: None,
-    }
+        reader_join_handle,
+    })
 }
 /// The struct on the reader thread representing an input file
 struct ReaderFile<M: MergeInput> {
@@ -185,7 +230,7 @@ fn reader(
     files: &mut [Option<ReaderFile<impl MergeInput>>],
     settings: &GlobalSettings,
     separator: u8,
-) {
+) -> UResult<()> {
     for (file_idx, recycled_chunk) in recycled_receiver.iter() {
         if let Some(ReaderFile {
             file,
@@ -202,15 +247,16 @@ fn reader(
                 &mut iter::empty(),
                 separator,
                 settings,
-            );
+            )?;
             if !should_continue {
                 // Remove the file from the list by replacing it with `None`.
                 let ReaderFile { file, .. } = files[file_idx].take().unwrap();
                 // Depending on the kind of the `MergeInput`, this may delete the file:
-                file.finished_reading();
+                file.finished_reading()?;
             }
         }
     }
+    Ok(())
 }
 /// The struct on the main thread representing an input file
 pub struct MergeableFile {
@@ -234,17 +280,20 @@ pub struct FileMerger<'a> {
     heap: binary_heap_plus::BinaryHeap<MergeableFile, FileComparator<'a>>,
     request_sender: Sender<(usize, RecycledChunk)>,
     prev: Option<PreviousLine>,
+    reader_join_handle: JoinHandle<UResult<()>>,
 }
 
 impl<'a> FileMerger<'a> {
     /// Write the merged contents to the output file.
-    pub fn write_all(&mut self, settings: &GlobalSettings) {
-        let mut out = settings.out_writer();
-        self.write_all_to(settings, &mut out);
+    pub fn write_all(self, settings: &GlobalSettings, output: Output) -> UResult<()> {
+        let mut out = output.into_write();
+        self.write_all_to(settings, &mut out)
     }
 
-    pub fn write_all_to(&mut self, settings: &GlobalSettings, out: &mut impl Write) {
+    pub fn write_all_to(mut self, settings: &GlobalSettings, out: &mut impl Write) -> UResult<()> {
         while self.write_next(settings, out) {}
+        drop(self.request_sender);
+        self.reader_join_handle.join().unwrap()
     }
 
     fn write_next(&mut self, settings: &GlobalSettings, out: &mut impl Write) -> bool {
@@ -328,36 +377,41 @@ impl<'a> Compare<MergeableFile> for FileComparator<'a> {
 }
 
 // Wait for the child to exit and check its exit code.
-fn assert_child_success(mut child: Child, program: &str) {
+fn check_child_success(mut child: Child, program: &str) -> UResult<()> {
     if !matches!(
         child.wait().map(|e| e.code()),
         Ok(Some(0)) | Ok(None) | Err(_)
     ) {
-        crash!(2, "'{}' terminated abnormally", program)
+        Err(SortError::CompressProgTerminatedAbnormally {
+            prog: program.to_owned(),
+        }
+        .into())
+    } else {
+        Ok(())
     }
 }
 
 /// A temporary file that can be written to.
-pub trait WriteableTmpFile {
+pub trait WriteableTmpFile: Sized {
     type Closed: ClosedTmpFile;
     type InnerWrite: Write;
-    fn create(path: PathBuf, compress_prog: Option<&str>) -> Self;
+    fn create(path: PathBuf, compress_prog: Option<&str>) -> UResult<Self>;
     /// Closes the temporary file.
-    fn finished_writing(self) -> Self::Closed;
+    fn finished_writing(self) -> UResult<Self::Closed>;
     fn as_write(&mut self) -> &mut Self::InnerWrite;
 }
 /// A temporary file that is (temporarily) closed, but can be reopened.
 pub trait ClosedTmpFile {
     type Reopened: MergeInput;
     /// Reopens the temporary file.
-    fn reopen(self) -> Self::Reopened;
+    fn reopen(self) -> UResult<Self::Reopened>;
 }
 /// A pre-sorted input for merging.
 pub trait MergeInput: Send {
     type InnerRead: Read;
     /// Cleans this `MergeInput` up.
     /// Implementations may delete the backing file.
-    fn finished_reading(self);
+    fn finished_reading(self) -> UResult<()>;
     fn as_read(&mut self) -> &mut Self::InnerRead;
 }
 
@@ -376,15 +430,17 @@ impl WriteableTmpFile for WriteablePlainTmpFile {
     type Closed = ClosedPlainTmpFile;
     type InnerWrite = BufWriter<File>;
 
-    fn create(path: PathBuf, _: Option<&str>) -> Self {
-        WriteablePlainTmpFile {
-            file: BufWriter::new(File::create(&path).unwrap()),
+    fn create(path: PathBuf, _: Option<&str>) -> UResult<Self> {
+        Ok(WriteablePlainTmpFile {
+            file: BufWriter::new(
+                File::create(&path).map_err(|error| SortError::OpenTmpFileFailed { error })?,
+            ),
             path,
-        }
+        })
     }
 
-    fn finished_writing(self) -> Self::Closed {
-        ClosedPlainTmpFile { path: self.path }
+    fn finished_writing(self) -> UResult<Self::Closed> {
+        Ok(ClosedPlainTmpFile { path: self.path })
     }
 
     fn as_write(&mut self) -> &mut Self::InnerWrite {
@@ -393,18 +449,22 @@ impl WriteableTmpFile for WriteablePlainTmpFile {
 }
 impl ClosedTmpFile for ClosedPlainTmpFile {
     type Reopened = PlainTmpMergeInput;
-    fn reopen(self) -> Self::Reopened {
-        PlainTmpMergeInput {
-            file: File::open(&self.path).unwrap(),
+    fn reopen(self) -> UResult<Self::Reopened> {
+        Ok(PlainTmpMergeInput {
+            file: File::open(&self.path).map_err(|error| SortError::OpenTmpFileFailed { error })?,
             path: self.path,
-        }
+        })
     }
 }
 impl MergeInput for PlainTmpMergeInput {
     type InnerRead = File;
 
-    fn finished_reading(self) {
-        fs::remove_file(self.path).ok();
+    fn finished_reading(self) -> UResult<()> {
+        // we ignore failures to delete the temporary file,
+        // because there is a race at the end of the execution and the whole
+        // temporary directory might already be gone.
+        let _ = fs::remove_file(self.path);
+        Ok(())
     }
 
     fn as_read(&mut self) -> &mut Self::InnerRead {
@@ -432,35 +492,33 @@ impl WriteableTmpFile for WriteableCompressedTmpFile {
     type Closed = ClosedCompressedTmpFile;
     type InnerWrite = BufWriter<ChildStdin>;
 
-    fn create(path: PathBuf, compress_prog: Option<&str>) -> Self {
+    fn create(path: PathBuf, compress_prog: Option<&str>) -> UResult<Self> {
         let compress_prog = compress_prog.unwrap();
         let mut command = Command::new(compress_prog);
-        command
-            .stdin(Stdio::piped())
-            .stdout(File::create(&path).unwrap());
-        let mut child = crash_if_err!(
-            2,
-            command.spawn().map_err(|err| format!(
-                "couldn't execute compress program: errno {}",
-                err.raw_os_error().unwrap()
-            ))
-        );
+        let tmp_file =
+            File::create(&path).map_err(|error| SortError::OpenTmpFileFailed { error })?;
+        command.stdin(Stdio::piped()).stdout(tmp_file);
+        let mut child = command
+            .spawn()
+            .map_err(|err| SortError::CompressProgExecutionFailed {
+                code: err.raw_os_error().unwrap(),
+            })?;
         let child_stdin = child.stdin.take().unwrap();
-        WriteableCompressedTmpFile {
+        Ok(WriteableCompressedTmpFile {
             path,
             compress_prog: compress_prog.to_owned(),
             child,
             child_stdin: BufWriter::new(child_stdin),
-        }
+        })
     }
 
-    fn finished_writing(self) -> Self::Closed {
+    fn finished_writing(self) -> UResult<Self::Closed> {
         drop(self.child_stdin);
-        assert_child_success(self.child, &self.compress_prog);
-        ClosedCompressedTmpFile {
+        check_child_success(self.child, &self.compress_prog)?;
+        Ok(ClosedCompressedTmpFile {
             path: self.path,
             compress_prog: self.compress_prog,
-        }
+        })
     }
 
     fn as_write(&mut self) -> &mut Self::InnerWrite {
@@ -470,33 +528,32 @@ impl WriteableTmpFile for WriteableCompressedTmpFile {
 impl ClosedTmpFile for ClosedCompressedTmpFile {
     type Reopened = CompressedTmpMergeInput;
 
-    fn reopen(self) -> Self::Reopened {
+    fn reopen(self) -> UResult<Self::Reopened> {
         let mut command = Command::new(&self.compress_prog);
         let file = File::open(&self.path).unwrap();
         command.stdin(file).stdout(Stdio::piped()).arg("-d");
-        let mut child = crash_if_err!(
-            2,
-            command.spawn().map_err(|err| format!(
-                "couldn't execute compress program: errno {}",
-                err.raw_os_error().unwrap()
-            ))
-        );
+        let mut child = command
+            .spawn()
+            .map_err(|err| SortError::CompressProgExecutionFailed {
+                code: err.raw_os_error().unwrap(),
+            })?;
         let child_stdout = child.stdout.take().unwrap();
-        CompressedTmpMergeInput {
+        Ok(CompressedTmpMergeInput {
             path: self.path,
             compress_prog: self.compress_prog,
             child,
             child_stdout,
-        }
+        })
     }
 }
 impl MergeInput for CompressedTmpMergeInput {
     type InnerRead = ChildStdout;
 
-    fn finished_reading(self) {
+    fn finished_reading(self) -> UResult<()> {
         drop(self.child_stdout);
-        assert_child_success(self.child, &self.compress_prog);
-        fs::remove_file(self.path).ok();
+        check_child_success(self.child, &self.compress_prog)?;
+        let _ = fs::remove_file(self.path);
+        Ok(())
     }
 
     fn as_read(&mut self) -> &mut Self::InnerRead {
@@ -509,7 +566,9 @@ pub struct PlainMergeInput<R: Read + Send> {
 }
 impl<R: Read + Send> MergeInput for PlainMergeInput<R> {
     type InnerRead = R;
-    fn finished_reading(self) {}
+    fn finished_reading(self) -> UResult<()> {
+        Ok(())
+    }
     fn as_read(&mut self) -> &mut Self::InnerRead {
         &mut self.inner
     }
diff --git a/src/uu/sort/src/sort.rs b/src/uu/sort/src/sort.rs
index 55bcdb77b..be9510aef 100644
--- a/src/uu/sort/src/sort.rs
+++ b/src/uu/sort/src/sort.rs
@@ -29,19 +29,22 @@ use custom_str_cmp::custom_str_cmp;
 use ext_sort::ext_sort;
 use fnv::FnvHasher;
 use numeric_str_cmp::{human_numeric_str_cmp, numeric_str_cmp, NumInfo, NumInfoParseSettings};
-use rand::distributions::Alphanumeric;
 use rand::{thread_rng, Rng};
 use rayon::prelude::*;
 use std::cmp::Ordering;
 use std::env;
-use std::ffi::OsStr;
-use std::fs::File;
+use std::error::Error;
+use std::ffi::{OsStr, OsString};
+use std::fmt::Display;
+use std::fs::{File, OpenOptions};
 use std::hash::{Hash, Hasher};
 use std::io::{stdin, stdout, BufRead, BufReader, BufWriter, Read, Write};
 use std::ops::Range;
 use std::path::Path;
 use std::path::PathBuf;
+use std::str::Utf8Error;
 use unicode_width::UnicodeWidthStr;
+use uucore::error::{set_exit_code, UCustomError, UResult, USimpleError, UUsageError};
 use uucore::parse_size::{parse_size, ParseSizeError};
 use uucore::version_cmp::version_cmp;
 use uucore::InvalidEncodingHandling;
@@ -121,6 +124,111 @@ const POSITIVE: char = '+';
 // available memory into consideration, instead of relying on this constant only.
 const DEFAULT_BUF_SIZE: usize = 1_000_000_000; // 1 GB
 
+#[derive(Debug)]
+enum SortError {
+    Disorder {
+        file: OsString,
+        line_number: usize,
+        line: String,
+        silent: bool,
+    },
+    OpenFailed {
+        path: String,
+        error: std::io::Error,
+    },
+    ReadFailed {
+        path: String,
+        error: std::io::Error,
+    },
+    ParseKeyError {
+        key: String,
+        msg: String,
+    },
+    OpenTmpFileFailed {
+        error: std::io::Error,
+    },
+    CompressProgExecutionFailed {
+        code: i32,
+    },
+    CompressProgTerminatedAbnormally {
+        prog: String,
+    },
+    TmpDirCreationFailed,
+    Uft8Error {
+        error: Utf8Error,
+    },
+}
+
+impl Error for SortError {}
+
+impl UCustomError for SortError {
+    fn code(&self) -> i32 {
+        match self {
+            SortError::Disorder { .. } => 1,
+            _ => 2,
+        }
+    }
+
+    fn usage(&self) -> bool {
+        false
+    }
+}
+
+impl Display for SortError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            SortError::Disorder {
+                file,
+                line_number,
+                line,
+                silent,
+            } => {
+                if !silent {
+                    write!(
+                        f,
+                        "{}:{}: disorder: {}",
+                        file.to_string_lossy(),
+                        line_number,
+                        line
+                    )
+                } else {
+                    Ok(())
+                }
+            }
+            SortError::OpenFailed { path, error } => write!(
+                f,
+                "open failed: {}: {}",
+                path,
+                strip_errno(&error.to_string())
+            ),
+            SortError::ParseKeyError { key, msg } => {
+                write!(f, "failed to parse key `{}`: {}", key, msg)
+            }
+            SortError::ReadFailed { path, error } => write!(
+                f,
+                "cannot read: {}: {}",
+                path,
+                strip_errno(&error.to_string())
+            ),
+            SortError::OpenTmpFileFailed { error } => {
+                write!(
+                    f,
+                    "failed to open temporary file: {}",
+                    strip_errno(&error.to_string())
+                )
+            }
+            SortError::CompressProgExecutionFailed { code } => {
+                write!(f, "couldn't execute compress program: errno {}", code)
+            }
+            SortError::CompressProgTerminatedAbnormally { prog } => {
+                write!(f, "'{}' terminated abnormally", prog)
+            }
+            SortError::TmpDirCreationFailed => write!(f, "could not create temporary directory"),
+            SortError::Uft8Error { error } => write!(f, "{}", error),
+        }
+    }
+}
+
 #[derive(Eq, Ord, PartialEq, PartialOrd, Clone, Copy, Debug)]
 enum SortMode {
     Numeric,
@@ -146,6 +254,49 @@ impl SortMode {
     }
 }
 
+pub struct Output {
+    file: Option<(String, File)>,
+}
+
+impl Output {
+    fn new(name: Option<&str>) -> UResult<Self> {
+        let file = if let Some(name) = name {
+            // This is different from `File::create()` because we don't truncate the output yet.
+            // This allows using the output file as an input file.
+            let file = OpenOptions::new()
+                .write(true)
+                .create(true)
+                .open(name)
+                .map_err(|e| SortError::OpenFailed {
+                    path: name.to_owned(),
+                    error: e,
+                })?;
+            Some((name.to_owned(), file))
+        } else {
+            None
+        };
+        Ok(Self { file })
+    }
+
+    fn into_write(self) -> BufWriter<Box<dyn Write>> {
+        BufWriter::new(match self.file {
+            Some((_name, file)) => {
+                // truncate the file
+                let _ = file.set_len(0);
+                Box::new(file)
+            }
+            None => Box::new(stdout()),
+        })
+    }
+
+    fn as_output_name(&self) -> Option<&str> {
+        match &self.file {
+            Some((name, _file)) => Some(name),
+            None => None,
+        }
+    }
+}
+
 #[derive(Clone)]
 pub struct GlobalSettings {
     mode: SortMode,
@@ -156,12 +307,11 @@ pub struct GlobalSettings {
     ignore_non_printing: bool,
     merge: bool,
     reverse: bool,
-    output_file: Option<String>,
     stable: bool,
     unique: bool,
     check: bool,
     check_silent: bool,
-    salt: String,
+    salt: Option<[u8; 16]>,
     selectors: Vec<FieldSelector>,
     separator: Option<char>,
     threads: String,
@@ -209,19 +359,6 @@ impl GlobalSettings {
         }
     }
 
-    fn out_writer(&self) -> BufWriter<Box<dyn Write>> {
-        match self.output_file {
-            Some(ref filename) => match File::create(Path::new(&filename)) {
-                Ok(f) => BufWriter::new(Box::new(f) as Box<dyn Write>),
-                Err(e) => {
-                    show_error!("{0}: {1}", filename, e.to_string());
-                    panic!("Could not open output file");
-                }
-            },
-            None => BufWriter::new(Box::new(stdout()) as Box<dyn Write>),
-        }
-    }
-
     /// Precompute some data needed for sorting.
     /// This function **must** be called before starting to sort, and `GlobalSettings` may not be altered
     /// afterwards.
@@ -253,12 +390,11 @@ impl Default for GlobalSettings {
             ignore_non_printing: false,
             merge: false,
             reverse: false,
-            output_file: None,
             stable: false,
             unique: false,
             check: false,
             check_silent: false,
-            salt: String::new(),
+            salt: None,
             selectors: vec![],
             separator: None,
             threads: String::new(),
@@ -697,33 +833,37 @@ impl FieldSelector {
         }
     }
 
-    fn parse(key: &str, global_settings: &GlobalSettings) -> Self {
+    fn parse(key: &str, global_settings: &GlobalSettings) -> UResult<Self> {
         let mut from_to = key.split(',');
         let (from, from_options) = Self::split_key_options(from_to.next().unwrap());
         let to = from_to.next().map(|to| Self::split_key_options(to));
         let options_are_empty = from_options.is_empty() && matches!(to, None | Some((_, "")));
-        crash_if_err!(
-            2,
-            if options_are_empty {
-                // Inherit the global settings if there are no options attached to this key.
-                (|| {
-                    // This would be ideal for a try block, I think. In the meantime this closure allows
-                    // to use the `?` operator here.
-                    Self::new(
-                        KeyPosition::new(from, 1, global_settings.ignore_leading_blanks)?,
-                        to.map(|(to, _)| {
-                            KeyPosition::new(to, 0, global_settings.ignore_leading_blanks)
-                        })
-                        .transpose()?,
-                        KeySettings::from(global_settings),
-                    )
-                })()
-            } else {
-                // Do not inherit from `global_settings`, as there are options attached to this key.
-                Self::parse_with_options((from, from_options), to)
+
+        if options_are_empty {
+            // Inherit the global settings if there are no options attached to this key.
+            (|| {
+                // This would be ideal for a try block, I think. In the meantime this closure allows
+                // to use the `?` operator here.
+                Self::new(
+                    KeyPosition::new(from, 1, global_settings.ignore_leading_blanks)?,
+                    to.map(|(to, _)| {
+                        KeyPosition::new(to, 0, global_settings.ignore_leading_blanks)
+                    })
+                    .transpose()?,
+                    KeySettings::from(global_settings),
+                )
+            })()
+        } else {
+            // Do not inherit from `global_settings`, as there are options attached to this key.
+            Self::parse_with_options((from, from_options), to)
+        }
+        .map_err(|msg| {
+            SortError::ParseKeyError {
+                key: key.to_owned(),
+                msg,
             }
-            .map_err(|e| format!("failed to parse key `{}`: {}", key, e))
-        )
+            .into()
+        })
     }
 
     fn parse_with_options(
@@ -916,9 +1056,7 @@ impl FieldSelector {
 
 fn get_usage() -> String {
     format!(
-        "{0}
-Usage:
- {0} [OPTION]... [FILE]...
+        "{0} [OPTION]... [FILE]...
 Write the sorted concatenation of all FILE(s) to standard output.
 Mandatory arguments for long options are mandatory for short options too.
 With no FILE, or when FILE is -, read standard input.",
@@ -937,41 +1075,57 @@ fn make_sort_mode_arg<'a, 'b>(mode: &'a str, short: &'b str, help: &'b str) -> A
     arg
 }
 
-pub fn uumain(args: impl uucore::Args) -> i32 {
+#[uucore_procs::gen_uumain]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let args = args
         .collect_str(InvalidEncodingHandling::Ignore)
         .accept_any();
     let usage = get_usage();
     let mut settings: GlobalSettings = Default::default();
 
-    let matches = uu_app().usage(&usage[..]).get_matches_from(args);
+    let matches = match uu_app().usage(&usage[..]).get_matches_from_safe(args) {
+        Ok(t) => t,
+        Err(e) => {
+            // not all clap "Errors" are because of a failure to parse arguments.
+            // "--version" also causes an Error to be returned, but we should not print to stderr
+            // nor return with a non-zero exit code in this case (we should print to stdout and return 0).
+            // This logic is similar to the code in clap, but we return 2 as the exit code in case of real failure
+            // (clap returns 1).
+            if e.use_stderr() {
+                eprintln!("{}", e.message);
+                set_exit_code(2);
+            } else {
+                println!("{}", e.message);
+            }
+            return Ok(());
+        }
+    };
 
     settings.debug = matches.is_present(options::DEBUG);
 
     // check whether user specified a zero terminated list of files for input, otherwise read files from args
-    let mut files: Vec<String> = if matches.is_present(options::FILES0_FROM) {
-        let files0_from: Vec<String> = matches
-            .values_of(options::FILES0_FROM)
-            .map(|v| v.map(ToString::to_string).collect())
+    let mut files: Vec<OsString> = if matches.is_present(options::FILES0_FROM) {
+        let files0_from: Vec<OsString> = matches
+            .values_of_os(options::FILES0_FROM)
+            .map(|v| v.map(ToOwned::to_owned).collect())
             .unwrap_or_default();
 
         let mut files = Vec::new();
         for path in &files0_from {
-            let reader = open(path.as_str());
+            let reader = open(&path)?;
             let buf_reader = BufReader::new(reader);
             for line in buf_reader.split(b'\0').flatten() {
-                files.push(
+                files.push(OsString::from(
                     std::str::from_utf8(&line)
-                        .expect("Could not parse string from zero terminated input.")
-                        .to_string(),
-                );
+                        .expect("Could not parse string from zero terminated input."),
+                ));
             }
         }
         files
     } else {
         matches
-            .values_of(options::FILES)
-            .map(|v| v.map(ToString::to_string).collect())
+            .values_of_os(options::FILES)
+            .map(|v| v.map(ToOwned::to_owned).collect())
             .unwrap_or_default()
     };
 
@@ -998,7 +1152,7 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
     } else if matches.is_present(options::modes::RANDOM)
         || matches.value_of(options::modes::SORT) == Some("random")
     {
-        settings.salt = get_rand_string();
+        settings.salt = Some(get_rand_string());
         SortMode::Random
     } else {
         SortMode::Default
@@ -1015,12 +1169,14 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
         env::set_var("RAYON_NUM_THREADS", &settings.threads);
     }
 
-    settings.buffer_size = matches
-        .value_of(options::BUF_SIZE)
-        .map_or(DEFAULT_BUF_SIZE, |s| {
-            GlobalSettings::parse_byte_count(s)
-                .unwrap_or_else(|e| crash!(2, "{}", format_error_message(e, s, options::BUF_SIZE)))
-        });
+    settings.buffer_size =
+        matches
+            .value_of(options::BUF_SIZE)
+            .map_or(Ok(DEFAULT_BUF_SIZE), |s| {
+                GlobalSettings::parse_byte_count(s).map_err(|e| {
+                    USimpleError::new(2, format_error_message(e, s, options::BUF_SIZE))
+                })
+            })?;
 
     settings.tmp_dir = matches
         .value_of(options::TMP_DIR)
@@ -1030,9 +1186,9 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
     settings.compress_prog = matches.value_of(options::COMPRESS_PROG).map(String::from);
 
     if let Some(n_merge) = matches.value_of(options::BATCH_SIZE) {
-        settings.merge_batch_size = n_merge
-            .parse()
-            .unwrap_or_else(|_| crash!(2, "invalid --batch-size argument '{}'", n_merge));
+        settings.merge_batch_size = n_merge.parse().map_err(|_| {
+            UUsageError::new(2, format!("invalid --batch-size argument '{}'", n_merge))
+        })?;
     }
 
     settings.zero_terminated = matches.is_present(options::ZERO_TERMINATED);
@@ -1053,32 +1209,45 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
 
     settings.ignore_leading_blanks = matches.is_present(options::IGNORE_LEADING_BLANKS);
 
-    settings.output_file = matches.value_of(options::OUTPUT).map(String::from);
     settings.reverse = matches.is_present(options::REVERSE);
     settings.stable = matches.is_present(options::STABLE);
     settings.unique = matches.is_present(options::UNIQUE);
 
     if files.is_empty() {
         /* if no file, default to stdin */
-        files.push("-".to_owned());
+        files.push("-".to_string().into());
     } else if settings.check && files.len() != 1 {
-        crash!(1, "extra operand `{}' not allowed with -c", files[1])
+        return Err(UUsageError::new(
+            2,
+            format!(
+                "extra operand `{}' not allowed with -c",
+                files[1].to_string_lossy()
+            ),
+        ));
     }
 
     if let Some(arg) = matches.args.get(options::SEPARATOR) {
         let separator = arg.vals[0].to_string_lossy();
-        let separator = separator;
+        let mut separator = separator.as_ref();
+        if separator == "\\0" {
+            separator = "\0";
+        }
         if separator.len() != 1 {
-            crash!(1, "separator must be exactly one character long");
+            return Err(UUsageError::new(
+                2,
+                "separator must be exactly one character long".into(),
+            ));
         }
         settings.separator = Some(separator.chars().next().unwrap())
     }
 
     if let Some(values) = matches.values_of(options::KEY) {
         for value in values {
-            settings
-                .selectors
-                .push(FieldSelector::parse(value, &settings));
+            let selector = FieldSelector::parse(value, &settings)?;
+            if selector.settings.mode == SortMode::Random && settings.salt.is_none() {
+                settings.salt = Some(get_rand_string());
+            }
+            settings.selectors.push(selector);
         }
     }
 
@@ -1099,9 +1268,19 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
         );
     }
 
+    // Verify that we can open all input files.
+    // It is the correct behavior to close all files afterwards,
+    // and to reopen them at a later point. This is different from how the output file is handled,
+    // probably to prevent running out of file descriptors.
+    for file in &files {
+        open(file)?;
+    }
+
+    let output = Output::new(matches.value_of(options::OUTPUT))?;
+
     settings.init_precomputed();
 
-    exec(&files, &settings)
+    exec(&mut files, &settings, output)
 }
 
 pub fn uu_app() -> App<'static, 'static> {
@@ -1112,73 +1291,57 @@ pub fn uu_app() -> App<'static, 'static> {
             Arg::with_name(options::modes::SORT)
                 .long(options::modes::SORT)
                 .takes_value(true)
-                .possible_values(
-                    &[
-                        "general-numeric",
-                        "human-numeric",
-                        "month",
-                        "numeric",
-                        "version",
-                        "random",
-                    ]
-                )
-                .conflicts_with_all(&options::modes::ALL_SORT_MODES)
-        )
-        .arg(
-            make_sort_mode_arg(
-                options::modes::HUMAN_NUMERIC,
-                "h",
-                "compare according to human readable sizes, eg 1M > 100k"
-            ),
-        )
-        .arg(
-            make_sort_mode_arg(
-                options::modes::MONTH,
-                "M",
-                "compare according to month name abbreviation"
-            ),
-        )
-        .arg(
-            make_sort_mode_arg(
-                options::modes::NUMERIC,
-                "n",
-                "compare according to string numerical value"
-            ),
-        )
-        .arg(
-            make_sort_mode_arg(
-                options::modes::GENERAL_NUMERIC,
-                "g",
-                "compare according to string general numerical value"
-            ),
-        )
-        .arg(
-            make_sort_mode_arg(
-                options::modes::VERSION,
-                "V",
-                "Sort by SemVer version number, eg 1.12.2 > 1.1.2",
-            ),
-        )
-        .arg(
-            make_sort_mode_arg(
-                options::modes::RANDOM,
-                "R",
-                "shuffle in random order",
-            ),
+                .possible_values(&[
+                    "general-numeric",
+                    "human-numeric",
+                    "month",
+                    "numeric",
+                    "version",
+                    "random",
+                ])
+                .conflicts_with_all(&options::modes::ALL_SORT_MODES),
         )
+        .arg(make_sort_mode_arg(
+            options::modes::HUMAN_NUMERIC,
+            "h",
+            "compare according to human readable sizes, eg 1M > 100k",
+        ))
+        .arg(make_sort_mode_arg(
+            options::modes::MONTH,
+            "M",
+            "compare according to month name abbreviation",
+        ))
+        .arg(make_sort_mode_arg(
+            options::modes::NUMERIC,
+            "n",
+            "compare according to string numerical value",
+        ))
+        .arg(make_sort_mode_arg(
+            options::modes::GENERAL_NUMERIC,
+            "g",
+            "compare according to string general numerical value",
+        ))
+        .arg(make_sort_mode_arg(
+            options::modes::VERSION,
+            "V",
+            "Sort by SemVer version number, eg 1.12.2 > 1.1.2",
+        ))
+        .arg(make_sort_mode_arg(
+            options::modes::RANDOM,
+            "R",
+            "shuffle in random order",
+        ))
         .arg(
             Arg::with_name(options::DICTIONARY_ORDER)
                 .short("d")
                 .long(options::DICTIONARY_ORDER)
                 .help("consider only blanks and alphanumeric characters")
-                .conflicts_with_all(
-                    &[
-                        options::modes::NUMERIC,
-                        options::modes::GENERAL_NUMERIC,
-                        options::modes::HUMAN_NUMERIC,
-                        options::modes::MONTH,
-                    ]
-                ),
+                .conflicts_with_all(&[
+                    options::modes::NUMERIC,
+                    options::modes::GENERAL_NUMERIC,
+                    options::modes::HUMAN_NUMERIC,
+                    options::modes::MONTH,
+                ]),
         )
         .arg(
             Arg::with_name(options::MERGE)
@@ -1206,7 +1369,10 @@ pub fn uu_app() -> App<'static, 'static> {
                 .short("C")
                 .long(options::check::CHECK_SILENT)
                 .conflicts_with(options::OUTPUT)
-                .help("exit successfully if the given file is already sorted, and exit with status 1 otherwise."),
+                .help(
+                    "exit successfully if the given file is already sorted,\
+                and exit with status 1 otherwise.",
+                ),
         )
         .arg(
             Arg::with_name(options::IGNORE_CASE)
@@ -1219,14 +1385,12 @@ pub fn uu_app() -> App<'static, 'static> {
                 .short("i")
                 .long(options::IGNORE_NONPRINTING)
                 .help("ignore nonprinting characters")
-                .conflicts_with_all(
-                    &[
-                        options::modes::NUMERIC,
-                        options::modes::GENERAL_NUMERIC,
-                        options::modes::HUMAN_NUMERIC,
-                        options::modes::MONTH
-                    ]
-                ),
+                .conflicts_with_all(&[
+                    options::modes::NUMERIC,
+                    options::modes::GENERAL_NUMERIC,
+                    options::modes::HUMAN_NUMERIC,
+                    options::modes::MONTH,
+                ]),
         )
         .arg(
             Arg::with_name(options::IGNORE_LEADING_BLANKS)
@@ -1275,7 +1439,8 @@ pub fn uu_app() -> App<'static, 'static> {
                 .short("t")
                 .long(options::SEPARATOR)
                 .help("custom separator for -k")
-                .takes_value(true))
+                .takes_value(true),
+        )
         .arg(
             Arg::with_name(options::ZERO_TERMINATED)
                 .short("z")
@@ -1310,13 +1475,13 @@ pub fn uu_app() -> App<'static, 'static> {
                 .long(options::COMPRESS_PROG)
                 .help("compress temporary files with PROG, decompress with PROG -d")
                 .long_help("PROG has to take input from stdin and output to stdout")
-                .value_name("PROG")
+                .value_name("PROG"),
         )
         .arg(
             Arg::with_name(options::BATCH_SIZE)
                 .long(options::BATCH_SIZE)
                 .help("Merge at most N_MERGE inputs at once.")
-                .value_name("N_MERGE")
+                .value_name("N_MERGE"),
         )
         .arg(
             Arg::with_name(options::FILES0_FROM)
@@ -1331,24 +1496,27 @@ pub fn uu_app() -> App<'static, 'static> {
                 .long(options::DEBUG)
                 .help("underline the parts of the line that are actually used for sorting"),
         )
-        .arg(Arg::with_name(options::FILES).multiple(true).takes_value(true))
+        .arg(
+            Arg::with_name(options::FILES)
+                .multiple(true)
+                .takes_value(true),
+        )
 }
 
-fn exec(files: &[String], settings: &GlobalSettings) -> i32 {
+fn exec(files: &mut [OsString], settings: &GlobalSettings, output: Output) -> UResult<()> {
     if settings.merge {
-        let mut file_merger = merge::merge(files.iter().map(open), settings);
-        file_merger.write_all(settings);
+        let file_merger = merge::merge(files, settings, output.as_output_name())?;
+        file_merger.write_all(settings, output)
     } else if settings.check {
         if files.len() > 1 {
-            crash!(1, "only one file allowed with -c");
+            Err(UUsageError::new(2, "only one file allowed with -c".into()))
+        } else {
+            check::check(files.first().unwrap(), settings)
         }
-        return check::check(files.first().unwrap(), settings);
     } else {
         let mut lines = files.iter().map(open);
-
-        ext_sort(&mut lines, settings);
+        ext_sort(&mut lines, settings, output)
     }
-    0
 }
 
 fn sort_by<'a>(unsorted: &mut Vec<Line<'a>>, settings: &GlobalSettings, line_data: &LineData<'a>) {
@@ -1387,7 +1555,22 @@ fn compare_by<'a>(
         let settings = &selector.settings;
 
         let cmp: Ordering = match settings.mode {
-            SortMode::Random => random_shuffle(a_str, b_str, &global_settings.salt),
+            SortMode::Random => {
+                // check if the two strings are equal
+                if custom_str_cmp(
+                    a_str,
+                    b_str,
+                    settings.ignore_non_printing,
+                    settings.dictionary_order,
+                    settings.ignore_case,
+                ) == Ordering::Equal
+                {
+                    Ordering::Equal
+                } else {
+                    // Only if they are not equal compare by the hash
+                    random_shuffle(a_str, b_str, &global_settings.salt.unwrap())
+                }
+            }
             SortMode::Numeric => {
                 let a_num_info = &a_line_data.num_infos
                     [a.index * global_settings.precomputed.num_infos_per_line + num_info_index];
@@ -1536,12 +1719,8 @@ fn general_numeric_compare(a: &GeneralF64ParseResult, b: &GeneralF64ParseResult)
     a.partial_cmp(b).unwrap()
 }
 
-fn get_rand_string() -> String {
-    thread_rng()
-        .sample_iter(&Alphanumeric)
-        .take(16)
-        .map(char::from)
-        .collect::<String>()
+fn get_rand_string() -> [u8; 16] {
+    thread_rng().sample(rand::distributions::Standard)
 }
 
 fn get_hash<T: Hash>(t: &T) -> u64 {
@@ -1550,10 +1729,9 @@ fn get_hash<T: Hash>(t: &T) -> u64 {
     s.finish()
 }
 
-fn random_shuffle(a: &str, b: &str, salt: &str) -> Ordering {
-    let da = get_hash(&[a, salt].concat());
-    let db = get_hash(&[b, salt].concat());
-
+fn random_shuffle(a: &str, b: &str, salt: &[u8]) -> Ordering {
+    let da = get_hash(&(a, salt));
+    let db = get_hash(&(b, salt));
     da.cmp(&db)
 }
 
@@ -1618,26 +1796,38 @@ fn month_compare(a: &str, b: &str) -> Ordering {
     }
 }
 
-fn print_sorted<'a, T: Iterator<Item = &'a Line<'a>>>(iter: T, settings: &GlobalSettings) {
-    let mut writer = settings.out_writer();
+fn print_sorted<'a, T: Iterator<Item = &'a Line<'a>>>(
+    iter: T,
+    settings: &GlobalSettings,
+    output: Output,
+) {
+    let mut writer = output.into_write();
     for line in iter {
         line.print(&mut writer, settings);
     }
 }
 
-// from cat.rs
-fn open(path: impl AsRef<OsStr>) -> Box<dyn Read + Send> {
+/// Strips the trailing " (os error XX)" from io error strings.
+fn strip_errno(err: &str) -> &str {
+    &err[..err.find(" (os error ").unwrap_or(err.len())]
+}
+
+fn open(path: impl AsRef<OsStr>) -> UResult<Box<dyn Read + Send>> {
     let path = path.as_ref();
     if path == "-" {
         let stdin = stdin();
-        return Box::new(stdin) as Box<dyn Read + Send>;
+        return Ok(Box::new(stdin) as Box<dyn Read + Send>);
     }
 
-    match File::open(Path::new(path)) {
-        Ok(f) => Box::new(f) as Box<dyn Read + Send>,
-        Err(e) => {
-            crash!(2, "cannot read: {0:?}: {1}", path, e);
+    let path = Path::new(path);
+
+    match File::open(path) {
+        Ok(f) => Ok(Box::new(f) as Box<dyn Read + Send>),
+        Err(error) => Err(SortError::ReadFailed {
+            path: path.to_string_lossy().to_string(),
+            error,
         }
+        .into()),
     }
 }
 
diff --git a/src/uu/stat/src/stat.rs b/src/uu/stat/src/stat.rs
index 70c06bdf6..c56971f6b 100644
--- a/src/uu/stat/src/stat.rs
+++ b/src/uu/stat/src/stat.rs
@@ -436,6 +436,7 @@ impl Stater {
                             'f' => tokens.push(Token::Char('\x0C')),
                             'n' => tokens.push(Token::Char('\n')),
                             'r' => tokens.push(Token::Char('\r')),
+                            't' => tokens.push(Token::Char('\t')),
                             'v' => tokens.push(Token::Char('\x0B')),
                             c => {
                                 show_warning!("unrecognized escape '\\{}'", c);
diff --git a/src/uu/tac/src/tac.rs b/src/uu/tac/src/tac.rs
index ae1fd9bc5..407228e36 100644
--- a/src/uu/tac/src/tac.rs
+++ b/src/uu/tac/src/tac.rs
@@ -97,7 +97,7 @@ fn tac(filenames: Vec<String>, before: bool, _: bool, separator: &str) -> i32 {
             let path = Path::new(filename);
             if path.is_dir() || path.metadata().is_err() {
                 if path.is_dir() {
-                    show_error!("dir: read error: Invalid argument");
+                    show_error!("{}: read error: Invalid argument", filename);
                 } else {
                     show_error!(
                         "failed to open '{}' for reading: No such file or directory",
@@ -139,9 +139,16 @@ fn tac(filenames: Vec<String>, before: bool, _: bool, separator: &str) -> i32 {
                 i += 1;
             }
         }
+        // If the file contains no line separators, then simply write
+        // the contents of the file directly to stdout.
+        if offsets.is_empty() {
+            out.write_all(&data)
+                .unwrap_or_else(|e| crash!(1, "failed to write to stdout: {}", e));
+            return exit_code;
+        }
 
         // if there isn't a separator at the end of the file, fake it
-        if offsets.is_empty() || *offsets.last().unwrap() < data.len() - slen {
+        if *offsets.last().unwrap() < data.len() - slen {
             offsets.push(data.len());
         }
 
diff --git a/src/uu/tail/Cargo.toml b/src/uu/tail/Cargo.toml
index bab6c125d..710a1421f 100644
--- a/src/uu/tail/Cargo.toml
+++ b/src/uu/tail/Cargo.toml
@@ -24,6 +24,10 @@ winapi = { version="0.3", features=["fileapi", "handleapi", "processthreadsapi",
 [target.'cfg(target_os = "redox")'.dependencies]
 redox_syscall = "0.1"
 
+[target.'cfg(unix)'.dependencies]
+nix = "0.20"
+libc = "0.2"
+
 [[bin]]
 name = "tail"
 path = "src/main.rs"
diff --git a/src/uu/tail/README.md b/src/uu/tail/README.md
index b7f92f8e4..94b6816af 100644
--- a/src/uu/tail/README.md
+++ b/src/uu/tail/README.md
@@ -11,7 +11,7 @@
 
 ### Others
 
-- [ ] The current implementation does not handle `-` as an alias for stdin.
+- [ ] The current implementation doesn't follow stdin in non-unix platforms
 
 ## Possible optimizations
 
diff --git a/src/uu/tail/src/platform/mod.rs b/src/uu/tail/src/platform/mod.rs
index 010c5c4ac..4a8982713 100644
--- a/src/uu/tail/src/platform/mod.rs
+++ b/src/uu/tail/src/platform/mod.rs
@@ -2,13 +2,14 @@
  * This file is part of the uutils coreutils package.
  *
  * (c) Alexander Batischev <eual.jp@gmail.com>
+ * (c) Thomas Queiroz <thomasqueirozb@gmail.com>
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
 
 #[cfg(unix)]
-pub use self::unix::{supports_pid_checks, Pid, ProcessChecker};
+pub use self::unix::{stdin_is_pipe_or_fifo, supports_pid_checks, Pid, ProcessChecker};
 
 #[cfg(windows)]
 pub use self::windows::{supports_pid_checks, Pid, ProcessChecker};
diff --git a/src/uu/tail/src/platform/unix.rs b/src/uu/tail/src/platform/unix.rs
index 167f693e6..580a40135 100644
--- a/src/uu/tail/src/platform/unix.rs
+++ b/src/uu/tail/src/platform/unix.rs
@@ -2,6 +2,7 @@
  * This file is part of the uutils coreutils package.
  *
  * (c) Alexander Batischev <eual.jp@gmail.com>
+ * (c) Thomas Queiroz <thomasqueirozb@gmail.com>
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -9,7 +10,13 @@
 
 // spell-checker:ignore (ToDO) errno EPERM ENOSYS
 
-use std::io::Error;
+use std::io::{stdin, Error};
+
+use std::os::unix::prelude::AsRawFd;
+
+use nix::sys::stat::fstat;
+
+use libc::{S_IFIFO, S_IFSOCK};
 
 pub type Pid = libc::pid_t;
 
@@ -40,3 +47,16 @@ pub fn supports_pid_checks(pid: self::Pid) -> bool {
 fn get_errno() -> i32 {
     Error::last_os_error().raw_os_error().unwrap()
 }
+
+pub fn stdin_is_pipe_or_fifo() -> bool {
+    let fd = stdin().lock().as_raw_fd();
+    fd >= 0 // GNU tail checks fd >= 0
+                            && match fstat(fd) {
+                                Ok(stat) => {
+                                    let mode = stat.st_mode;
+                                    // NOTE: This is probably not the most correct way to check this
+                                    (mode & S_IFIFO != 0) || (mode & S_IFSOCK != 0)
+                                }
+                                Err(err) => panic!("{}", err),
+                            }
+}
diff --git a/src/uu/tail/src/tail.rs b/src/uu/tail/src/tail.rs
index 4970cdcc2..471c1a404 100644
--- a/src/uu/tail/src/tail.rs
+++ b/src/uu/tail/src/tail.rs
@@ -2,6 +2,7 @@
 //  *
 //  * (c) Morten Olsen Lysgaard <morten@lysgaard.no>
 //  * (c) Alexander Batischev <eual.jp@gmail.com>
+//  * (c) Thomas Queiroz <thomasqueirozb@gmail.com>
 //  *
 //  * For the full copyright and license information, please view the LICENSE
 //  * file that was distributed with this source code.
@@ -29,6 +30,9 @@ use std::time::Duration;
 use uucore::parse_size::{parse_size, ParseSizeError};
 use uucore::ringbuffer::RingBuffer;
 
+#[cfg(unix)]
+use crate::platform::stdin_is_pipe_or_fifo;
+
 pub mod options {
     pub mod verbosity {
         pub static QUIET: &str = "quiet";
@@ -130,25 +134,56 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
     let files: Vec<String> = matches
         .values_of(options::ARG_FILES)
         .map(|v| v.map(ToString::to_string).collect())
-        .unwrap_or_default();
+        .unwrap_or_else(|| vec![String::from("-")]);
 
-    if files.is_empty() {
-        let mut buffer = BufReader::new(stdin());
-        unbounded_tail(&mut buffer, &settings);
-    } else {
-        let multiple = files.len() > 1;
-        let mut first_header = true;
-        let mut readers = Vec::new();
+    let multiple = files.len() > 1;
+    let mut first_header = true;
+    let mut readers: Vec<(Box<dyn BufRead>, &String)> = Vec::new();
 
-        for filename in &files {
-            if (multiple || verbose) && !quiet {
-                if !first_header {
-                    println!();
-                }
+    #[cfg(unix)]
+    let stdin_string = String::from("standard input");
+
+    for filename in &files {
+        let use_stdin = filename.as_str() == "-";
+        if (multiple || verbose) && !quiet {
+            if !first_header {
+                println!();
+            }
+            if use_stdin {
+                println!("==> standard input <==");
+            } else {
                 println!("==> {} <==", filename);
             }
-            first_header = false;
+        }
+        first_header = false;
 
+        if use_stdin {
+            let mut reader = BufReader::new(stdin());
+            unbounded_tail(&mut reader, &settings);
+
+            // Don't follow stdin since there are no checks for pipes/FIFOs
+            //
+            // FIXME windows has GetFileType which can determine if the file is a pipe/FIFO
+            // so this check can also be performed
+
+            #[cfg(unix)]
+            {
+                /*
+                POSIX specification regarding tail -f
+
+                If the input file is a regular file or if the file operand specifies a FIFO, do not
+                terminate after the last line of the input file has been copied, but read and copy
+                further bytes from the input file when they become available. If no file operand is
+                specified and standard input is a pipe or FIFO, the -f option shall be ignored. If
+                the input file is not a FIFO, pipe, or regular file, it is unspecified whether or
+                not the -f option shall be ignored.
+                */
+
+                if settings.follow && !stdin_is_pipe_or_fifo() {
+                    readers.push((Box::new(reader), &stdin_string));
+                }
+            }
+        } else {
             let path = Path::new(filename);
             if path.is_dir() {
                 continue;
@@ -158,20 +193,20 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
                 bounded_tail(&mut file, &settings);
                 if settings.follow {
                     let reader = BufReader::new(file);
-                    readers.push(reader);
+                    readers.push((Box::new(reader), filename));
                 }
             } else {
                 let mut reader = BufReader::new(file);
                 unbounded_tail(&mut reader, &settings);
                 if settings.follow {
-                    readers.push(reader);
+                    readers.push((Box::new(reader), filename));
                 }
             }
         }
+    }
 
-        if settings.follow {
-            follow(&mut readers[..], &files[..], &settings);
-        }
+    if settings.follow {
+        follow(&mut readers[..], &settings);
     }
 
     0
@@ -248,8 +283,12 @@ pub fn uu_app() -> App<'static, 'static> {
         )
 }
 
-fn follow<T: Read>(readers: &mut [BufReader<T>], filenames: &[String], settings: &Settings) {
+fn follow<T: BufRead>(readers: &mut [(T, &String)], settings: &Settings) {
     assert!(settings.follow);
+    if readers.is_empty() {
+        return;
+    }
+
     let mut last = readers.len() - 1;
     let mut read_some = false;
     let mut process = platform::ProcessChecker::new(settings.pid);
@@ -260,7 +299,7 @@ fn follow<T: Read>(readers: &mut [BufReader<T>], filenames: &[String], settings:
         let pid_is_dead = !read_some && settings.pid != 0 && process.is_dead();
         read_some = false;
 
-        for (i, reader) in readers.iter_mut().enumerate() {
+        for (i, (reader, filename)) in readers.iter_mut().enumerate() {
             // Print all new content since the last pass
             loop {
                 let mut datum = String::new();
@@ -269,7 +308,7 @@ fn follow<T: Read>(readers: &mut [BufReader<T>], filenames: &[String], settings:
                     Ok(_) => {
                         read_some = true;
                         if i != last {
-                            println!("\n==> {} <==", filenames[i]);
+                            println!("\n==> {} <==", filename);
                             last = i;
                         }
                         print!("{}", datum);
diff --git a/src/uu/touch/src/touch.rs b/src/uu/touch/src/touch.rs
index bfc7a4197..dd2b05d0e 100644
--- a/src/uu/touch/src/touch.rs
+++ b/src/uu/touch/src/touch.rs
@@ -8,9 +8,6 @@
 
 // spell-checker:ignore (ToDO) filetime strptime utcoff strs datetime MMDDhhmm
 
-// clippy bug https://github.com/rust-lang/rust-clippy/issues/7422
-#![allow(clippy::nonstandard_macro_braces)]
-
 pub extern crate filetime;
 
 #[macro_use]
diff --git a/src/uu/true/src/true.rs b/src/uu/true/src/true.rs
index ea53b0075..f84a89176 100644
--- a/src/uu/true/src/true.rs
+++ b/src/uu/true/src/true.rs
@@ -5,12 +5,17 @@
 //  * For the full copyright and license information, please view the LICENSE
 //  * file that was distributed with this source code.
 
+#[macro_use]
+extern crate uucore;
+
 use clap::App;
+use uucore::error::UResult;
 use uucore::executable;
 
-pub fn uumain(args: impl uucore::Args) -> i32 {
+#[uucore_procs::gen_uumain]
+pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     uu_app().get_matches_from(args);
-    0
+    Ok(())
 }
 
 pub fn uu_app() -> App<'static, 'static> {
diff --git a/src/uu/wc/src/wc.rs b/src/uu/wc/src/wc.rs
index 95d71e77a..0bcc66664 100644
--- a/src/uu/wc/src/wc.rs
+++ b/src/uu/wc/src/wc.rs
@@ -4,8 +4,6 @@
 //  *
 //  * For the full copyright and license information, please view the LICENSE
 //  * file that was distributed with this source code.
-// clippy bug https://github.com/rust-lang/rust-clippy/issues/7422
-#![allow(clippy::nonstandard_macro_braces)]
 
 #[macro_use]
 extern crate uucore;
diff --git a/src/uucore/Cargo.toml b/src/uucore/Cargo.toml
index 9ded42bbd..d62d89393 100644
--- a/src/uucore/Cargo.toml
+++ b/src/uucore/Cargo.toml
@@ -30,6 +30,10 @@ time = { version="<= 0.1.43", optional=true }
 data-encoding = { version="~2.1", optional=true } ## data-encoding: require v2.1; but v2.2.0 breaks the build for MinSRV v1.31.0
 libc = { version="0.2.15, <= 0.2.85", optional=true } ## libc: initial utmp support added in v0.2.15; but v0.2.68 breaks the build for MinSRV v1.31.0
 
+[dev-dependencies]
+clap = "2.33.3"
+lazy_static = "1.3"
+
 [target.'cfg(target_os = "windows")'.dependencies]
 winapi = { version = "0.3", features = ["errhandlingapi", "fileapi", "handleapi", "winerror"] }
 
diff --git a/src/uucore/src/lib/features/encoding.rs b/src/uucore/src/lib/features/encoding.rs
index 08c0d27e9..03fa0ed8b 100644
--- a/src/uucore/src/lib/features/encoding.rs
+++ b/src/uucore/src/lib/features/encoding.rs
@@ -7,9 +7,6 @@
 
 // spell-checker:ignore (strings) ABCDEFGHIJKLMNOPQRSTUVWXYZ
 
-// clippy bug https://github.com/rust-lang/rust-clippy/issues/7422
-#![allow(clippy::nonstandard_macro_braces)]
-
 extern crate data_encoding;
 
 use self::data_encoding::{DecodeError, BASE32, BASE64};
diff --git a/src/uucore/src/lib/mods/backup_control.rs b/src/uucore/src/lib/mods/backup_control.rs
index b8f389c83..6fa48d308 100644
--- a/src/uucore/src/lib/mods/backup_control.rs
+++ b/src/uucore/src/lib/mods/backup_control.rs
@@ -7,19 +7,15 @@ pub static BACKUP_CONTROL_VALUES: &[&str] = &[
     "simple", "never", "numbered", "t", "existing", "nil", "none", "off",
 ];
 
-pub static BACKUP_CONTROL_LONG_HELP: &str = "The backup suffix is '~', unless set with --suffix or SIMPLE_BACKUP_SUFFIX. Here are the version control values:
+pub static BACKUP_CONTROL_LONG_HELP: &str =
+    "The backup suffix is '~', unless set with --suffix or SIMPLE_BACKUP_SUFFIX.
+The version control method may be selected via the --backup option or through
+the VERSION_CONTROL environment variable.  Here are the values:
 
-none, off
-    never make backups (even if --backup is given)
-
-numbered, t
-    make numbered backups
-
-existing, nil
-    numbered if numbered backups exist, simple otherwise
-
-simple, never
-    always make simple backups";
+  none, off       never make backups (even if --backup is given)
+  numbered, t     make numbered backups
+  existing, nil   numbered if numbered backups exist, simple otherwise
+  simple, never   always make simple backups";
 
 #[derive(Debug, Clone, Copy, Eq, PartialEq)]
 pub enum BackupMode {
@@ -37,35 +33,177 @@ pub fn determine_backup_suffix(supplied_suffix: Option<&str>) -> String {
     }
 }
 
-/// # TODO
+/// Determine the "mode" for the backup operation to perform, if any.
 ///
-/// This function currently deviates slightly from how the [manual][1] describes
-/// that it should work. In particular, the current implementation:
+/// Parses the backup options according to the [GNU manual][1], and converts
+/// them to an instance of `BackupMode` for further processing.
 ///
-/// 1. Doesn't strictly respect the order in which to determine the backup type,
-///    which is (in order of precedence)
-///     1. Take a valid value to the '--backup' option
-///     2. Take the value of the `VERSION_CONTROL` env var
-///     3. default to 'existing'
-/// 2. Doesn't accept abbreviations to the 'backup_option' parameter
+/// For an explanation of what the arguments mean, refer to the examples below.
 ///
 /// [1]: https://www.gnu.org/software/coreutils/manual/html_node/Backup-options.html
-pub fn determine_backup_mode(backup_opt_exists: bool, backup_opt: Option<&str>) -> BackupMode {
-    if backup_opt_exists {
-        match backup_opt.map(String::from) {
-            // default is existing, see:
-            // https://www.gnu.org/software/coreutils/manual/html_node/Backup-options.html
-            None => BackupMode::ExistingBackup,
-            Some(mode) => match &mode[..] {
-                "simple" | "never" => BackupMode::SimpleBackup,
-                "numbered" | "t" => BackupMode::NumberedBackup,
-                "existing" | "nil" => BackupMode::ExistingBackup,
-                "none" | "off" => BackupMode::NoBackup,
-                _ => panic!(), // cannot happen as it is managed by clap
-            },
+///
+///
+/// # Errors
+///
+/// If an argument supplied directly to the long `backup` option, or read in
+/// through the `VERSION CONTROL` env var is ambiguous (i.e. may resolve to
+/// multiple backup modes) or invalid, an error is returned. The error contains
+/// the formatted error string which may then be passed to the
+/// [`show_usage_error`] macro.
+///
+///
+/// # Examples
+///
+/// Here's how one would integrate the backup mode determination into an
+/// application.
+///
+/// ```
+/// #[macro_use]
+/// extern crate uucore;
+/// use uucore::backup_control::{self, BackupMode};
+/// use clap::{App, Arg};
+///
+/// fn main() {
+///     let OPT_BACKUP: &str = "backup";
+///     let OPT_BACKUP_NO_ARG: &str = "b";
+///     let matches = App::new("app")
+///         .arg(Arg::with_name(OPT_BACKUP_NO_ARG)
+///             .short(OPT_BACKUP_NO_ARG))
+///         .arg(Arg::with_name(OPT_BACKUP)
+///             .long(OPT_BACKUP)
+///             .takes_value(true)
+///             .require_equals(true)
+///             .min_values(0))
+///         .get_matches_from(vec![
+///             "app", "-b", "--backup=t"
+///         ]);
+///    
+///     let backup_mode = backup_control::determine_backup_mode(
+///         matches.is_present(OPT_BACKUP_NO_ARG), matches.is_present(OPT_BACKUP),
+///         matches.value_of(OPT_BACKUP)
+///     );
+///     let backup_mode = match backup_mode {
+///         Err(err) => {
+///             show_usage_error!("{}", err);
+///             return;
+///         },
+///         Ok(mode) => mode,
+///     };
+/// }
+/// ```
+///
+/// This example shows an ambiguous input, as 'n' may resolve to 4 different
+/// backup modes.
+///
+///
+/// ```
+/// #[macro_use]
+/// extern crate uucore;
+/// use uucore::backup_control::{self, BackupMode};
+/// use clap::{crate_version, App, Arg, ArgMatches};
+///
+/// fn main() {
+///     let OPT_BACKUP: &str = "backup";
+///     let OPT_BACKUP_NO_ARG: &str = "b";
+///     let matches = App::new("app")
+///         .arg(Arg::with_name(OPT_BACKUP_NO_ARG)
+///             .short(OPT_BACKUP_NO_ARG))
+///         .arg(Arg::with_name(OPT_BACKUP)
+///             .long(OPT_BACKUP)
+///             .takes_value(true)
+///             .require_equals(true)
+///             .min_values(0))
+///         .get_matches_from(vec![
+///             "app", "-b", "--backup=n"
+///         ]);
+///    
+///     let backup_mode = backup_control::determine_backup_mode(
+///         matches.is_present(OPT_BACKUP_NO_ARG), matches.is_present(OPT_BACKUP),
+///         matches.value_of(OPT_BACKUP)
+///     );
+///     let backup_mode = match backup_mode {
+///         Err(err) => {
+///             show_usage_error!("{}", err);
+///             return;
+///         },
+///         Ok(mode) => mode,
+///     };
+/// }
+/// ```
+pub fn determine_backup_mode(
+    short_opt_present: bool,
+    long_opt_present: bool,
+    long_opt_value: Option<&str>,
+) -> Result<BackupMode, String> {
+    if long_opt_present {
+        // Use method to determine the type of backups to make. When this option
+        // is used but method is not specified, then the value of the
+        // VERSION_CONTROL environment variable is used. And if VERSION_CONTROL
+        // is not set, the default backup type is ‘existing’.
+        if let Some(method) = long_opt_value {
+            // Second argument is for the error string that is returned.
+            match_method(method, "backup type")
+        } else if let Ok(method) = env::var("VERSION_CONTROL") {
+            // Second argument is for the error string that is returned.
+            match_method(&method, "$VERSION_CONTROL")
+        } else {
+            Ok(BackupMode::ExistingBackup)
+        }
+    } else if short_opt_present {
+        // the short form of this option, -b does not accept any argument.
+        // Using -b is equivalent to using --backup=existing.
+        Ok(BackupMode::ExistingBackup)
+    } else {
+        // No option was present at all
+        Ok(BackupMode::NoBackup)
+    }
+}
+
+/// Match a backup option string to a `BackupMode`.
+///
+/// The GNU manual specifies that abbreviations to options are valid as long as
+/// they aren't ambiguous. This function matches the given `method` argument
+/// against all valid backup options (via `starts_with`), and returns a valid
+/// [`BackupMode`] if exactly one backup option matches the `method` given.
+///
+/// `origin` is required in order to format the generated error message
+/// properly, when an error occurs.
+///
+///
+/// # Errors
+///
+/// If `method` is ambiguous (i.e. may resolve to multiple backup modes) or
+/// invalid, an error is returned. The error contains the formatted error string
+/// which may then be passed to the [`show_usage_error`] macro.
+fn match_method(method: &str, origin: &str) -> Result<BackupMode, String> {
+    let matches: Vec<&&str> = BACKUP_CONTROL_VALUES
+        .iter()
+        .filter(|val| val.starts_with(method))
+        .collect();
+    if matches.len() == 1 {
+        match *matches[0] {
+            "simple" | "never" => Ok(BackupMode::SimpleBackup),
+            "numbered" | "t" => Ok(BackupMode::NumberedBackup),
+            "existing" | "nil" => Ok(BackupMode::ExistingBackup),
+            "none" | "off" => Ok(BackupMode::NoBackup),
+            _ => unreachable!(), // cannot happen as we must have exactly one match
+                                 // from the list above.
         }
     } else {
-        BackupMode::NoBackup
+        let error_type = if matches.is_empty() {
+            "invalid"
+        } else {
+            "ambiguous"
+        };
+        Err(format!(
+            "{0} argument ‘{1}’ for ‘{2}’
+Valid arguments are:
+  - ‘none’, ‘off’
+  - ‘simple’, ‘never’
+  - ‘existing’, ‘nil’
+  - ‘numbered’, ‘t’",
+            error_type, method, origin
+        ))
     }
 }
 
@@ -82,13 +220,13 @@ pub fn get_backup_path(
     }
 }
 
-pub fn simple_backup_path(path: &Path, suffix: &str) -> PathBuf {
+fn simple_backup_path(path: &Path, suffix: &str) -> PathBuf {
     let mut p = path.to_string_lossy().into_owned();
     p.push_str(suffix);
     PathBuf::from(p)
 }
 
-pub fn numbered_backup_path(path: &Path) -> PathBuf {
+fn numbered_backup_path(path: &Path) -> PathBuf {
     for i in 1_u64.. {
         let path_str = &format!("{}.~{}~", path.to_string_lossy(), i);
         let path = Path::new(path_str);
@@ -99,7 +237,7 @@ pub fn numbered_backup_path(path: &Path) -> PathBuf {
     panic!("cannot create backup")
 }
 
-pub fn existing_backup_path(path: &Path, suffix: &str) -> PathBuf {
+fn existing_backup_path(path: &Path, suffix: &str) -> PathBuf {
     let test_path_str = &format!("{}.~1~", path.to_string_lossy());
     let test_path = Path::new(test_path_str);
     if test_path.exists() {
@@ -108,3 +246,210 @@ pub fn existing_backup_path(path: &Path, suffix: &str) -> PathBuf {
         simple_backup_path(path, suffix)
     }
 }
+
+//
+// Tests for this module
+//
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::env;
+    // Required to instantiate mutex in shared context
+    use lazy_static::lazy_static;
+    use std::sync::Mutex;
+
+    // The mutex is required here as by default all tests are run as separate
+    // threads under the same parent process. As environment variables are
+    // specific to processes (and thus shared among threads), data races *will*
+    // occur if no precautions are taken. Thus we have all tests that rely on
+    // environment variables lock this empty mutex to ensure they don't access
+    // it concurrently.
+    lazy_static! {
+        static ref TEST_MUTEX: Mutex<()> = Mutex::new(());
+    }
+
+    // Environment variable for "VERSION_CONTROL"
+    static ENV_VERSION_CONTROL: &str = "VERSION_CONTROL";
+
+    // Defaults to --backup=existing
+    #[test]
+    fn test_backup_mode_short_only() {
+        let short_opt_present = true;
+        let long_opt_present = false;
+        let long_opt_value = None;
+        let _dummy = TEST_MUTEX.lock().unwrap();
+
+        let result =
+            determine_backup_mode(short_opt_present, long_opt_present, long_opt_value).unwrap();
+
+        assert_eq!(result, BackupMode::ExistingBackup);
+    }
+
+    // --backup takes precedence over -b
+    #[test]
+    fn test_backup_mode_long_preferred_over_short() {
+        let short_opt_present = true;
+        let long_opt_present = true;
+        let long_opt_value = Some("none");
+        let _dummy = TEST_MUTEX.lock().unwrap();
+
+        let result =
+            determine_backup_mode(short_opt_present, long_opt_present, long_opt_value).unwrap();
+
+        assert_eq!(result, BackupMode::NoBackup);
+    }
+
+    // --backup can be passed without an argument
+    #[test]
+    fn test_backup_mode_long_without_args_no_env() {
+        let short_opt_present = false;
+        let long_opt_present = true;
+        let long_opt_value = None;
+        let _dummy = TEST_MUTEX.lock().unwrap();
+
+        let result =
+            determine_backup_mode(short_opt_present, long_opt_present, long_opt_value).unwrap();
+
+        assert_eq!(result, BackupMode::ExistingBackup);
+    }
+
+    // --backup can be passed with an argument only
+    #[test]
+    fn test_backup_mode_long_with_args() {
+        let short_opt_present = false;
+        let long_opt_present = true;
+        let long_opt_value = Some("simple");
+        let _dummy = TEST_MUTEX.lock().unwrap();
+
+        let result =
+            determine_backup_mode(short_opt_present, long_opt_present, long_opt_value).unwrap();
+
+        assert_eq!(result, BackupMode::SimpleBackup);
+    }
+
+    // --backup errors on invalid argument
+    #[test]
+    fn test_backup_mode_long_with_args_invalid() {
+        let short_opt_present = false;
+        let long_opt_present = true;
+        let long_opt_value = Some("foobar");
+        let _dummy = TEST_MUTEX.lock().unwrap();
+
+        let result = determine_backup_mode(short_opt_present, long_opt_present, long_opt_value);
+
+        assert!(result.is_err());
+        let text = result.unwrap_err();
+        assert!(text.contains("invalid argument ‘foobar’ for ‘backup type’"));
+    }
+
+    // --backup errors on ambiguous argument
+    #[test]
+    fn test_backup_mode_long_with_args_ambiguous() {
+        let short_opt_present = false;
+        let long_opt_present = true;
+        let long_opt_value = Some("n");
+        let _dummy = TEST_MUTEX.lock().unwrap();
+
+        let result = determine_backup_mode(short_opt_present, long_opt_present, long_opt_value);
+
+        assert!(result.is_err());
+        let text = result.unwrap_err();
+        assert!(text.contains("ambiguous argument ‘n’ for ‘backup type’"));
+    }
+
+    // --backup accepts shortened arguments (si for simple)
+    #[test]
+    fn test_backup_mode_long_with_arg_shortened() {
+        let short_opt_present = false;
+        let long_opt_present = true;
+        let long_opt_value = Some("si");
+        let _dummy = TEST_MUTEX.lock().unwrap();
+
+        let result =
+            determine_backup_mode(short_opt_present, long_opt_present, long_opt_value).unwrap();
+
+        assert_eq!(result, BackupMode::SimpleBackup);
+    }
+
+    // -b ignores the "VERSION_CONTROL" environment variable
+    #[test]
+    fn test_backup_mode_short_only_ignore_env() {
+        let short_opt_present = true;
+        let long_opt_present = false;
+        let long_opt_value = None;
+        let _dummy = TEST_MUTEX.lock().unwrap();
+        env::set_var(ENV_VERSION_CONTROL, "none");
+
+        let result =
+            determine_backup_mode(short_opt_present, long_opt_present, long_opt_value).unwrap();
+
+        assert_eq!(result, BackupMode::ExistingBackup);
+        env::remove_var(ENV_VERSION_CONTROL);
+    }
+
+    // --backup can be passed without an argument, but reads env var if existent
+    #[test]
+    fn test_backup_mode_long_without_args_with_env() {
+        let short_opt_present = false;
+        let long_opt_present = true;
+        let long_opt_value = None;
+        let _dummy = TEST_MUTEX.lock().unwrap();
+        env::set_var(ENV_VERSION_CONTROL, "none");
+
+        let result =
+            determine_backup_mode(short_opt_present, long_opt_present, long_opt_value).unwrap();
+
+        assert_eq!(result, BackupMode::NoBackup);
+        env::remove_var(ENV_VERSION_CONTROL);
+    }
+
+    // --backup errors on invalid VERSION_CONTROL env var
+    #[test]
+    fn test_backup_mode_long_with_env_var_invalid() {
+        let short_opt_present = false;
+        let long_opt_present = true;
+        let long_opt_value = None;
+        let _dummy = TEST_MUTEX.lock().unwrap();
+        env::set_var(ENV_VERSION_CONTROL, "foobar");
+
+        let result = determine_backup_mode(short_opt_present, long_opt_present, long_opt_value);
+
+        assert!(result.is_err());
+        let text = result.unwrap_err();
+        assert!(text.contains("invalid argument ‘foobar’ for ‘$VERSION_CONTROL’"));
+        env::remove_var(ENV_VERSION_CONTROL);
+    }
+
+    // --backup errors on ambiguous VERSION_CONTROL env var
+    #[test]
+    fn test_backup_mode_long_with_env_var_ambiguous() {
+        let short_opt_present = false;
+        let long_opt_present = true;
+        let long_opt_value = None;
+        let _dummy = TEST_MUTEX.lock().unwrap();
+        env::set_var(ENV_VERSION_CONTROL, "n");
+
+        let result = determine_backup_mode(short_opt_present, long_opt_present, long_opt_value);
+
+        assert!(result.is_err());
+        let text = result.unwrap_err();
+        assert!(text.contains("ambiguous argument ‘n’ for ‘$VERSION_CONTROL’"));
+        env::remove_var(ENV_VERSION_CONTROL);
+    }
+
+    // --backup accepts shortened env vars (si for simple)
+    #[test]
+    fn test_backup_mode_long_with_env_var_shortened() {
+        let short_opt_present = false;
+        let long_opt_present = true;
+        let long_opt_value = None;
+        let _dummy = TEST_MUTEX.lock().unwrap();
+        env::set_var(ENV_VERSION_CONTROL, "si");
+
+        let result =
+            determine_backup_mode(short_opt_present, long_opt_present, long_opt_value).unwrap();
+
+        assert_eq!(result, BackupMode::SimpleBackup);
+        env::remove_var(ENV_VERSION_CONTROL);
+    }
+}
diff --git a/src/uucore/src/lib/mods/error.rs b/src/uucore/src/lib/mods/error.rs
index ae509ff00..d82da9feb 100644
--- a/src/uucore/src/lib/mods/error.rs
+++ b/src/uucore/src/lib/mods/error.rs
@@ -138,6 +138,12 @@ pub enum UError {
 }
 
 impl UError {
+    /// The error code of [`UResult`]
+    ///
+    /// This function defines the error code associated with an instance of
+    /// [`UResult`]. To associate error codes for self-defined instances of
+    /// `UResult::Custom` (i.e. [`UCustomError`]), implement the
+    /// [`code`-function there](UCustomError::code).
     pub fn code(&self) -> i32 {
         match self {
             UError::Common(e) => e.code(),
@@ -145,6 +151,13 @@ impl UError {
         }
     }
 
+    /// Whether to print usage help for a [`UResult`]
+    ///
+    /// Defines if a variant of [`UResult`] should print a short usage message
+    /// below the error. The usage message is printed when this function returns
+    /// `true`. To do this for self-defined instances of `UResult::Custom` (i.e.
+    /// [`UCustomError`]), implement the [`usage`-function
+    /// there](UCustomError::usage).
     pub fn usage(&self) -> bool {
         match self {
             UError::Common(e) => e.usage(),
@@ -183,12 +196,13 @@ impl Display for UError {
 /// Custom errors defined by the utils.
 ///
 /// All errors should implement [`std::error::Error`], [`std::fmt::Display`] and
-/// [`std::fmt::Debug`] and have an additional `code` method that specifies the exit code of the
-/// program if the error is returned from `uumain`.
+/// [`std::fmt::Debug`] and have an additional `code` method that specifies the
+/// exit code of the program if the error is returned from `uumain`.
 ///
 /// An example of a custom error from `ls`:
+///
 /// ```
-/// use uucore::error::{UCustomError};
+/// use uucore::error::{UCustomError, UResult};
 /// use std::{
 ///     error::Error,
 ///     fmt::{Display, Debug},
@@ -221,13 +235,121 @@ impl Display for UError {
 ///     }
 /// }
 /// ```
-/// A crate like [`quick_error`](https://crates.io/crates/quick-error) might also be used, but will
-/// still require an `impl` for the `code` method.
-pub trait UCustomError: Error {
+///
+/// The main routine would look like this:
+///
+/// ```ignore
+/// #[uucore_procs::gen_uumain]
+/// pub fn uumain(args: impl uucore::Args) -> UResult<()> {
+///     // Perform computations here ...
+///     return Err(LsError::InvalidLineWidth(String::from("test")).into())
+/// }
+/// ```
+///
+/// The call to `into()` is required to convert the [`UCustomError`] to an
+/// instance of [`UError`].
+///
+/// A crate like [`quick_error`](https://crates.io/crates/quick-error) might
+/// also be used, but will still require an `impl` for the `code` method.
+pub trait UCustomError: Error + Send {
+    /// Error code of a custom error.
+    ///
+    /// Set a return value for each variant of an enum-type to associate an
+    /// error code (which is returned to the system shell) with an error
+    /// variant.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use uucore::error::{UCustomError};
+    /// use std::{
+    ///     error::Error,
+    ///     fmt::{Display, Debug},
+    ///     path::PathBuf
+    /// };
+    ///
+    /// #[derive(Debug)]
+    /// enum MyError {
+    ///     Foo(String),
+    ///     Bar(PathBuf),
+    ///     Bing(),
+    /// }
+    ///
+    /// impl UCustomError for MyError {
+    ///     fn code(&self) -> i32 {
+    ///         match self {
+    ///             MyError::Foo(_) => 2,
+    ///             // All other errors yield the same error code, there's no
+    ///             // need to list them explicitly.
+    ///             _ => 1,
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// impl Error for MyError {}
+    ///
+    /// impl Display for MyError {
+    ///     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    ///         use MyError as ME;
+    ///         match self {
+    ///             ME::Foo(s) => write!(f, "Unknown Foo: '{}'", s),
+    ///             ME::Bar(p) => write!(f, "Couldn't find Bar: '{}'", p.display()),
+    ///             ME::Bing() => write!(f, "Exterminate!"),
+    ///         }
+    ///     }
+    /// }
+    /// ```
     fn code(&self) -> i32 {
         1
     }
 
+    /// Print usage help to a custom error.
+    ///
+    /// Return true or false to control whether a short usage help is printed
+    /// below the error message. The usage help is in the format: "Try '{name}
+    /// --help' for more information." and printed only if `true` is returned.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use uucore::error::{UCustomError};
+    /// use std::{
+    ///     error::Error,
+    ///     fmt::{Display, Debug},
+    ///     path::PathBuf
+    /// };
+    ///
+    /// #[derive(Debug)]
+    /// enum MyError {
+    ///     Foo(String),
+    ///     Bar(PathBuf),
+    ///     Bing(),
+    /// }
+    ///
+    /// impl UCustomError for MyError {
+    ///     fn usage(&self) -> bool {
+    ///         match self {
+    ///             // This will have a short usage help appended
+    ///             MyError::Bar(_) => true,
+    ///             // These matches won't have a short usage help appended
+    ///             _ => false,
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// impl Error for MyError {}
+    ///
+    /// impl Display for MyError {
+    ///     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    ///         use MyError as ME;
+    ///         match self {
+    ///             ME::Foo(s) => write!(f, "Unknown Foo: '{}'", s),
+    ///             ME::Bar(p) => write!(f, "Couldn't find Bar: '{}'", p.display()),
+    ///             ME::Bing() => write!(f, "Exterminate!"),
+    ///         }
+    ///     }
+    /// }
+    /// ```
     fn usage(&self) -> bool {
         false
     }
diff --git a/tests/by-util/test_du.rs b/tests/by-util/test_du.rs
index 607d5dc45..efc097773 100644
--- a/tests/by-util/test_du.rs
+++ b/tests/by-util/test_du.rs
@@ -398,8 +398,7 @@ fn test_du_time() {
     let result = ts.ucmd().arg("--time=ctime").arg("date_test").succeeds();
     result.stdout_only("0\t2016-06-16 00:00\tdate_test\n");
 
-    #[cfg(not(target_env = "musl"))]
-    {
+    if birth_supported() {
         use regex::Regex;
 
         let re_birth =
@@ -409,6 +408,16 @@ fn test_du_time() {
     }
 }
 
+#[cfg(feature = "touch")]
+fn birth_supported() -> bool {
+    let ts = TestScenario::new(util_name!());
+    let m = match std::fs::metadata(ts.fixtures.subdir) {
+        Ok(m) => m,
+        Err(e) => panic!("{}", e),
+    };
+    m.created().is_ok()
+}
+
 #[cfg(not(target_os = "windows"))]
 #[cfg(feature = "chmod")]
 #[test]
diff --git a/tests/by-util/test_expand.rs b/tests/by-util/test_expand.rs
index 834a09736..9c06fe904 100644
--- a/tests/by-util/test_expand.rs
+++ b/tests/by-util/test_expand.rs
@@ -1,4 +1,5 @@
 use crate::common::util::*;
+// spell-checker:ignore (ToDO) taaaa tbbbb tcccc
 
 #[test]
 fn test_with_tab() {
@@ -53,3 +54,140 @@ fn test_with_multiple_files() {
         .stdout_contains("    return")
         .stdout_contains("        ");
 }
+
+#[test]
+fn test_tabs_space_separated_list() {
+    new_ucmd!()
+        .args(&["--tabs", "3 6 9"])
+        .pipe_in("a\tb\tc\td\te")
+        .succeeds()
+        .stdout_is("a  b  c  d e");
+}
+
+#[test]
+fn test_tabs_mixed_style_list() {
+    new_ucmd!()
+        .args(&["--tabs", ", 3,6 9"])
+        .pipe_in("a\tb\tc\td\te")
+        .succeeds()
+        .stdout_is("a  b  c  d e");
+}
+
+#[test]
+fn test_tabs_empty_string() {
+    new_ucmd!()
+        .args(&["--tabs", ""])
+        .pipe_in("a\tb\tc")
+        .succeeds()
+        .stdout_is("a       b       c");
+}
+
+#[test]
+fn test_tabs_comma_only() {
+    new_ucmd!()
+        .args(&["--tabs", ","])
+        .pipe_in("a\tb\tc")
+        .succeeds()
+        .stdout_is("a       b       c");
+}
+
+#[test]
+fn test_tabs_space_only() {
+    new_ucmd!()
+        .args(&["--tabs", " "])
+        .pipe_in("a\tb\tc")
+        .succeeds()
+        .stdout_is("a       b       c");
+}
+
+#[test]
+fn test_tabs_slash() {
+    new_ucmd!()
+        .args(&["--tabs", "/"])
+        .pipe_in("a\tb\tc")
+        .succeeds()
+        .stdout_is("a       b       c");
+}
+
+#[test]
+fn test_tabs_plus() {
+    new_ucmd!()
+        .args(&["--tabs", "+"])
+        .pipe_in("a\tb\tc")
+        .succeeds()
+        .stdout_is("a       b       c");
+}
+
+#[test]
+fn test_tabs_trailing_slash() {
+    new_ucmd!()
+        .arg("--tabs=1,/5")
+        .pipe_in("\ta\tb\tc")
+        .succeeds()
+        //          0         1
+        //          01234567890
+        .stdout_is(" a   b    c");
+}
+
+#[test]
+fn test_tabs_trailing_slash_long_columns() {
+    new_ucmd!()
+        .arg("--tabs=1,/3")
+        .pipe_in("\taaaa\tbbbb\tcccc")
+        .succeeds()
+        //          0         1
+        //          01234567890123456
+        .stdout_is(" aaaa bbbb  cccc");
+}
+
+#[test]
+fn test_tabs_trailing_plus() {
+    new_ucmd!()
+        .arg("--tabs=1,+5")
+        .pipe_in("\ta\tb\tc")
+        .succeeds()
+        //          0         1
+        //          012345678901
+        .stdout_is(" a    b    c");
+}
+
+#[test]
+fn test_tabs_trailing_plus_long_columns() {
+    new_ucmd!()
+        .arg("--tabs=1,+3")
+        .pipe_in("\taaaa\tbbbb\tcccc")
+        .succeeds()
+        //          0         1
+        //          012345678901234567
+        .stdout_is(" aaaa  bbbb  cccc");
+}
+
+#[test]
+fn test_tabs_must_be_ascending() {
+    new_ucmd!()
+        .arg("--tabs=1,1")
+        .fails()
+        .stderr_contains("tab sizes must be ascending");
+}
+
+#[test]
+fn test_tabs_keep_last_trailing_specifier() {
+    // If there are multiple trailing specifiers, use only the last one
+    // before the number.
+    new_ucmd!()
+        .arg("--tabs=1,+/+/5")
+        .pipe_in("\ta\tb\tc")
+        .succeeds()
+        //          0         1
+        //          01234567890
+        .stdout_is(" a   b    c");
+}
+
+#[test]
+fn test_tabs_comma_separated_no_numbers() {
+    new_ucmd!()
+        .arg("--tabs=+,/,+,/")
+        .pipe_in("\ta\tb\tc")
+        .succeeds()
+        .stdout_is("        a       b       c");
+}
diff --git a/tests/by-util/test_sleep.rs b/tests/by-util/test_sleep.rs
index a17beddf6..94a0a6896 100644
--- a/tests/by-util/test_sleep.rs
+++ b/tests/by-util/test_sleep.rs
@@ -110,3 +110,8 @@ fn test_sleep_sum_duration_many() {
     let duration = before_test.elapsed();
     assert!(duration >= millis_900);
 }
+
+#[test]
+fn test_sleep_wrong_time() {
+    new_ucmd!().args(&["0.1s", "abc"]).fails();
+}
diff --git a/tests/by-util/test_sort.rs b/tests/by-util/test_sort.rs
index 4a1cc3fa9..1f21722ed 100644
--- a/tests/by-util/test_sort.rs
+++ b/tests/by-util/test_sort.rs
@@ -181,7 +181,7 @@ fn test_check_zero_terminated_failure() {
         .arg("-c")
         .arg("zero-terminated.txt")
         .fails()
-        .stdout_is("sort: zero-terminated.txt:2: disorder: ../../fixtures/du\n");
+        .stderr_only("sort: zero-terminated.txt:2: disorder: ../../fixtures/du\n");
 }
 
 #[test]
@@ -220,32 +220,29 @@ fn test_random_shuffle_contains_all_lines() {
 
 #[test]
 fn test_random_shuffle_two_runs_not_the_same() {
-    // check to verify that two random shuffles are not equal; this has the
-    // potential to fail in the very unlikely event that the random order is the same
-    // as the starting order, or if both random sorts end up having the same order.
-    const FILE: &str = "default_unsorted_ints.expected";
-    let (at, _ucmd) = at_and_ucmd!();
-    let result = new_ucmd!().arg("-R").arg(FILE).run().stdout_move_str();
-    let expected = at.read(FILE);
-    let unexpected = new_ucmd!().arg("-R").arg(FILE).run().stdout_move_str();
+    for arg in &["-R", "-k1,1R"] {
+        // check to verify that two random shuffles are not equal; this has the
+        // potential to fail in the very unlikely event that the random order is the same
+        // as the starting order, or if both random sorts end up having the same order.
+        const FILE: &str = "default_unsorted_ints.expected";
+        let (at, _ucmd) = at_and_ucmd!();
+        let result = new_ucmd!().arg(arg).arg(FILE).run().stdout_move_str();
+        let expected = at.read(FILE);
+        let unexpected = new_ucmd!().arg(arg).arg(FILE).run().stdout_move_str();
 
-    assert_ne!(result, expected);
-    assert_ne!(result, unexpected);
+        assert_ne!(result, expected);
+        assert_ne!(result, unexpected);
+    }
 }
 
 #[test]
-fn test_random_shuffle_contains_two_runs_not_the_same() {
-    // check to verify that two random shuffles are not equal; this has the
-    // potential to fail in the unlikely event that random order is the same
-    // as the starting order, or if both random sorts end up having the same order.
-    const FILE: &str = "default_unsorted_ints.expected";
-    let (at, _ucmd) = at_and_ucmd!();
-    let result = new_ucmd!().arg("-R").arg(FILE).run().stdout_move_str();
-    let expected = at.read(FILE);
-    let unexpected = new_ucmd!().arg("-R").arg(FILE).run().stdout_move_str();
-
-    assert_ne!(result, expected);
-    assert_ne!(result, unexpected);
+fn test_random_ignore_case() {
+    let input = "ABC\nABc\nAbC\nAbc\naBC\naBc\nabC\nabc\n";
+    new_ucmd!()
+        .args(&["-fR"])
+        .pipe_in(input)
+        .succeeds()
+        .stdout_is(input);
 }
 
 #[test]
@@ -774,14 +771,15 @@ fn test_check() {
         new_ucmd!()
             .arg(diagnose_arg)
             .arg("check_fail.txt")
+            .arg("--buffer-size=10b")
             .fails()
-            .stdout_is("sort: check_fail.txt:6: disorder: 5\n");
+            .stderr_only("sort: check_fail.txt:6: disorder: 5\n");
 
         new_ucmd!()
             .arg(diagnose_arg)
             .arg("multiple_files.expected")
             .succeeds()
-            .stdout_is("");
+            .stderr_is("");
     }
 }
 
@@ -796,6 +794,18 @@ fn test_check_silent() {
     }
 }
 
+#[test]
+fn test_check_unique() {
+    // Due to a clap bug the combination "-cu" does not work. "-c -u" works.
+    // See https://github.com/clap-rs/clap/issues/2624
+    new_ucmd!()
+        .args(&["-c", "-u"])
+        .pipe_in("A\nA\n")
+        .fails()
+        .code_is(1)
+        .stderr_only("sort: -:2: disorder: A");
+}
+
 #[test]
 fn test_dictionary_and_nonprinting_conflicts() {
     let conflicting_args = ["n", "h", "g", "M"];
@@ -839,9 +849,9 @@ fn test_nonexistent_file() {
         .status_code(2)
         .stderr_only(
             #[cfg(not(windows))]
-            "sort: cannot read: \"nonexistent.txt\": No such file or directory (os error 2)",
+            "sort: cannot read: nonexistent.txt: No such file or directory",
             #[cfg(windows)]
-            "sort: cannot read: \"nonexistent.txt\": The system cannot find the file specified. (os error 2)",
+            "sort: cannot read: nonexistent.txt: The system cannot find the file specified.",
         );
 }
 
@@ -883,6 +893,29 @@ fn test_compress() {
         .stdout_only_fixture("ext_sort.expected");
 }
 
+#[test]
+#[cfg(target_os = "linux")]
+fn test_compress_merge() {
+    new_ucmd!()
+        .args(&[
+            "--compress-program",
+            "gzip",
+            "-S",
+            "10",
+            "--batch-size=2",
+            "-m",
+            "--unique",
+            "merge_ints_interleaved_1.txt",
+            "merge_ints_interleaved_2.txt",
+            "merge_ints_interleaved_3.txt",
+            "merge_ints_interleaved_3.txt",
+            "merge_ints_interleaved_2.txt",
+            "merge_ints_interleaved_1.txt",
+        ])
+        .succeeds()
+        .stdout_only_fixture("merge_ints_interleaved.expected");
+}
+
 #[test]
 fn test_compress_fail() {
     TestScenario::new(util_name!())
@@ -959,3 +992,102 @@ fn test_key_takes_one_arg() {
         .succeeds()
         .stdout_is_fixture("keys_open_ended.expected");
 }
+
+#[test]
+fn test_verifies_out_file() {
+    let inputs = ["" /* no input */, "some input"];
+    for &input in &inputs {
+        new_ucmd!()
+            .args(&["-o", "nonexistent_dir/nonexistent_file"])
+            .pipe_in(input)
+            .ignore_stdin_write_error()
+            .fails()
+            .status_code(2)
+            .stderr_only(
+                #[cfg(not(windows))]
+                "sort: open failed: nonexistent_dir/nonexistent_file: No such file or directory",
+                #[cfg(windows)]
+                "sort: open failed: nonexistent_dir/nonexistent_file: The system cannot find the path specified.",
+            );
+    }
+}
+
+#[test]
+fn test_verifies_files_after_keys() {
+    new_ucmd!()
+        .args(&[
+            "-o",
+            "nonexistent_dir/nonexistent_file",
+            "-k",
+            "0",
+            "nonexistent_dir/input_file",
+        ])
+        .fails()
+        .status_code(2)
+        .stderr_contains("failed to parse key");
+}
+
+#[test]
+#[cfg(unix)]
+fn test_verifies_input_files() {
+    new_ucmd!()
+        .args(&["/dev/random", "nonexistent_file"])
+        .fails()
+        .status_code(2)
+        .stderr_is("sort: cannot read: nonexistent_file: No such file or directory");
+}
+
+#[test]
+fn test_separator_null() {
+    new_ucmd!()
+        .args(&["-k1,1", "-k3,3", "-t", "\\0"])
+        .pipe_in("z\0a\0b\nz\0b\0a\na\0z\0z\n")
+        .succeeds()
+        .stdout_only("a\0z\0z\nz\0b\0a\nz\0a\0b\n");
+}
+
+#[test]
+fn test_output_is_input() {
+    let input = "a\nb\nc\n";
+    let (at, mut cmd) = at_and_ucmd!();
+    at.touch("file");
+    at.append("file", input);
+    cmd.args(&["-m", "-u", "-o", "file", "file", "file", "file"])
+        .succeeds();
+    assert_eq!(at.read("file"), input);
+}
+
+#[test]
+#[cfg(unix)]
+fn test_output_device() {
+    new_ucmd!()
+        .args(&["-o", "/dev/null"])
+        .pipe_in("input")
+        .succeeds();
+}
+
+#[test]
+fn test_merge_empty_input() {
+    new_ucmd!()
+        .args(&["-m", "empty.txt"])
+        .succeeds()
+        .no_stderr()
+        .no_stdout();
+}
+
+#[test]
+fn test_no_error_for_version() {
+    new_ucmd!()
+        .arg("--version")
+        .succeeds()
+        .stdout_contains("sort");
+}
+
+#[test]
+fn test_wrong_args_exit_code() {
+    new_ucmd!()
+        .arg("--misspelled")
+        .fails()
+        .status_code(2)
+        .stderr_contains("--misspelled");
+}
diff --git a/tests/by-util/test_stat.rs b/tests/by-util/test_stat.rs
index 7cff0d89c..af9e3de45 100644
--- a/tests/by-util/test_stat.rs
+++ b/tests/by-util/test_stat.rs
@@ -64,7 +64,7 @@ mod test_generate_tokens {
 
     #[test]
     fn printf_format() {
-        let s = "%-# 15a\\r\\\"\\\\\\a\\b\\e\\f\\v%+020.-23w\\x12\\167\\132\\112\\n";
+        let s = "%-# 15a\\t\\r\\\"\\\\\\a\\b\\e\\f\\v%+020.-23w\\x12\\167\\132\\112\\n";
         let expected = vec![
             Token::Directive {
                 flag: F_LEFT | F_ALTER | F_SPACE,
@@ -72,6 +72,7 @@ mod test_generate_tokens {
                 precision: -1,
                 format: 'a',
             },
+            Token::Char('\t'),
             Token::Char('\r'),
             Token::Char('"'),
             Token::Char('\\'),
diff --git a/tests/by-util/test_tac.rs b/tests/by-util/test_tac.rs
index a8adbb28e..5fc88770f 100644
--- a/tests/by-util/test_tac.rs
+++ b/tests/by-util/test_tac.rs
@@ -66,5 +66,10 @@ fn test_invalid_input() {
         .ucmd()
         .arg("a")
         .fails()
-        .stderr_contains("dir: read error: Invalid argument");
+        .stderr_contains("a: read error: Invalid argument");
+}
+
+#[test]
+fn test_no_line_separators() {
+    new_ucmd!().pipe_in("a").succeeds().stdout_is("a");
 }
diff --git a/tests/by-util/test_tail.rs b/tests/by-util/test_tail.rs
index e8dd63317..28c3580bb 100644
--- a/tests/by-util/test_tail.rs
+++ b/tests/by-util/test_tail.rs
@@ -23,6 +23,15 @@ fn test_stdin_default() {
         .stdout_is_fixture("foobar_stdin_default.expected");
 }
 
+#[test]
+fn test_stdin_explicit() {
+    new_ucmd!()
+        .pipe_in_fixture(FOOBAR_TXT)
+        .arg("-")
+        .run()
+        .stdout_is_fixture("foobar_stdin_default.expected");
+}
+
 #[test]
 fn test_single_default() {
     new_ucmd!()
diff --git a/tests/fixtures/sort/empty.txt b/tests/fixtures/sort/empty.txt
new file mode 100644
index 000000000..e69de29bb