AK/Userland: Add single value to ArgsParser usage, and port tail to use ArgsParser

AK/ArgsParser.cpp

@@ -112,6 +112,12 @@ bool ArgsParser::check_required_args(const ArgsParserResult& res)
                 return false;
         }
     }
+
+    if (m_single_value_required) {
+        if (res.m_single_values.size() == 0)
+            return false;
+    }
+
     return true;
 }
 
@@ -135,6 +141,18 @@ void ArgsParser::add_arg(const String& name, const String& value_name, const Str
     m_args.set(name, Arg(name, value_name, description, false));
 }
 
+void ArgsParser::set_single_value(const String& name)
+{
+    m_single_value_name = name;
+    m_single_value_required = false;
+}
+
+void ArgsParser::set_required_single_value(const String& name)
+{
+    m_single_value_name = name;
+    m_single_value_required = true;
+}
+
 String ArgsParser::get_usage() const
 {
     StringBuilder sb;
@@ -163,6 +181,20 @@ String ArgsParser::get_usage() const
             sb.append("] ");
     }
 
+    if (m_single_value_name.length()) {
+        if (m_single_value_required)
+            sb.append("<");
+        else
+            sb.append("[");
+
+        sb.append(m_single_value_name);
+
+        if (m_single_value_required)
+            sb.append(">");
+        else
+            sb.append("]");
+    }
+
     sb.append("\n");
 
     for (auto& it : m_args) {

AK/ArgsParser.h

@@ -38,6 +38,8 @@ public:
     void add_required_arg(const String& name, const String& value_name, const String& description);
     void add_arg(const String& name, const String& description);
     void add_arg(const String& name, const String& value_name, const String& description);
+    void set_single_value(const String& name);
+    void set_required_single_value(const String& name);
     String get_usage() const;
     void print_usage() const;
 
@@ -59,6 +61,8 @@ private:
 
     String m_program_name;
     String m_prefix;
+    String m_single_value_name;
+    bool m_single_value_required = false;
     HashMap<String, Arg> m_args;
 };
 

Userland/tail.cpp

@@ -2,17 +2,11 @@
 #include <string.h>
 #include <stdlib.h>
 #include <errno.h>
-#include <getopt.h>
 #include <unistd.h>
 #include <AK/Assertions.h>
+#include <AK/ArgsParser.h>
 #include <LibCore/CFile.h>
 
-static void print_usage_and_exit()
-{
-    printf("usage: tail [-f, -n <linecount>] <filename>\n");
-    exit(1);
-}
-
 int tail_from_pos(CFile& file, off_t startline, bool want_follow)
 {
     if (!file.seek(startline + 1))
@@ -81,37 +75,38 @@ static void exit_because_we_wanted_lines()
 
 int main(int argc, char *argv[])
 {
+    AK::ArgsParser args_parser("tail");
+
+    args_parser.add_arg("f", "follow -- appended data is output as it is written to the file");
+    args_parser.add_arg("n", "lines", "fetch the specified number of lines");
+    args_parser.set_required_single_value("file");
+
+    AK::ArgsParserResult args = args_parser.parse(argc, (const char**)argv);
+
+    Vector<String> values = args.get_single_values();
+    if (values.size() != 1) {
+        args_parser.print_usage();
+        return -1;
+    }
+
     int line_count = 0;
-    bool flag_follow = false;
-    int opt;
-    while ((opt = getopt(argc, argv, "fn:")) != -1) {
-        switch (opt) {
-        case 'f':
-            flag_follow = true;
-            break;
-        case 'n':
-            line_count = strtol(optarg, NULL, 10);
-            if (errno == EINVAL) {
-                exit_because_we_wanted_lines();
-            }
-            break;
-        default:
-            print_usage_and_exit();
+    if (args.is_present("n")) {
+        line_count = strtol(args.get("n").characters(), NULL, 10);
+        if (errno == EINVAL) {
+            args_parser.print_usage();
+            return -1;
         }
     }
-    const char *path = nullptr;
-    if (optind >= argc) {
-        print_usage_and_exit();
-    }
 
-    path = argv[optind];
-
-    CFile f(path);
+    CFile f(values[0]);
     if (!f.open(CIODevice::ReadOnly)) {
-        fprintf(stderr, "Error opening file %s: %s\n", path, strerror(errno));
+        fprintf(stderr, "Error opening file %s: %s\n", f.filename().characters(), strerror(errno));
         exit(-1);
     }
 
+    bool flag_follow = args.is_present("f");
+    bool o_arg = args.is_present("o");
+
     auto pos = find_seek_pos(f, line_count);
     return tail_from_pos(f, pos, flag_follow);
 }