echo: Support octal, hexadecimal and unicode escape sequences

Base/usr/share/man/man1/echo.md

@@ -5,21 +5,51 @@ echo - print the given text
 ## Synopsis
 
 ```**sh
-$ echo [-n] text...
+$ echo [-ne] [text...]
 ```
 
 ## Description
 
-Print the given *text*, which is passed as argv, to the standard output,
-separating arguments with a space character.
+Print the given `text` to the standard output. If multiple `text`s are provided, they will be joined with a space character. If no `text` is provided, an empty line will be printed.
+
+Character escape sequences and their meanings are as follows:
+
+`\\a` - `<alert>`
+
+`\\b` - `<backspace>`
+
+`\\c` - Suppress the output of all remaining characters, including the trailing newline.
+
+`\\e` - The escape character (`\\033`).
+
+`\\f` - `<form-feed>`
+
+`\\n` - `<newline>`
+
+`\\r` - `<carriage-return>`
+
+`\\t` - `<tab>`
+
+`\\v` - `<vertical-tab>`
+
+`\\\\` - The backslash character (`\\`).
+
+`\\0ooo` - A byte whose value is a zero, one, two, or three-digit octal number.
+
+`\\xHH` - A byte whose value is a two-digit hexadecimal number.
+
+`\\uHHHH` - An unicode code point whose value is a four-digit hexadecimal number.
 
 ## Options
 
 * `-n`: Do not output a trailing newline
+* `-e`: Interpret backslash escapes
 
 ## Examples
 
 ```sh
 $ echo hello friends!
 hello friends!
+$ echo -ne '\x68\x65\x6c\x6c\x6f' 'friends\041\n'
+hello friends!
 ```