Base: Add manpage for xargs

Author: https://github.com/alimpfard
Commit: https://github.com/SerenityOS/serenity/commit/ca6e3612792
Pull-request: https://github.com/SerenityOS/serenity/pull/2416
Reviewed-by: https://github.com/bugaevc

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

@@ -0,0 +1,47 @@
+## Name
+
+xargs - build and execute commandlines from input
+
+## Synopsis
+
+```**sh
+$ xargs [options...] [command [initial-arguments...]]
+```
+
+## Description
+
+`xargs` reads items from a stream, delimited by some blank character (`delimiter`), and executes the `command` as many times as there are items, with any processed `initial-arguments`, possibly followed by a number of items read from the input.
+
+If a `placeholder` is explicitly specified, the `max-lines` limit is set to 1, and each argument in `initial-arguments` is processed by replacing any occurence of the `placeholder` with the input item, and treating the entire resulting value as _one_ argument.
+
+It is to be noted that `command` is also subject to substitution in this mode.
+
+If no argument in `command` or `initial-arguments` contains the `placeholder`, an argument is added at the end of the list containing only the `placeholder`.
+
+
+If a `placeholder` is not explicitly specified, no substitution will be performed, rather, the item(s) will be appended to the end of the command line, until either of the following conditions are met:
+- Adding another argument would overflow the system maximum command length (or the provided `max-chars` limit)
+- The number of lines used per command (`max-lines`) would be exceeded
+
+
+`xargs` will read the items from standard input by default, and when data is read from standard input, the standard input of `command` is redirected to read from `/dev/null`.
+The standard input is left as-is if data is read from a file.
+
+## Options
+
+* `-I`, `--replace`: Set the `placeholder`, and force `max-lines` to 1
+* `-0`, `--null`: Split the items by zero bytes (null characters) instead of `delimiter`
+* `-d`, `--delimiter`: Set the `delimiter`, which is a newline (`\n`) by default
+* `-v`, `--verbose`: Display each expanded command on standard error before executing it
+* `-a`, `--arg-file`: Read the items from the speified file, `-` refers to standard input and is the default
+* `-L`, `--line-limit`: Set `max-lines`, `0` means unlimited (which is the default)
+* `-s`, `--char-limit`: Set `max-chars`, which is `ARG_MAX` (the maximum command size supported by the system) by default
+
+## Examples
+
+```sh
+$ pro http://list-of-example-urls.com/plain | xargs -I 'URL' pro URL > concatenated-outputs
+$ xargs -a list-of-files-to-delete --verbose rm
+$ xargs -a list-of-moves -L 2 mv
+$ xargs -a stuff --null -s 1024
+```