03-01-2019
Shell evaluation is done automatically, by the shell, before a command is run. None of these except eval do shell evaluation; eval can do so because it's actually part of the shell!
By the same ticket, ls abc* is not a feature of ls. abc* gets evaluated by the shell before ls is executed.
I'm not sure what your >stdin stdin> are about. eval does not use stdin or stdout especially, unless the command it's evaluating does. It has no limits at all. That's what makes it dangerous.
One unique feature of xargs is that it parses single and double quotes. Usually this is considered an annoyance and worked around, but this can be used to your advantage, i.e. to split strings containing quotes without resorting to eval.
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XARGS(1L) XARGS(1L)
NAME
xargs - build and execute command lines from standard input
SYNOPSIS
xargs [-0prtx] [-e[eof-str]] [-i[replace-str]] [-l[max-lines]] [-n max-args] [-s max-chars] [-P max-procs] [--null] [--eof[=eof-str]]
[--replace[=replace-str]] [--max-lines[=max-lines]] [--interactive] [--max-chars=max-chars] [--verbose] [--exit] [--max-procs=max-procs]
[--max-args=max-args] [--no-run-if-empty] [--version] [--help] [command [initial-arguments]]
DESCRIPTION
This manual page documents the GNU version of xargs. xargs reads arguments from the standard input, delimited by blanks (which can be pro-
tected with double or single quotes or a backslash) or newlines, and executes the command (default is /bin/echo) one or more times with any
initial-arguments followed by arguments read from standard input. Blank lines on the standard input are ignored.
xargs exits with the following status:
0 if it succeeds
123 if any invocation of the command exited with status 1-125
124 if the command exited with status 255
125 if the command is killed by a signal
126 if the command cannot be run
127 if the command is not found
1 if some other error occurred.
OPTIONS
--null, -0
Input filenames are terminated by a null character instead of by whitespace, and the quotes and backslash are not special (every
character is taken literally). Disables the end of file string, which is treated like any other argument. Useful when arguments
might contain white space, quote marks, or backslashes. The GNU find -print0 option produces input suitable for this mode.
--eof[=eof-str], -e[eof-str]
Set the end of file string to eof-str. If the end of file string occurs as a line of input, the rest of the input is ignored. If
eof-str is omitted, there is no end of file string. If this option is not given, the end of file string defaults to "_".
--help Print a summary of the options to xargs and exit.
--replace[=replace-str], -i[replace-str]
Replace occurences of replace-str in the initial arguments with names read from standard input. Also, unquoted blanks do not termi-
nate arguments. If replace-str is omitted, it defaults to "{}" (like for `find -exec'). Implies -x and -l 1.
--max-lines[=max-lines], -l[max-lines]
Use at most max-lines nonblank input lines per command line; max-lines defaults to 1 if omitted. Trailing blanks cause an input
line to be logically continued on the next input line. Implies -x.
--max-args=max-args, -n max-args
Use at most max-args arguments per command line. Fewer than max-args arguments will be used if the size (see the -s option) is
exceeded, unless the -x option is given, in which case xargs will exit.
--interactive, -p
Prompt the user about whether to run each command line and read a line from the terminal. Only run the command line if the response
starts with `y' or `Y'. Implies -t.
--no-run-if-empty, -r
If the standard input does not contain any nonblanks, do not run the command. Normally, the command is run once even if there is no
input.
--max-chars=max-chars, -s max-chars
Use at most max-chars characters per command line, including the command and initial arguments and the terminating nulls at the ends
of the argument strings. The default is as large as possible, up to 20k characters.
--verbose, -t
Print the command line on the standard error output before executing it.
--version
Print the version number of xargs and exit.
--exit, -x
Exit if the size (see the -s option) is exceeded.
--max-procs=max-procs, -P max-procs
Run up to max-procs processes at a time; the default is 1. If max-procs is 0, xargs will run as many processes as possible at a
time. Use the -n option with -P; otherwise chances are that only one exec will be done.
SEE ALSO
find(1L), locate(1L), locatedb(5L), updatedb(1) Finding Files (on-line in Info, or printed)
XARGS(1L)