Editing Xargs (section)

==Separator problem==
Many Unix utilities are line-oriented. These may work with <code>xargs</code> as long as the lines do not contain <code>'</code>, <code>"</code>, or a space. Some of the Unix utilities can use [[Null character|NUL]] as record separator (e.g. [[Perl]] (requires <code>-0</code> and <code>\0</code> instead of <code>\n</code>), <code>[[Locate (Unix)|locate]]</code> (requires using <code>-0</code>), <code>[[Find (Unix)|find]]</code> (requires using <code>-print0</code>), <code>[[grep]]</code> (requires <code>-z</code> or <code>-Z</code>), <code>[[Sort (Unix)|sort]]</code> (requires using <code>-z</code>)). Using <code>-0</code> for <code>xargs</code> deals with the problem, but many Unix utilities cannot use NUL as separator (e.g. <code>[[head (Unix)|head]]</code>, <code>[[tail (Unix)|tail]]</code>, <code>[[ls]]</code>, <code>[[echo (command)|echo]]</code>, <code>[[sed]]</code>, <code>[[tar (file format)|tar]] -v</code>, <code>[[wc (Unix)|wc]]</code>, <code>[[which (command)|which]]</code>).

But often people forget this and assume <code>xargs</code> is also line-oriented, which is '''not''' the case (per default <code>xargs</code> separates on newlines '''and''' blanks within lines, substrings with blanks must be single- or double-quoted).

The separator problem is illustrated here:
<syntaxhighlight lang="bash">
# Make some targets to practice on
touch important_file
touch 'not important_file'
mkdir -p '12" records'

find . -name not\* | tail -1 | xargs rm
find \! -name . -type d | tail -1 | xargs rmdir
</syntaxhighlight>
Running the above will cause <code>important_file</code> to be removed but will remove neither the directory called <code>12" records</code>, nor the file called <code>not important_file</code>.

The proper fix is to use the GNU-specific <code>-print0</code> option, but <code>tail</code> (and other tools) do not support NUL-terminated strings:
<syntaxhighlight lang="bash">
# use the same preparation commands as above
find . -name not\* -print0 | xargs -0 rm
find \! -name . -type d -print0 | xargs -0 rmdir
</syntaxhighlight>

When using the <code>-print0</code> option, entries are separated by a null character instead of an end-of-line. This is equivalent to the more verbose command:<syntaxhighlight lang="bash" inline>find . -name not\* | tr \\n \\0 | xargs -0 rm</syntaxhighlight> or shorter, by switching <code>xargs</code> to (non-POSIX) '''line-oriented mode''' with the <code>-d</code> (delimiter) option: <syntaxhighlight lang="bash" inline>find . -name not\* | xargs -d '\n' rm</syntaxhighlight>

but in general using <code>-0</code> with <code>-print0</code> should be preferred, since newlines in filenames are still a problem.

GNU <code>[[GNU parallel|parallel]]</code> is an alternative to <code>xargs</code> that is designed to have the same options, but is line-oriented. Thus, using GNU Parallel instead, the above would work as expected.<ref>[https://www.gnu.org/software/parallel/man.html#differences_between_xargs_and_gnu_parallel Differences Between xargs and GNU Parallel]. [http://www.gnu.org GNU.org]. Accessed February 2012.</ref>

For Unix environments where <code>xargs</code> does not support the <code>-0</code> nor the {{code|-d}} option (e.g. Solaris, AIX), the POSIX standard states that one can simply backslash-escape every character:<syntaxhighlight lang="bash" inline>find . -name not\* | sed 's/\(.\)/\\\1/g' | xargs rm</syntaxhighlight>.<ref>{{man|1|xargs|SUS}}</ref> Alternatively, one can avoid using xargs at all, either by using GNU parallel or using the {{code|-exec ... +}} functionality of {{code|find}}.