How to ignore xargs commands if stdin input is empty?

For GNU xargs, you can use the -r or --no-run-if-empty option:

--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. This option is a GNU extension.

Users of non-GNU xargs may take advantage of -L <#lines>, -n <#args>, -i, and -I <string>:

ls /empty_dir/ | xargs -n10 chown root # chown executed every 10 args or fewerls /empty_dir/ | xargs -L10 chown root # chown executed every 10 lines or fewerls /empty_dir/ | xargs -i cp {} {}.bak # every {} is replaced with the args from one input linels /empty_dir/ | xargs -I ARG cp ARG ARG.bak # like -i, with a user-specified placeholder

Keep in mind that xargs splits the line at whitespace but quoting and escaping are available; RTFM for details.

Also, as Doron Behar mentions, this workaround isn't portable so checks may be needed:

$ uname -isSunOS sun4v$ xargs -n1 echo blah < /dev/null

$ uname -isLinux x86_64$ xargs --version | head -1xargs (GNU findutils) 4.7.0-git$ xargs -n1 echo blah < /dev/nullblah

man xargs says --no-run-if-empty.