prevent xargs from quitting on error

Question

According to the man page, xargs will quit if one of the execution lines exits with an error of 255:

If any invocation of the command exits with a status of 255, xargs will stop immediately without reading any further input. An error message is issued on stderr when this happens.

How can I get xargs to not do this?

I have a 1500 or so line batch job that I want to run, 50 lines at a time. I was finding that it was always dying at a certain line, and not completing the job. Not good!

An even better question, the question describing what I am trying to do, is:

How can I run a 1500 line batch script, 50 lines at a time, so that it does not quit the job in the middle, and so that the output is captured to a log file of some kind?

Answer 1

You could wrap the perl script with another simple bash script:

#!/bin/bash
real-command "$@" || exit 0

This will call real-command passing it all the parameters that you pass to this fake-command and it will always return a 0 exit code (that means it is always successful) and xargs will never stop with this.

Answer 2

Similar to larsks answer but more explicit:

xargs sh -c "somecommand || true"

Answer 3

Just found a fun answer to this one, though its usefulness will depend on the command you're trying to run.

If you're using xargs to basically assemble a list of commands, you can get this behavior by telling xargs to echo the command, then piping to bash.

For example, if you're trying to delete a list of things that may or may not exist:

# presume this will fail in a similar way to your command
cat things_to_delete | xargs -n1 delete_command_that_might_exit

# instead echo the commands and pipe to bash
cat things_to_delete | xargs -n1 echo delete_command_that_might_exit | bash

This works because, first, xargs is only ever calling echo, so it won't see any errors. Then second, because bash's default behavior to continue execution after a failed statement.

To be more specific about my case, I was using this to remove a bunch of old application versions from AWS ElasticBeanstalk like so:

aws elasticbeanstalk describe-application-versions --application-name myapp |\
jq -r '.ApplicationVersions | sort_by(.DateCreated) | .[0:-10] | .[].VersionLabel' |\
xargs -n1 \
  echo aws elasticbeanstalk delete-application-version \
       --delete-source-bundle --application-name myapp --version-label |\
bash

Answer 4

You could write your xargs invocation to mask the return codes of your command lines. With something like the following,xargs will never see exit codes return by somecommand:

xargs sh -c "somecommand || :"

Answer 5

Following construction works for me:

ls | xargs -I % svn upgrade %

Even if svn upgrade failed on some element, process was continued

Answer 6

If you were using xargs with find, use the -exec option of find instead:

find . -name '*.log' -exec somecommand {} \;