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I have been trying to work on my own little backup script. I am running into an issue when I run my script and the rm command has nothing to do. I would still like to process the output (aka display different messages according to whether or not the operation has failed) but suppress the output natively generated by rm. Currently this:
ls -t | tail -n +$startnumber | xargs -d '\n' rm && echo "Removed old backup(s)." || echo "No more than $keepnumber files; nothing to do."
unfortunately outputs this:
rm: missing operand Try 'rm --help' for more information. No more than 14 files; nothing to do.
Where I would like to get rid of the first two lines and only output my own, "more legible" message. I have tried using rm -f but this will always (and falsely) trigger the successful output.

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up vote 0 down vote accepted

These rm messages were sent to standard error (stderr). You can redirect the standard error output (stderr) to /dev/null like:

xargs -d '\n' rm 2>/dev/null

This will prevent both the lines from printed on your terminal and only your customized message will appear.

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Thank you, this solved the issue. I was redirecting the stdout rather than the stderr in my attempts (I omitted the "2"). – mti_ 2 days ago
up vote 0 down vote

I would just save the file listing in a temporary file, and count the lines there, before trying to rm. (Or just count the files otherwise first.)

You could also redirect errors from rm to /dev/null, but that would mask valid errors too.

Say

tmpfile=$(mktemp)
ls -t | tail -n +$startnumber > $tmpfile
if [ -s "$tmpfile" ] ; then
    echo not empty, do something with filelist in $tmpfile
else
    echo empty, do something else
fi
rm "$tmpfile"

Of course, using ls like that will break if you have file names containing newlines for some reason. (Yes, it's possible. Though in this case it would just mean that some files are not removed even though they should be.)

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