You know the drill. You have to do something with a bunch of files, so you find them and use xargs to do what you will.

find -iname '*.tmp' | xargs rm

xargs assumes whitespace separated input by default, which means that if there’s a this file.tmp in there, xargs tries to do the following:

rm 'this'
rm 'file.tmp'

That fails if you’re lucky. If you aren’t, some of those files really do exist and get unintentionally deleted.

A favorable way of doing this is to remove ambiguity from the list of files you’re passing around by making sure each filename is terminated by a null byte. Because filenames on Linux can never contain NUL, programs can safely assume that any characters encountered before it are part of the filename and not a possible delimiter. The following works correctly for filenames that contain whitespace or newlines:

find -iname '*.tmp' -print0 | xargs -0 rm

This is a standard idiom in any command line user’s repertoire.

find and xargs aren’t the only two tools you’re used to that support this, though, and that lets you do some cool things with confidence.

Note: There are arguably better ways of doing this, such as using find -exec or GNU Parallel in place of xargs.

Example: Passing around filenames without their extension

You usually want to do this when you’re planning on converting one type of file to another. The basename utility that lets us strip a trailing suffix from a string supports NUL terminated output with the -z or --zero flags. I commonly convert images and video as follows:

# Repackage all '.mp4' files in the current directory as '.mkv'
basename -azs .mp4 *.mp4 | xargs -0 -I{} ffmpeg -i {}.mp4 \
                           -acodec copy \
                           -vcodec copy \
# Convert all '.png' files in the current directory to '.jpg' with the same
# name.
basename -azs .jpg *.jpg | xargs -0 -I{} convert {}.png {}.jpg

Example: Passing around files containing a search pattern

Because every single program must come up with its own name for the same thing, grep will output a null terminated list of files if you give it the -Z or --null flags on the command line. Use that to delete all files in the current working directory containing the word ‘consistency’ as follows:

grep -s -lZ 'consistency' ./* | xargs -0 rm

Keeping track of it all

Because there’s so many different flags for this, I find it helpful to mentally group programs that use the same one. Eg. the sort, uniq, sed, and basename utilities all use -z.

Be warned, these can still have different multi character flags for the same thing:

  • basename --zero
  • sort --zero-terminated
  • uniq --zero-terminated
  • sed --null-data

This is why I drink.