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xargs

xargs

xargs (short for "eXtended ARGuments") converts input from stdin into arguments to a command.

Unlike grep or awk which can take input either as command-line arguments or stdin, commands like rm, cp or echo can only take input as arguments, which is why xargs is necessary.

Basic usage

xargs [options] [command [initial-arguments]]

find /path -type f -name '*.js' | xargs rm
# Find all files ending in `.js` in `/path` and remove them

find . -name '*.py' | xargs wc -l
# Recursively find Python files and count number of lines in them

find . -name '*.json' | xargs grep 'user'
# Recursively find JSON files and search them for `user`

Separator problem

Line-oriented utilities will work with xargs as long as records do not contain spaces in them. But since xargs is not line-oriented (by default, it separates on newlines and blanks within lines), it may treat a single record as separate.

If records do contain spaces, you must use NUL as the record separator. This can be set using

  • -0 for Perl,
  • -0 for locate,
  • -z/-Z for grep,
  • -z for sort,
  • -print0 for find

And then use the -0 option with xargs:

find . -name "*.txt" -print0 | xargs -0 rm
# Separate entries by `NUL` instead of a newline

find . -name "*.txt" -print0 | xargs -d '\n' rm
# Equivalent to above, `-0` is preferred since this won't work on filenames with newline

Placement of arguments

To insert the listed arguments at some position other than the end of the command line, pass a string to the -I option that will be replaced with the supplied input.

find /path -type f -name '*~' -print0 | xargs -0 -I % cp -a % ~/backups

Operating on a subset of arguments at a time

echo {0..9} | xargs -n 2 # Break up the input into two arguments per line
# Useful for commands like `diff` that operate on 2 files at time

Parallelize operations

time echo {1..5} | xargs -n 1 -P 5 sleep # ~5 seconds
time echo {1..5} | xargs -n 1 sleep # ~15 seconds

find /path -name '*.foo' | xargs -P 24 -I '{}' /cpu/bound/process '{}' -o '{}'.out
# Queue 24 processes and wait on each to finish before launching another
# To ensure output streams are synchronized, use `--output file` where possible

GNU parallel

GNU parallel is an alternative to xargs that is designed to have the same options, but is line-oriented.

It does have the -0 option like xargs but it is only needed if there are newlines in filenames you are dealing with.