GNU parallel

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Parallel
Gnu-parallel.png
Developer(s) GNU Project
Stable release 20130922[1] / September 21, 2013; 11 months ago (2013-09-21)
Written in Perl
Operating system GNU
Type Utility
License GPLv3
Website www.gnu.org/software/parallel/

GNU parallel is a command-line driven utility for Linux or other Unix-like operating systems which allows the user to execute shell scripts in parallel. GNU parallel is free software, written by Ole Tange in Perl. It is available under the terms of GPLv3.[2]

Usage[edit]

The most common usage is to replace the shell loop, for example

    for x in `cat list` ; do 
        do_something "$x"
    done | process_output

to the form of

    cat list | parallel do_something | process_output

where the file list contains arguments for do_something and where process_output may be empty.

Scripts using parallel are often easier to read than scripts using pexec.

The program parallel features also

  • grouping of standard output and standard error so the output of the parallel running jobs do not run together;
  • retaining the order of output to remain the same order as input;
  • dealing nicely with file names containing special characters such as space, single quote, double quote, ampersand, and UTF-8 encoded characters;

By default, parallel runs as many jobs in parallel as there are CPU cores.

An introduction video to GNU Parallel can be found on Wikimedia Commons.

Examples[edit]

 find . -name "*.foo" | parallel grep bar

The above is the parallel equivalent to:

 find . -name "*.foo" -exec grep bar {} +

This searches in all files in the current directory and its subdirectories whose name end in .foo for occurrences of the string bar. The parallel command will work as expected unless a file name contains a newline. In order to avoid this limitation one may use:

 find . -name "*.foo" -print0 | parallel -0 grep bar

The above command uses the null character to delimit file names.

 find . -name "*.foo" | parallel -X mv {} /tmp/trash

The above command uses {} to tell parallel to replace {} with the argument list.

 find . -maxdepth 1 -type f -name "*.ogg" | parallel -X -r cp -v -p {} /home/media

The command above does the same as:

 cp -v -p *.ogg /home/media

however, the former command which uses find/parallel/cp is more resource efficient and will not halt with an error if the expansion of *.ogg is too large for the shell.

See also[edit]

References[edit]

External links[edit]