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parcat - cat files or fifos in parallel


parcat [--rm] [-#] file(s) [-#] file(s)


GNU parcat reads files or fifos in parallel. It writes full lines so there will be no problem with mixed-half-lines which you risk if you use:

   (cat file1 & cat file2 &) | ...

Arguments can be given on the command line or passed in on stdin (standard input).



Arguments following this will be sent to the file descriptor #. E.g.

  parcat -1 stdout1 stdout2 -2 stderr1 stderr2

will send stdout1 and stdout2 to stdout (standard output = file descriptor 1), and send stderr1 and stderr2 to stderr (standard error = file descriptor 2).


Remove files after opening. As soon as the files are opened, unlink the files.


Simple line buffered output

GNU parallel saves output to tempfiles. If the amount of data is bigger than the free disk space, then you can use this technique to do line buffering without saving to disk:

  mkfifo slot-{1..5}
  seq 10000000 | parallel -j5 --round --pipe 'cat > slot-{%}' &
  parcat slot-{1..5} | wc


GNU parcat is part of GNU parallel. Report bugs to <bug-parallel@gnu.org>.


Copyright (C) 2016-2019 Ole Tange, http://ole.tange.dk and Free Software Foundation, Inc.


This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or at your option any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.

Documentation license I

Permission is granted to copy, distribute and/or modify this documentation under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the file fdl.txt.

Documentation license II

You are free:

to Share

to copy, distribute and transmit the work

to Remix

to adapt the work

Under the following conditions:


You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work).

Share Alike

If you alter, transform, or build upon this work, you may distribute the resulting work only under the same, similar or a compatible license.

With the understanding that:


Any of the above conditions can be waived if you get permission from the copyright holder.

Public Domain

Where the work or any of its elements is in the public domain under applicable law, that status is in no way affected by the license.

Other Rights

In no way are any of the following rights affected by the license:


For any reuse or distribution, you must make clear to others the license terms of this work.

A copy of the full license is included in the file as cc-by-sa.txt.


GNU parcat uses Perl.


cat(1), parallel(1)