GNU Parallel tutorial

Input sources

GNU parallel reads input from input sources. These can be files, the command line, and stdin (standard input or a pipe).

A single input source

Input can be read from the command line:

  parallel echo ::: A B C

Output (the order may be different because the jobs are run in parallel):

  A
  B
  C

The input source can be a file:

  parallel -a abc-file echo

Output: Same as above.

STDIN (standard input) can be the input source:

  cat abc-file | parallel echo

Output: Same as above.

Multiple input sources

GNU parallel can take multiple input sources given on the command line. GNU parallel then generates all combinations of the input sources:

  parallel echo ::: A B C ::: D E F

Output (the order may be different):

  A D
  A E
  A F
  B D
  B E
  B F
  C D
  C E
  C F

Source: GNU Parallel tutorial

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