GNU parallel

The author Ole Tange answers every question about it on Stack Exchange. What a legend!

This program makes you respect GNU make a bit more. Good old make with -j can not only parallelize, but also take in account a dependency graph.

Some examples under:

man parallel_exampes

To get the input argument explicitly job number use the magic string {}, e.g.:

printf 'a\nb\nc\n' | parallel echo '{}'

sample output:

a
b
c

To get the job number use {#} as in:

printf 'a\nb\nc\n' | parallel echo '{} {#}'

sample output:

a 1
b 2
c 3
c 3

{%} contains which thread the job running in, e.g. if we limit it to 2 threads with -j2:

printf 'a\nb\nc\nd\n' | parallel -j2 echo '{} {#} {%}'

sample output:

The percent must be a reference to "split the inputs module the number of workers", and modulo uses the % symbol in many programming languages such as C.

To pass multiple CLI argments per command you can use -X e.g.:

printf 'a\nb\nc\nd\n' | parallel -j2 -X echo '{} {#} {%}'

sample output:

a b 1 1
c d 2 2

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