= GNU parallel
{tag=Good}
{tag=GNU package}
{wiki}
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:
``
a 1 1
b 2 1
c 3 2
d 4 1
``
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 (language)>.
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
``