par

Run commands from stdin in parallel.

Each command is a single line terminated by the newline character (\n).

By default, the commands are run in a shell. The default number of parallel processes equals the number of CPUs (or cores).

The flag -n enables dry run mode: commands are printed to stderr but not run.

The flag -v enables verbose mode: commands are printed to stderr when run.

Installation

$ go install github.com/jabolopes/par

Example

Copy and convert a bunch of CR2 photographs to JPEG in parallel:

$ for i in *.CR2; do echo convert /run/media/$USER/EOS_DIGITAL/DCIM/100EOS5D/$i ~/fotos/$(basename $i | sed -n "s/CR2$/jpg/p"); done | par -v

Alternatives

Why not xargs?

I can never remember the xargs flags by heart and the defaults seem to be opposite of what I'm trying to achieve in terms of parallelization. Also, subshelling doesn't work as expected since the subshelling occurs before xargs executes not after, therefore, subshelling cannot use the items read by xargs. There's probably a solution to that problem but I didn't figure it out.

Why not GNU parallel?

In addition to the same subshelling problem as xargs, there's also the issues 1, 2, and 3, etc.