Run several commands in parallel

par is a small utility that runs multiple commands in parallel and by default exits with a failure status of a first failure it sees.

Use --help for command-line help.

Basic usage example

> par "echo foo; sleep 1; echo foo; sleep 1; echo foo" "echo bar; sleep 1; echo bar; sleep 1; echo bar" && echo "success"
foo
bar
bar
foo
bar
foo
success
> par "echo foo; sleep 1; foofoo" "echo bar; sleep 1; echo bar; sleep 1; echo bar" && echo "success"
bar
foo
bar
/bin/sh: foofoo: command not found
bar

Adding prefix to output

> par "PARPREFIX=[fooechoer] echo foo" "echo bar"
[fooechoer] foo
bar

Force success exit-code

> par --succeed "foo" "bar" && echo 'wow'
/bin/sh: foo: command not found
/bin/sh: bar: command not found
wow

Installation

For Ubuntu 12.04, 14.04 and MacOS X download some release and put it into $PATH. For others -- see "building from source" instructions.

https://github.com/k-bx/par/releases

Example:

cd /tmp
wget https://github.com/k-bx/par/releases/download/1.0.1/par-ubuntu-12.04
sudo mv ./par-ubuntu-12.04 /usr/local/bin/

Building from source

1. Install Haskell's GHC compiler
2. run make. Produced executable will be inside ./dist/build/par/par
3. optionally, run sudo make install to copy into /usr/local/bin/

Please note that par uses specific set of versions to build, setting them via cabal.config file. If you want to remove these constraints, just remove the file.

Footnote on strings in bash/zsh

Many people know that strings in bash and zsh are "weird", but not many people know that there are good old ASCII-strings also present.

Double-quoted strings are interpolating variables and do other interesting things like reacting on "!" sign, for example.

Single-quotes don't interpolate variables and don't react on "!" sign, but they also don't let you quote neither single-quote nor double-quote.

Turns out good old ASCII-quotes are available as $'string' syntax! Example:

> echo $'foo'
foo
> echo $'foo with "doublequotes and \'singletuoes\' inside"!'
foo with "doublequotes and 'singletuoes' inside"!

You are a better person with this knowledge now. $'Enjoy!'