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A small library for doing (command) lines.
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Cocaine Build Status

A small library for doing (command) lines.

API reference


The basic, normal stuff:

line ="echo", "hello 'world'")
line.command # => "echo hello 'world'" # => "hello world\n" 

Interpolated arguments:

line ="convert", ":in -scale :resolution :out")
line.command(:in => "omg.jpg",
             :resolution => "32x32",
             :out => "omg_thumb.jpg")
# => "convert 'omg.jpg' -scale '32x32' 'omg_thumb.jpg'"

It prevents attempts at being bad:

line ="cat", ":file")
line.command(:file => "haha`rm -rf /`.txt") # => "cat 'haha`rm -rf /`.txt'"

line ="cat", ":file")
line.command(:file => "ohyeah?'`rm -rf /`.ha!") # => "cat 'ohyeah?'\\''`rm -rf /`.ha!'"

You can ignore the result:

line ="noisy", "--extra-verbose", :swallow_stderr => true)
line.command # => "noisy --extra-verbose 2>/dev/null"

# ... and on Windows...
line.command # => "noisy --extra-verbose 2>NUL"

If your command errors, you get an exception:

line ="git", "commit")
rescue Cocaine::ExitStatusError => e
  e.message # => "Command 'git commit' returned 1. Expected 0"

If your command might return something non-zero, and you expect that, it's cool:

line ="/usr/bin/false", "", :expected_outcodes => [0, 1])
rescue Cocaine::ExitStatusError => e
  # => You never get here!

You don't have the command? You get an exception:

line ="lolwut")
rescue Cocaine::CommandNotFoundError => e
  e # => the command isn't in the $PATH for this process.

But don't fear, you can specify where to look for the command:

Cocaine::CommandLine.path = "/opt/bin"
line ="lolwut")
line.command # => "lolwut", but it looks in /opt/bin for it.

You can even give it a bunch of places to look:

    FileUtils.rm("/opt/bin/lolwut")'/usr/local/bin/lolwut') {|f| f.write('echo Hello') }
    Cocaine::CommandLine.path = ["/opt/bin", "/usr/local/bin"]
    line ="lolwut") # => prints 'Hello', because it searches the path

Or just put it in the command:

line ="/opt/bin/lolwut")
line.command # => "/opt/bin/lolwut"

You can see what's getting run. The 'Command' part it logs is in green for visibility!

line ="echo", ":var", :logger => => "LOL!") # => Logs this with #info -> Command :: echo 'LOL!'

Or log every command:

Cocaine::CommandLine.logger ="date").run # => Logs this -> Command :: date


You can potentially increase performance by installing the posix-spawn gem. This gem can keep your application's heap from being copied when forking command line processes. For applications with large heaps the gain can be significant. To include posix-spawn, simply add it to your Gemfile or, if you don't use bundler, install the gem.


Cocaine will attempt to choose from among 3 different ways of running commands. The simplest is using backticks, and is the default in 1.8. In Ruby 1.9, it will attempt to use Process.spawn. And, as mentioned above, if the posix-spawn gem is installed, it will attempt to use that. If for some reason one of the .spawn runners don't work for you, you can override them manually by setting a new runner, like so:

Cocaine::CommandLine.runner =

And if you really want to, you can define your own Runner, though I can't imagine why you would.

JRuby Caveat

If you get Error::ECHILD errors and are using JRuby, there is a very good chance that the error is actually in JRuby. This was brought to our attention in and probably fixed in You will want to use the BackticksRunner if you are unable to update JRuby.


So, here's the thing about REE: The specs that involve timeouts don't work there. Not because the logic is unsound, but because the command runs really slowly. The test passes -- eventually. This was verified using an external debugger: the process that REE kicks off in the tests reads and writes surprisingly slowly. For this reason, we cannot recommend using Cocaine with REE anymore.

It's not something we like, so if anyone has any insight into this problem, we'd love to hear about it. But, for the time being, we'll consider it more appropriate to just not use it anymore. Upgrade to 1.9.3, people.


Security concerns must be privately emailed to

Question? Idea? Problem? Bug? Comment? Concern? Like using question marks?

GitHub Issues For All!


Copyright 2011-2012 Jon Yurek and thoughtbot, inc. This is free software, and may be redistributed under the terms specified in the LICENSE file.

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