Skip to content


Subversion checkout URL

You can clone with
Download ZIP
A small library for doing (command) lines.

String conversion as a one-liner

Just cleaning up.
latest commit 2a89b71e50
@sapslaj sapslaj authored jyurek committed

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!'"

NOTE: It only does that for arguments interpolated via run, NOT arguments passed into new (see 'Security' below):

line ="echo", "haha`whoami`")
line.command # => "echo haha`whoami`" # => "hahawebserver"

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


Short version: Only pass user-generated data into the run method and NOT new.

As shown in examples above, Cocaine will only shell-escape what is passed in as interpolations to the run method. It WILL NOT escape what is passed in to the second argument of new. Cocaine assumes that you will not be manually passing user-generated data to that argument and will be using it as a template for your command line's structure.


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 issues


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.

Spawn warning

If you get unsupported spawn option: out warning (like in issue 38), try to use PopenRunner:

Cocaine::CommandLine.runner =

Thread Safety

Cocaine should be thread safe. As discussed here, in this climate_control thread, climate_control, which modifies the environment under which commands are run for the BackticksRunner and PopenRunner, is thread-safe but not reentrant. Please let us know if you find this is ever not the case.


Security concerns must be privately emailed to

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

GitHub Issues For All!


Thank you to all the contributors!


Cocaine is maintained and funded by thoughtbot, inc

The names and logos for thoughtbot are trademarks of thoughtbot, inc.


Copyright 2011-2014 Jon Yurek and thoughtbot, inc. This is free software, and may be redistributed under the terms specified in the LICENSE file.

Something went wrong with that request. Please try again.