Rubysh: Ruby subprocesses made easy

Rubysh makes shelling out easy with a sh-like syntax layer for Ruby:

irb -r rubysh
>> command = Rubysh('echo', 'hello-from-Rubysh') | Rubysh('grep', '--color', 'Rubysh')
>> command.run
hello-from-Rubysh
=> Rubysh::Runner: echo hello-from-Rubysh | grep --color Rubysh (exitstatus: 0)

Rubysh's philosophy is to make simple tasks simple and complex tasks possible.

Motivation

Existing Ruby shell libaries make it very difficult to do tasks that are simple in sh, such as:

• piping the output from one program to another
• redirecting a program's output to a file
• use a pre-tokenized array of arguments

(Some existing libraries make some of these tasks easy, but not all of them at once.) Rubysh tries to emulate sh's interface and semantics as closely as possible.

Features

Redirecting a file descriptor to a file:

# echo hello-from-Rubysh >/tmp/file.txt
Rubysh('echo', 'hello-from-Rubysh', Rubysh.stdout > '/tmp/file.txt')
Rubysh('echo', 'hello-from-Rubysh', Rubysh::FD(1) > '/tmp/file.txt')

Redirecting a file descriptor to another file descriptor:

# echo hello-from-Rubysh 2>&1
Rubysh('echo', 'hello-from-Rubysh', Rubysh.stderr > Rubysh.stdout)

Feeding standard input with a string literal:

# cat <<< "hello there"
Rubysh('cat', Rubysh.<<< 'hello there')

Rubysh has been written to work with arbitrary file descriptors, so you can do the same advanced FD redirection magic you can in sh:

# cat 3<<< "hello there" <&3
Rubysh('cat', Rubysh::FD(3).<<< 'hello there', Rubysh.stdin < Rubysh::FD(3))

You can also capture output to a named target (here :stdout, :stderr are arbitrary symbols):

command = Rubysh('echo', 'hi', Rubysh.stdout > :stdout, Rubysh.stderr > :stderr)
runner = command.run
runner.read(:stdout) # "hi\n"
runner.read(:stderr) # ""

You can also have your child run a Ruby block rather than execute a command:

command = Rubysh(Rubysh.stdout > :stdout) {puts "hi from child"}
runner = command.run
runner.read(:stdout) # "hi from child\n"

Controlled input

You can easily read and write data interactively:

>> runner = Rubysh('examples/dots.sh', Rubysh.>).run_async
=> Rubysh::Runner: examples/dots.sh >:stdout (readers: :stdout, pid: 78296)
>> runner.read(:how => :partial) # block until some output available
=> ".\n.\n.\n.\n.\n.\n.\n.\n.\n"
>> runner.read(:how => :nonblock)
=> nil
>> runner.read # block until all output available
=> ".\n[...]"

Reactive output

You can also receive real-time notifications as data becomes available:

>> runner = Rubysh(
    'examples/on_read_example.sh',
     Rubysh.stdout > :stdout, Rubysh.stderr > :stderr,
     on_read: Proc.new {|target, data| puts "[#{target}]: #{data}"}
    )
=> Command: examples/on_read_example.sh >:stdout 2>:stderr {:on_read=>#<Proc:0x007f8ad3bc5790@(irb):4>}
>> runner.run
[stdout]: [1] Hello from stdout
[stderr]: [1] Hello from stderr
[stdout]: [2] Hello from stdout
[stderr]: [2] Hello from stderr
[...]

API

The Rubysh helper function produces instances of BaseCommand. You can run run on these to spawn a subprocess and then wait for it to complete. Alternatively, you can do:

command = Rubysh('ls')
runner = command.run_async
runner.wait

If you don't want to type Rubysh all the time, you can alias it with the AliasRubysh helper:

AliasRubysh(:R)
R('ls')

Safety

Rubysh takes a splatted array argument as a command specification. In particular, it doesn't convert it back and forth a command-line string, meaning you don't have to worry about spaces in arguments. (You should still always think twice before putting untrusted arguments into a shell argument.)

Installation

Rubysh is hosted on Rubygems. You can install by adding this line to your application's Gemfile:

gem 'rubysh'

Or by installing directly via

$ gem install rubysh

Contributing

Patches welcome! I'm happy to merge pull requests.

Future features

• Better support for streaming output
• Subshell syntax (cat <(ls), echo $(ls))