How to Call Shell Commands from Ruby

How to call shell commands from Ruby

This explanation is based on a commented Ruby script from a friend of mine. If you want to improve the script, feel free to update it at the link.

First, note that when Ruby calls out to a shell, it typically calls /bin/sh, not Bash. Some Bash syntax is not supported by /bin/sh on all systems.

Here are ways to execute a shell script:

cmd = "echo 'hi'" # Sample string that can be used

Kernel#` , commonly called backticks – `cmd`
This is like many other languages, including Bash, PHP, and Perl.
Returns the result (i.e. standard output) of the shell command.
Docs: http://ruby-doc.org/core/Kernel.html#method-i-60
```
value = `echo 'hi'`
value = `#{cmd}`
```
Built-in syntax, %x( cmd )
Following the x character is a delimiter, which can be any character.
If the delimiter is one of the characters (, [, {, or <,
the literal consists of the characters up to the matching closing delimiter,
taking account of nested delimiter pairs. For all other delimiters, the
literal comprises the characters up to the next occurrence of the
delimiter character. String interpolation #{ ... } is allowed.
Returns the result (i.e. standard output) of the shell command, just like the backticks.
Docs: https://docs.ruby-lang.org/en/master/syntax/literals_rdoc.html#label-Percent+Strings
```
value = %x( echo 'hi' )
value = %x[ #{cmd} ]
```
Kernel#system
Executes the given command in a subshell.
Returns true if the command was found and run successfully, false otherwise.
Docs: http://ruby-doc.org/core/Kernel.html#method-i-system
```
wasGood = system( "echo 'hi'" )
wasGood = system( cmd )
```
Kernel#exec
Replaces the current process by running the given external command.
Returns none, the current process is replaced and never continues.
Docs: http://ruby-doc.org/core/Kernel.html#method-i-exec
```
exec( "echo 'hi'" )
exec( cmd ) # Note: this will never be reached because of the line above
```

Here's some extra advice:
$?, which is the same as $CHILD_STATUS, accesses the status of the last system executed command if you use the backticks, system() or %x{}.
You can then access the exitstatus and pid properties:

$?.exitstatus

For more reading see:

http://www.elctech.com/blog/i-m-in-ur-commandline-executin-ma-commands
http://blog.jayfields.com/2006/06/ruby-kernel-system-exec-and-x.html
http://tech.natemurray.com/2007/03/ruby-shell-commands.html

Execute shell commands from Ruby code

Ryan, there's several ways to call out to the system:

Backticks:
ruby -e 'p ARGV' '1 2' '3 4' # => "[\"1 2\", \"3 4\"]\n"

The %x literal (note that you can use any delimiter you like, you're not restricted to parentheses)

%x(ruby -e 'p ARGV' '1 2' '3 4') # => "[\"1 2\", \"3 4\"]\n"

The system command. The difference here is that it passes stdin / out / err on through. (the above return the stdout, this one prints it on your process' stdout).

system('ruby', '-e p ARGV', '1 2', '3 4')
# >> ["1 2", "3 4"]

And if you need more sophisticated usage, something like open3 from the stdlib has gotten me pretty far. If you really need the big guns (it doesn't sound like you do), there's a gem open4.

Edit:

It sounds like you're wanting to do something like this:

require 'open3'

bash_script = <<SCRIPT
source "$HOME/.rvm/scripts/rvm"
rvm use jruby
ruby -v
exit
SCRIPT

out, err, status = Open3.capture3 'bash', stdin_data: bash_script
puts out
# >> Using /Users/joshcheek/.rvm/gems/jruby-1.6.7
# >> jruby 1.6.7 (ruby-1.8.7-p357) (2012-02-22 3e82bc8) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_29) [darwin-x86_64-java]

But honestly, I don't think it's a good solution for your situation, because there's many legitimate ways to set up jruby for your environment. I think it would be better to just check that the limelight binary exists, and tell your user to fix their environment if it doesn't.

Run a shell script from ruby

You can do this a few different ways

Kernel.system "command"
%x[command]
`command`

How to execute shell commands from Ruby in their own shell?

As it turns out this was an Android shell screen record problem and not a Ruby problem.

Android is carrying out optimizations of recorded video length that skew my output video. It only records the video from the first UI change to the last UI change.

Ruby run shell command in a specific directory

You can use the block-version of Dir.chdir. Inside the block you are in the requested directory, after the Block you are still in the previous directory:

Dir.chdir('mydir'){
  %x[#{cmd}]
}

Ruby interactive shell commands

Original: https://stackoverflow.com/a/6488335/2724079

This can also be accomplished with IO.expect

require 'pty'
require 'expect'

PTY.spawn("play new calimero") do |reader, writer|
  reader.expect(/What is the application name/)
  writer.puts("\n")
end

This waits for the spawned process to display "What is the application name" and when it sees that prints a defined string (new line).

Ruby - Calling commands and interact with shell in Windows environment

Seems this is working under Windows too

pipe = IO.popen('your.exe', 'w+', :err => [:child, :out])
@pipe.each_line do |line|
  if /pattern matching question/ =~ line
    break
  end
end
pipe.puts('Yes')
# another test can be here
pipe.close

Wise to use with https://ruby-doc.com/stdlib/libdoc/timeout/rdoc/Timeout.html

How to Call Shell Commands from Ruby