Run System Command in Ruby and Interact with It

Run system command in ruby and interact with it

The Unix way to handle these situations is with expect, which Ruby comes with built-in support for:

require 'pty'
require 'expect'

PTY.spawn("your command here") do |reader, writer|
  reader.expect(/Use this key anyway/, 5) # cont. in 5s if input doesn't match
  writer.puts('y')
  puts "cmd response: #{reader.gets}"
end

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

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

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).

Getting output of system() calls in Ruby

I'd like to expand & clarify chaos's answer a bit.

If you surround your command with backticks, then you don't need to (explicitly) call system() at all. The backticks execute the command and return the output as a string. You can then assign the value to a variable like so:

output = `ls`
p output

printf output # escapes newline chars

How do I use the system() command to pass in user input?

You should look into the Open3 library from the Ruby stdlib. It gives you more control over "shelling out".

output, status = Open3.capture2("./script", :stdin_data => "I am STDIN")

Run a command in current terminal in ruby then execute code when it exits

Thanks a lot to hek2mgl for pointing in the right direction:

include Signal
include Process

# Handling SIGINT by doing nothing prevents default behaviour
# (killing both processes)
Signal.trap("INT") {}

# Fork off subprocess (so exec won't exit from your main process)
pid = fork
if pid == nil then
  # Child code. Use exec(!) to avoid the signal handler
  # getting called in the child.
  exec 'heroku run console'
else
  # Wait for subprocess to exit
  wait pid
  # "wait" sets the $? according to the subprocess exit status
  exit_status = $?.exitstatus

  p "Execute more ruby code"
  exit exit_status
end

Run System Command in Ruby and Interact with It