JosephPecoraro · March 19, 2025 06:46 · starkcoffee · Jun 14, 2012 · JosephPecoraro · Jun 14, 2012
diff --git a/shell-execution.rb b/shell-execution.rb
 # Ways to execute a shell script in Ruby
 # Example Script - Joseph Pecoraro

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

 # 1. Kernel#` - commonly called backticks - `cmd` 
 # This is like many other languages, including bash, PHP, and Perl
 #   Synchronous (blocking)
 #   Returns the output of the shell command
 #   Docs: http://ruby-doc.org/core/classes/Kernel.html#M001111

 value = `echo 'hi'` # or uglier but valid => Kernel.`("echo 'hi'")
 value = `#{cmd}`    # or uglier but valid => Kernel.`("#{cmd}")


 # 2. 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.
 #   Synchronous (blocking)
 #   Returns the output of the shell command, just like the backticks
 #   Docs: http://www.ruby-doc.org/docs/ProgrammingRuby/html/language.html

 value = %x( echo 'hi' )
 value = %x[ #{cmd} ]


 # 3. Kernel#system
 # Executes the given command in a subshell
 #   Synchronous (blocking)
 #   Return: true if the command was found and ran successfully, false otherwise
 #   Docs: http://ruby-doc.org/core/classes/Kernel.html#M002992

 wasGood = system( "echo 'hi'" )
 wasGood = system( cmd )


 # 4. Kernel#exec
 # Replaces the current process by running the given external command.
 #   Synchronous (never returns)
 #   Return: none, the current process is replaced and never continues
 #   Docs: http://ruby-doc.org/core/classes/Kernel.html#M002992

 exec( "echo 'hi'" )
 exec( cmd ) # Note: this will never be reached beacuse of the line above


 # 5. IO.popen
 # Runs the specified command as a subprocess; the subprocess's standard
 # input and output will be connected to the returned IO object. This
 # allows you to provide STDIN input and get STDOUT output easily.
 #   Asynchronous (IO objects)
 #   Return: IO object, (IO#pid, IO#read)
 #   Docs: https://www.rubydoc.info/stdlib/core/IO.popen

 io = IO.popen("echo 'hi'") # Or IO.popen(["echo", "hi"])
 io = IO.popen(cmd)

 IO.popen(["echo", "'hi'"]) do |io|
  # ...
 end


 # 6. open3
 # Runs the specified command as a subprocess; the subprocess's standard
 # input, stdout, and stderr IO objects are available. There is also
 # an "open4" gem to more easily get the PID of the child process.
 #   Synchronous (get strings) or Asynchronous (IO objects)
 #   Return: Strings (capture*) or IO objects (popen*)
 #   Docs: https://docs.ruby-lang.org/en/2.5.0/Open3.html#method-c-popen3

 require 'open3'
 stdin_io, stdout_io, stderr_io, process_waiter = Open3::popen3(cmd)
 stdout_str, stderr_str, process_info = Open3::capture3(cmd)

 require 'open4'
 pid, stdin, stdout, stderr = Open4::popen4(cmd);


 # Extra Advice - Exit Code
 # $? which is the same as $CHILD_STATUS (if you require 'english')
 # 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
 #   Docs: https://ruby-doc.org/core-2.7.1/Process/Status.html#method-i-exitstatus

 $?.exitstatus


 # Extra Advice - Escaping
 # When running shell commands, it is often important to escape
 # characters that would have special meanings (quotes, $, spaces, etc).
 # Ruby makes this simple with the Shellwords module.
 #   Docs: https://ruby-doc.org/stdlib-2.5.3/libdoc/shellwords/rdoc/Shellwords.html#method-c-shellescape

 require 'shellwords'
 path = "/path/to a/file" # This has a space that should be escaped properly.
 %x{ cat #{Shellwords.escape(path)} }


 # Extra Advice - String#chomp
 # Shell commands typically end with a newline which you will often want
 # to get rid of. Ruby makes this simple with `chomp`.
 #   Docs: https://ruby-doc.org/core-2.7.2/String.html#method-i-chomp

 str = `echo 42`       # => "42\n"
 str = `echo 42`.chomp # => "42"


 # More Reading
 # https://stackoverflow.com/questions/2232/how-to-call-shell-commands-from-ruby/2280#2280
 # 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
	# Ways to execute a shell script in Ruby
	# Example Script - Joseph Pecoraro

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

	# 1. Kernel#` - commonly called backticks - `cmd`
	# This is like many other languages, including bash, PHP, and Perl
	# Synchronous (blocking)
	# Returns the output of the shell command
	# Docs: http://ruby-doc.org/core/classes/Kernel.html#M001111

	value = `echo 'hi'` # or uglier but valid => Kernel.`("echo 'hi'")
	value = `#{cmd}` # or uglier but valid => Kernel.`("#{cmd}")


	# 2. 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.
	# Synchronous (blocking)
	# Returns the output of the shell command, just like the backticks
	# Docs: http://www.ruby-doc.org/docs/ProgrammingRuby/html/language.html

	value = %x( echo 'hi' )
	value = %x[ #{cmd} ]


	# 3. Kernel#system
	# Executes the given command in a subshell
	# Synchronous (blocking)
	# Return: true if the command was found and ran successfully, false otherwise
	# Docs: http://ruby-doc.org/core/classes/Kernel.html#M002992

	wasGood = system( "echo 'hi'" )
	wasGood = system( cmd )


	# 4. Kernel#exec
	# Replaces the current process by running the given external command.
	# Synchronous (never returns)
	# Return: none, the current process is replaced and never continues
	# Docs: http://ruby-doc.org/core/classes/Kernel.html#M002992

	exec( "echo 'hi'" )
	exec( cmd ) # Note: this will never be reached beacuse of the line above


	# 5. IO.popen
	# Runs the specified command as a subprocess; the subprocess's standard
	# input and output will be connected to the returned IO object. This
	# allows you to provide STDIN input and get STDOUT output easily.
	# Asynchronous (IO objects)
	# Return: IO object, (IO#pid, IO#read)
	# Docs: https://www.rubydoc.info/stdlib/core/IO.popen

	io = IO.popen("echo 'hi'") # Or IO.popen(["echo", "hi"])
	io = IO.popen(cmd)

	IO.popen(["echo", "'hi'"]) do \|io\|
	# ...
	end


	# 6. open3
	# Runs the specified command as a subprocess; the subprocess's standard
	# input, stdout, and stderr IO objects are available. There is also
	# an "open4" gem to more easily get the PID of the child process.
	# Synchronous (get strings) or Asynchronous (IO objects)
	# Return: Strings (capture) or IO objects (popen)
	# Docs: https://docs.ruby-lang.org/en/2.5.0/Open3.html#method-c-popen3

	require 'open3'
	stdin_io, stdout_io, stderr_io, process_waiter = Open3::popen3(cmd)
	stdout_str, stderr_str, process_info = Open3::capture3(cmd)

	require 'open4'
	pid, stdin, stdout, stderr = Open4::popen4(cmd);


	# Extra Advice - Exit Code
	# $? which is the same as $CHILD_STATUS (if you require 'english')
	# 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
	# Docs: https://ruby-doc.org/core-2.7.1/Process/Status.html#method-i-exitstatus

	$?.exitstatus


	# Extra Advice - Escaping
	# When running shell commands, it is often important to escape
	# characters that would have special meanings (quotes, $, spaces, etc).
	# Ruby makes this simple with the Shellwords module.
	# Docs: https://ruby-doc.org/stdlib-2.5.3/libdoc/shellwords/rdoc/Shellwords.html#method-c-shellescape

	require 'shellwords'
	path = "/path/to a/file" # This has a space that should be escaped properly.
	%x{ cat #{Shellwords.escape(path)} }


	# Extra Advice - String#chomp
	# Shell commands typically end with a newline which you will often want
	# to get rid of. Ruby makes this simple with `chomp`.
	# Docs: https://ruby-doc.org/core-2.7.2/String.html#method-i-chomp

	str = `echo 42` # => "42\n"
	str = `echo 42`.chomp # => "42"


	# More Reading
	# https://stackoverflow.com/questions/2232/how-to-call-shell-commands-from-ruby/2280#2280
	# 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