Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
Shell Execution in Ruby
# 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
# Returns the result 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.
# Returns the result 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
# 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.
# 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
# Extra Advice
# $? 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
$?.exitstatus
# More Reading
# 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
@starkcoffee

This comment has been minimized.

Copy link

commented Jun 14, 2012

awesome summary - thanks!

@JosephPecoraro

This comment has been minimized.

Copy link
Owner Author

commented Jun 14, 2012

@sivakumar-kailasam

This comment has been minimized.

Copy link

commented Jun 17, 2012

Liked the extra advice :)

@devilankur18

This comment has been minimized.

Copy link

commented Aug 24, 2012

Just Awsesome

@marksliva

This comment has been minimized.

Copy link

commented Sep 18, 2013

Thank you!

@cizixs

This comment has been minimized.

Copy link

commented Nov 15, 2013

Very useful , Thx!

@NeWbLt123

This comment has been minimized.

Copy link

commented Mar 21, 2014

Thanks, very helpful !

@mx4492

This comment has been minimized.

Copy link

commented Apr 14, 2014

In case you need to drop the ball when the command fails, https://github.com/mx4492/simple_cmd

@chrishough

This comment has been minimized.

Copy link

commented Jun 5, 2014

thanks man!

@barbolo

This comment has been minimized.

Copy link

commented Jun 12, 2015

I'd suggest you to check https://github.com/rtomayko/posix-spawn if you are having memory/latency issues when executing shell commands.

@yanbit

This comment has been minimized.

Copy link

commented Aug 14, 2015

thanks man!

@kassane

This comment has been minimized.

Copy link

commented Aug 29, 2015

Awesome man!

@dminca

This comment has been minimized.

Copy link

commented Sep 18, 2015

Thanks man, very interesting and useful 👍

@mika-cn

This comment has been minimized.

Copy link

commented Dec 25, 2015

Awesome man! thanks

@mkows

This comment has been minimized.

Copy link

commented Jan 19, 2016

@JosephPecoraro thanks for sharing that! Any idea how to get rid of trailing "\n"?

$ cd /tmp
tmp$ irb
irb(main):001:0> `pwd`
=> "/tmp\n"
irb(main):002:0>  %x( pwd )
=> "/tmp\n"

One way to achieve this is:

`pwd`[0..-2]
=> "/tmp"

But I am wondering if there's nicer way to do it.

@jerry-tao

This comment has been minimized.

Copy link

commented Feb 10, 2016

@mkowaliszyn The backticks just simple redirect the stdout to the result. With the default way of backticks it won't get rid of \n for you.

You can just call strip to trim the \n.

Say

 `pwd`.strip.

With more than 1 line result you can:

`ls`.split("\n")
@JosephPecoraro

This comment has been minimized.

Copy link
Owner Author

commented Aug 12, 2016

@mkows late reply, but yes! String#chomp is a convenient method that exists for just such cases! It removes all trailing newlines from the string:

irb(main):001:0> `pwd`
=> "/tmp\n"
irb(main):002:0> `pwd`.chomp
=> "/tmp"

Very similar to strip / rstrip mention above.

@wellavelino

This comment has been minimized.

Copy link

commented Nov 30, 2016

Thaaanks!

@diboanches

This comment has been minimized.

Copy link

commented Apr 25, 2017

OSOM! Спасибо!

@ArtiusAstro

This comment has been minimized.

Copy link

commented Sep 3, 2017

Awesome stuff!

@Skalnark

This comment has been minimized.

Copy link

commented Apr 7, 2018

Thanks!

@alopatindev

This comment has been minimized.

Copy link

commented Sep 2, 2018

Is there something similar to %x[...] in standard library to handle paths with weird characters?

$ mkdir -p "path/with spaces, \"quotes\" and 'apostrophes'/"
$ irb
irb(main):001:0> path = "path/with spaces, \"quotes\" and 'apostrophes'/"
=> "path/with spaces, \"quotes\" and 'apostrophes'/"
irb(main):002:0> %x[ls #{path}]
ls: cannot access 'path/with': No such file or directory
ls: cannot access 'spaces,': No such file or directory
ls: cannot access 'quotes': No such file or directory
ls: cannot access 'and': No such file or directory
ls: cannot access 'apostrophes/': No such file or directory
=> ""
irb(main):003:0> %x[ls '#{path}']
ls: cannot access 'path/with spaces, "quotes" and apostrophes/': No such file or directory
=> ""
@lukas2

This comment has been minimized.

Copy link

commented Jan 24, 2019

Useful thanks!

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.