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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

awesome summary - thanks!

@JosephPecoraro
@sivakumar-kailasam

Liked the extra advice :)

@devilankur18

Just Awsesome

@marksliva

Thank you!

@cizixs

Very useful , Thx!

@NeWbLt123

Thanks, very helpful !

@mx4492

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

@chrishough

thanks man!

@barbolo

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

@yanbit

thanks man!

@kassane

Awesome man!

@dminca

Thanks man, very interesting and useful :+1:

@mika-cn

Awesome man! thanks

@mkowaliszyn

@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

@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")
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