ruby

TLDR

Start an interactive Ruby session (IRB)

$ ruby

Execute a Ruby script

$ ruby [script.rb]

Execute Ruby code from command line

$ ruby -e "[puts 'Hello, World!']"

Check syntax without executing

$ ruby -c [script.rb]

Run with warnings enabled

$ ruby -w [script.rb]

Execute and print result of expression

$ ruby -e "p [1, 2, 3].sum"

Process input line by line

$ ruby -n -e "puts $_.upcase" [file.txt]

In-place edit a file

$ ruby -i -pe "gsub(/old/, 'new')" [file.txt]

SYNOPSIS

ruby [options] [-e command] [programfile] [arguments]

ruby is the interpreter for the Ruby programming language. It executes Ruby scripts or runs interactive sessions, providing a dynamic, object-oriented environment for general-purpose programming.
Ruby emphasizes programmer happiness and productivity with elegant syntax. Everything is an object, and the language supports multiple programming paradigms: object-oriented, functional, and imperative.
The -e option allows quick one-liners without creating a file. Combined with -n or -p, Ruby becomes a powerful text processing tool similar to awk or perl.
For interactive exploration, use irb (Interactive Ruby) or pry for enhanced REPL features.

PARAMETERS

-e command

Execute command as one line of script

-c

Check syntax only, don't execute

-w

Enable warnings

-W level

Set warning level (0=silent, 1=medium, 2=verbose)

-d, --debug

Enable debug mode

-v, --verbose

Print version and enable verbose mode

--version

Print version and exit

-n

Wrap script in while gets() ... end loop

-p

Like -n but print $_ after each iteration

-a

Auto-split mode (with -n or -p), sets $F

-i [ext]

In-place edit mode (backup with extension if given)

-I dir

Add directory to load path

-r library

Require library before executing

-S

Search for script in PATH

-x [dir]

Extract script from message and change to dir

CAVEATS

Ruby versions can differ significantly. Use version managers like rbenv or rvm to manage multiple Ruby installations.
Gem dependencies should be managed with Bundler. Run scripts with bundle exec to ensure correct gem versions.
Ruby's global interpreter lock (GIL/GVL) limits true parallelism in threads. Use processes or specialized libraries for CPU-bound parallelism.

HISTORY

Ruby was created by Yukihiro "Matz" Matsumoto in Japan, with the first public release in 1995. Matz designed Ruby to be more powerful than Perl and more object-oriented than Python. Ruby gained worldwide popularity with the Ruby on Rails web framework released in 2004.