To run a ruby program we use the command ruby

ruby program_name.rb.

Ruby being an interpreter style language, each line is interpreted(read) one after the other and executable object code file is created for reuse like in case of compiler languages C, C++, etc.. To run a ruby code you need a ruby interpreter installed in your system.

Linux (all UNIX like operating systems) has a way of executing a file that can help make a script self executable (that is making a ruby script ruby by just calling its name, with no need to specify the interpreter program). Its called #!. Dennis Ritchie, who introduced it, referred it as hash-bang though over the course of time it came be known by many names such as shebang/hashbang/pound-bang/hash-exclam/hash-pling.

This #! character are never used alone, it is followed by the location of the interpreter program using which you want to run that particular file (script).

Now to make our ruby script executable we need to add to the first line the following statement

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#!/usr/bin/ruby

puts "The ruby code, starts from line 2" How does this work?

A program is executed using a tool known as program loader. In linux when a program loader loads the file for execution and sees that there is #! notation in the first line, it would understand that this program needs to be passed to an interpreter program for execution. In case our ruby script when it gets executed ( $./program_name.rb) the program loader would pass it on to the ruby interpreter program that is defined in the hash-bang line as /usr/bin/ruby.

Thus the program loader would pass the file name and path to the ruby interpreter, in short the command $ruby program_name.rb ( $/usr/bin/ruby program_name.rb) would be execute.

Since the hash-bang line starts with hash ruby interpreter would consider it as a command line only.

The last and Final STEP ( IMPORTANT )

In Linux and any other UNIX like operating system no system can execute unless it is given the permission to execute. So we use the command chmod to give the permission to execute.

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$chmod 755 program_name.rb

Following these steps you can make a ruby scrip executable.

Note :- The above mentioned method is not for ruby alone, any script can be made self executable using the above mentioned steps. We just have to change the program that is suppose to execute the program .

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#!/bin/sh

#!/bin/csh

#!/usr/bin/perl -T

#!/usr/bin/php

#!/usr/bin/python -O

#!/usr/bin/ruby

Also the above mentioned is the location of the interpreter program if its in a different location then you will have to use that location or could use env – environment variable in linux thus the hash-bang statement changes to

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#!/usr/bin/env ruby

That is the interpreter is searched among the environment variable, thus during run time the appropriate interpreter would be searched and used. For more details see the env wikipedia page

Happy Coding.