Using the shebang

Using the shebang
Learn what the shebang is and how to use it to ensure your script files run correctly.

This article explains the purpose of the shebang and how to use it to make scripts execute properly.

What is the shebang?
The shebang is a special character sequence at the beginning of a script file that tells the system which program should execute the script. It always appears on the first line and consists of #! followed by the path to the interpreter. You can also include command-line options if needed.

For example, the following line specifies the Perl interpreter and the -w option:

#!/usr/bin/perl -w

The shebang is especially important for CGI scripts. For instance, a file named script.cgi with this shebang can be executed from the command line like this:

./script.cgi

The Apache web server can also run the file as a CGI script because it knows to call the Perl interpreter.

Note

Many scripting languages, such as Perl, use # for comments. The shebang is a special exception to this rule.

Using the correct shebang
Here are recommended shebangs for scripts running on ruachost.com servers:

Language	Shebang
Perl	#!/usr/bin/perl
Python (generic)	#!/usr/bin/python
Python (specific version)	#!/usr/bin/python2.7 #!/usr/bin/python3.6 …
Ruby	#!/usr/bin/ruby
PHP	#!/usr/local/bin/php

Note

For PHP scripts that generate web output, the shebang is not required.

You can also make scripts more portable by using env to locate the interpreter dynamically:

#!/usr/bin/env ruby

This finds the Ruby interpreter whether it is in /usr/bin/, /usr/local/bin/, or elsewhere, so you don’t need to know the absolute path.

More information
For further details about the shebang, visit Wikipedia: Shebang (Unix).