Gheek.net

February 28, 2011

Howto Make Script More Portable With #!/usr/bin/env As a Shebang

Filed under: expect, linux, nix, perl, php, shell scripts — lancevermilion @ 9:33 am

The following article is taken directly from http://www.cyberciti.biz/tips/finding-bash-perl-python-portably-using-env.html by VIVEK GITE.

You may have noticed that most shell and perl script starts with the following line:
#!/bin/bash
OR
#!/usr/bin/perl

It is called a shebang. It consists of a number sign and an exclamation point character (#!), followed by the full path to the interpreter such as /bin/bash. All scripts under UNIX and Linux execute using the interpreter specified on a first line.

However there is a small problem. BASH or Perl is not always in the same location (read as PATH) such as /bin/bash or /usr/bin/perl. If you want to make sure that script is portable across different UNIX like operating system you need to use /usr/bin/env command.

env command allows to run a program in a modified environment.

Find line
#!/bin/bash

Replace with
#!/usr/bin/env bash

For example here is a small script:

#!/usr/bin/env bash
x=5
y=10
echo "$x and $y"

OR

#!/usr/bin/env perl
use warnings;
print "Hello " x 5;
print "\\n";

Now you don’t have to search for a program via the PATH environment variable. This makes the script more portable. Also note that it is not foolproof method. Always make sure you have /usr/bin/env exists or use a softlink/symbolic link to point it to correct path. And yes your work (script) looks more professional with this hack 🙂

Advertisements

Leave a Comment »

No comments yet.

RSS feed for comments on this post. TrackBack URI

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

Blog at WordPress.com.

%d bloggers like this: