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 by VIVEK GITE.

You may have noticed that most shell and perl script starts with the following line:

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

Replace with
#!/usr/bin/env bash

For example here is a small script:

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


#!/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 🙂

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