Vim & Vision

[ #138 ] Please use /usr/bin/env Permalink

Shell Added ...oh I don't know?

For your scripts/programs, instead of:

#!/usr/bin/python
#!/usr/bin/perl
#!/usr/bin/ruby
#!/bin/bash

use env instead. How?

#!/usr/bin/env perl
#!/usr/bin/env python
#!/usr/bin/env ruby
#!/usr/bin/env bash

What does env do?

It finds the executable for you, in your path.

Why should you?

Because almost every system (except apparently certain versions of Unicos and Openserver) has the env program in /usr/bin/, but the perl or python or ruby or bash executable is more often found in a different directory than /usr/bin/.

Really? Where else could they be?

I've seen them in:

/usr/local/bin
/opt/local/bin
/usr/pkg/bin

...etc. They could be installed anywhere actually. Perhaps even your home directory. /usr/bin/env solves this portability problem when you try to run a script on a machine with different location for perl/python/ruby/bash etc.

But on my system, env is in /bin/ not /usr/bin

No it isn't. Look in /usr/bin/ too - I'll bet you find it. If you really don't, then you are using a pretty strange system (perhaps Unicos or something) - in which you might have many greater portability problems than this.

Is there any sitution where I should NOT use /usr/bin/env?

Yeah there could be. Let's say you have multiple versions of perl installed on your system - 5.8 and 5.6, where the main perl in your path points to 5.8. You could have a script that purposely needs to use 5.6 instead of 5.8 because of certain compatibility problems. In this case you might want to use #!/full/path/to/perl5.6 not #!/usr/bin/env.