Why do people write #!/usr/bin/env python on the first line of a Python script?

Question

It seems to me like the files run the same without that line.

Answer 1

This is meant as more of historical information than a "real" answer.

Remember that back in the day you had LOTS of unix like operating systems whose designers all had their own notion of where to put stuff, and sometimes didn't include Python, Perl, Bash, or lots of other GNU/Open Source stuff at all.

This was even true of different Linux distributions. On Linux--pre-FHS[1]-you might have python in /usr/bin/ or /usr/local/bin/. Or it might not have been installed, so you built your own and put it in ~/bin

Solaris was the worst I ever worked on, partially as the transition from Berkeley Unix to System V. You could wind up with stuff in /usr/, /usr/local/, /usr/ucb, /opt/ etc. This could make for some really long paths. I have memories of the stuff from Sunfreeware.com installing each package in it's own directory, but I can't recall if it symlinked the binaries into /usr/bin or not.

Oh, and sometimes /usr/bin was on an NFS server[2].

So the env utility was developed to work around this.

Then you could write #!/bin/env interpreter and as long as the path was proper things had a reasonable chance of running. Of course, reasonable meant (for Python and Perl) that you had also set the appropriate environmental variables. For bash/ksh/zsh it just worked.

This was important because people were passing around shell scripts (like perl and python) and if you'd hard coded /usr/bin/python on your Red Hat Linux workstation it was going to break bad on a SGI...well, no, I think IRIX put python in the right spot. But on a Sparc station it might not run at all.

I miss my sparc station. But not a lot. Ok, now you've got me trolling around on E-Bay. Bastages.

[1] File-system Hierarchy Standard. https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard

[2] Yes, and sometimes people still do stuff like that. And no, I did not wear either a turnip OR an onion on my belt.