Can't find mkvirtualenv, but can execute it

Question

I'm trying to run mkvirtualenv from a bash script, and I'm keep being told that it can't be found - yet it seems that my system can't make up it's mind about whether or not it can find it. Can anyone explain why I can execute it from the terminal, but not from a script?

jimbo@wavefront:~$ locate mkvirtualenv
jimbo@wavefront:~$ which mkvirtualenv
jimbo@wavefront:~$ mkvirtualenv --version
13.1.2
jimbo@wavefront:~$

Answer 1

It's because it's a function attached to the shell. Run this to see it:

$ type mkvirtualenv

Answer 2

Avoid using which to check for binaries/etc. It isn't standardized, isn't always available and is an external binary itself (and so is more expensive than the better choices).

The better choices are type and command .

They are both built-ins, both standardized (at least at their most basic levels) and, because they are built-in, can see shell functions and aliases too.