Filename expansion with `=` in ZSH

I do this somewhat often to find where a binary exists in my $PATH. For a script in my path, I might also do something like this to quickly edit it.

$ echo `which ls`
$ vi `which myscript.py`

The other day, I learned about a handy little shortcut ZSH provides:

$ echo =ls
/bin/ls

$ what =ls
/bin/ls:
        PROGRAM:ls  PROJECT:file_cmds-479
         Copyright (c) 1989, 1993, 1994
        PROGRAM:ls  PROJECT:file_cmds-479
         Copyright (c) 1989, 1993, 1994

From the “Filename Expansion” section of zshexpn(1):

= expansion

If a word begins with an unquoted `=’ and the EQUALS option is set, the remainder of the word is taken as the name of a command. If a command exists by that name, the word is replaced by the full pathname of the command.

This doesn’t work in sh(1) or bash(1); it’s a ZSH thing. The EQUALS option is set by default.

EQUALS <Z>

Perform = filename expansion. (See the section ‘Filename Expansion’.)