Fedora ponders the Python 2 end game

POSIX created the getconf(1) utility just so you could do PATH="$(getconf PATH)" to get the default system provided PATH guaranteed to provide the POSIX utilities. It's one of the rare instances where they didn't just codify existing practice. Perhaps for that reason it's an underused and virtually unknown command. Theoretically Linux distributions could extend it so that something like getconf PYTHON2 prints the default python2 interpreter (if available). That doesn't by itself solve the problem of a simple shebang line, but I think it's the least distributions could do to meet developers half-way.[1]

For Lua scripts I often abuse a coincidence of shell and Lua syntax so I can do

 #!/bin/sh
_=[[
  # shell script code to locate a Lua interpreter
]]
-- Lua code

where _=[[ begins a multiline string in Lua but is a harmless assignment in shell. Because the semantics of shell syntax effectively require parsing the file line-by-line, the shell code never reaches the terminating ]] or subsequent Lua code as long as you invoke exec or exit before reaching ]]. I'm not familiar with Python syntax but perhaps something similar can be done.

[1] Distributions could standardize on the "python2" command name, but you still run into the problem of a bad PATH variable. Ideally you'd be able to do something like #!/usr/bin/env command -p python2, where the -p switch to the command utility only searches the default PATH from getconf PATH. And where env(1) locates command(1), as command(1) is usually a built-in and even when it's available as an independent utility I don't know if you can expect it to be in /bin or /usr/bin--not in the same way that env(1) is reliably at the absolute path /usr/bin/env. But Linux is one of the few Unix systems that concatenate all the shebang command argument words before invoking the interpreter, so the above will work on macOS and some other kernels, but not on Linux.