CODEWITHSUNDEEP
pythonpython-3.x
Igor
Igor

Reputation: 6285

Check for python3 presence inside the script

In python the first line of the script should be

#!/usr/bin/env/python{3}

Is there a way to do:

if python:
    #!/usr/bin/env/python
else:
    #!/usr/bin/env/python3

EDIT:

Running python in RHEL7 bring up python-2.7.5 (default).

Only running python3 will execute python3-3.6.8 on my RHEL7.

Upvotes: 1

Views: 200

Answers (2)

tripleee
tripleee

Reputation: 189913

None of those are correct. The correct command is /usr/bin/env and the argument to that, after a space, is the name of the actual interpreter you want it to look up.

Your question is a bit of a "turtles all the way down" problem. You have to know what command you want to run. You could of course create yet another tool and call it something like py3orpy but then you need to know that that exists in the PATH before you try to ask env to find it.

I would expect us to eventually converge on python; if you can't rely on that, perhaps the least error-prone solution is to figure out what's correct for the target system at installation time, and have the installer write a correct shebang. Or just install a symlink /usr/local/bin/python3 if it doesn't exist already, and hardcode #!/usr/bin/env python3 everywhere.

Upvotes: 1

Macattack
Macattack

Reputation: 1990

I can't say I recommend this at all, but it does work:

#!/bin/bash

_=""""
if [[ -x '/usr/bin/python3' ]]
then
    exec /usr/bin/python3 "$0" "$@"
elif [[ -x '/usr/bin/python' ]]
then
    exec /usr/bin/python "$0" "$@"
else
    echo "No python available"
    exit 1
fi
"""

import sys
sys.stdout.write("you made it\n")

Can't do from __future__ import print_function because it has to be the first line of python.

Principles here are to use bash to do the executable detection but also make it valid python so you can just re-execute with the python interpreter on the same file.

Upvotes: 1

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