make #!/usr/bin/env python -u shebang portable

Question

I have this non-portable shebang:

#!/usr/bin/env python -u

It is non portable because python -u is fed as one single arg to env on my system.

Challenge: make this shebang portable changing the shebang only - that is to say a one-liner.

In other words, no solutions

from the question Disable output buffering
from the question Cannot pass an argument to python with "#!/usr/bin/env python"

I asked for a solution involving the shebang line only, not a multi-line solution. — dnozay, Oct 11 '13 at 04:45

user4815162342 · Answer 1 · 2016-03-18T20:57:53.713

11

I'd use the following:

#!/bin/sh
"""true"
exec python -u "$0" "$@"
"""
# python code goes here

The line """true" will be parsed by sh as true, because it consists of an empty "" string followed by "true". Since true is a no-op command, it will be effectively ignored, and the following line will execute the Python interpreter.

On the other hand, Python will parse the """true" line very differently, as the opening of a triple-quoted string which starts with true" and is closed two lines below. Since the string is not used for anything, the Python interpreter will effectively ignore the shell snippet that starts up Python. It is the difference in interpretation of """xxx" that allows Python and sh code coexist in the same script.

For a simple test, append something like:

import sys
print "hello!", sys.argv

Given a reasonable sh implementation (and taking into account the time to start Python), this should not be measurably slower than using env.

edited Mar 18 '16 at 20:57

answered Oct 10 '13 at 19:15

user4815162342

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+1 That's dirty, but somehow satisfying – Oct 10 '13 at 19:37
One drawback is that the hack will be treated as part of (if not the entirety) of the script's docstring. – chepner Oct 10 '13 at 20:08
@chepner Is this a problem in practice? Docstrings of importable modules are quite useful, but I can't think of a use for docstrings in executable scripts. – user4815162342 Oct 10 '13 at 20:11
`pydoc` displays the contents of the module docstring as the description of the script. – chepner Oct 10 '13 at 20:16
Couldn't you continue to add to the end of the docstring? – Mark Ransom Oct 10 '13 at 20:25
There was a similar trick with tcl (playing games with commenting rules) – SheetJS Oct 11 '13 at 05:14

make #!/usr/bin/env python -u shebang portable

1 Answers1