Why don't I get any syntax errors when I execute my Python script with Perl?

Question

I just wrote some testing python code into test.py, and I'm launching it as follows:

perl test.py

After a while I realized my mistake. I say "after a while", because the Python code gets actually correctly executed, as if in Python interpreter!

Why is my Perl interpreting my Python? test.py looks like this:

#!/usr/bin/python

...Python code here...

Interestingly, if I do the opposite (i.e. call python something.pl) I get a good deal of syntax errors.

I'm guessing it's because of the #! in the beginning of the file. Indeed if I remove the she-bang, I'm getting the expected behavior. Isn't that a bad idea from the security perspective, anyway? — Dacav
– Dacav, Commented Apr 10, 2015 at 14:20
No. The point of the shebang path it to specify an interpreter. If you don't trust the code to run, then you shouldn't be running it in the first place. — Sobrique
– Sobrique, Commented Apr 10, 2015 at 14:21
No, not really. Your script is a text file. No more, no less. It won't 'run' without an interpreter. — Sobrique
– Sobrique, Commented Apr 10, 2015 at 14:23
"Why is my Perl interpreting my Python?" is not "a problem that can no longer be reproduced or a simple typographical error." Voted to reopen. The upvotes on the Q and the A show this is a question of popular interest. — ikegami
– ikegami, Commented Apr 10, 2015 at 20:28
@ikegami Regardless of popularity, this is clearly not "a simple typographical error...resolved in a manner unlikely to help future readers." Voted to reopen. — ThisSuitIsBlackNot
– ThisSuitIsBlackNot, Commented Apr 10, 2015 at 20:37

ikegami · Accepted Answer · 2018-02-28 18:13:19Z

114

From perlrun,

If the #! line does not contain the word "perl" nor the word "indir" the program named after the #! is executed instead of the Perl interpreter. This is slightly bizarre, but it helps people on machines that don't do #! , because they can tell a program that their SHELL is /usr/bin/perl, and Perl will then dispatch the program to the correct interpreter for them.

For example,

$ cat a
#!/bin/cat
meow

$ perl a
#!/bin/cat
meow

edited Feb 28, 2018 at 18:13

answered Apr 10, 2015 at 14:25

ikegami

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8 Comments

cjm Over a year ago

Wow. Talk about your obscure features. I've been using Perl for more than 20 years, and I had no idea it did that.

tjd Over a year ago

I started using Perl v4 on DOS, VMS & Solaris. It's OS agnostic/bridging features like this that made cross platform life so much easier.

zxq9 Over a year ago

@MarcvanLeeuwen When you write programs for Linux, OSX, VAX/VMS, Windows, Solaris, OS/2, and whatever else the most annoying part of porting a script-language program is getting it started, as many of these systems, though usually sharing the "type a command, have it found & executed" feature in common, do nearly everything else differently. This Perl feature makes Perl an easy gap-bridge in functionality -- you can write just a Unix-style shebang and if Perl is present the code, whether Perl code or not, will always work -- its like a more universal #! /usr/bin/env foo.

Barmar Over a year ago

This just cements Perl's reputation as the kitchen sink of programming languages. As an interesting observation, I believe the original implementation of shebang was as a shell feature, it only moved into the Unix kernel later. Perl includes many shell mechanism (e.g. backticks for substituting command output), this is just one more.

Vadim Pushtaev Over a year ago

ruby does the same >.<

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