What should I use for a Perl script's shebang line?

perl shebang
Anonymous picture Anonymous · May 8, 2010 · Viewed 49.9k times · Source

Which of these is better or faster to use as the shebang line for a Perl script?

#! perl

#! perl.exe

#! fullpath/perl(/perl.exe)

#! partialpath/perl(/perl.exe)

And, when using #!perl, when it works on a particular system, how do I find out in the script which perl interpreter I'm using so I can put that one into the shebang line?

And, if using a /path/path/perl, are * or ... allowed to be used for the folders?

Answer

Schwern picture Schwern · May 8, 2010

If you have to hard code #!, use #!/usr/bin/env perl. Why? What you want is for the Perl program to run with the user's preferred Perl. That's going to be the first on in their PATH. #!perl doesn't do what I mean, it doesn't search the user's PATH, #!/usr/bin/env perl is how you pull that off. /usr/bin/env will always be there on Unix systems.

If the user is using Windows, as others have pointed out, it doesn't matter. Windows doesn't use #! it uses file extension associations. Make sure your program is called foo.pl or something and it'll work. But include the #! line anyway as some utilities and editors make use of it.

If you're shipping code, let the installer take care of it. Both MakeMaker/Makefile.PL and Module::Build/Build.PL will change your #! line to match the perl the user used to install with. They will take care of this problem for you.

If you are installing code for your own production use, you should use the full path to a particular copy of perl. Which copy of perl? One specific to your project. Does this mean you need to compile perl for every project? No, you can make a symlink. Project foo might have /usr/local/bin/fooperl point at /usr/bin/perl5.18. Use #!/usr/local/bin/fooperl. Now if you decide to upgrade perl you can do it per project by changing the symlink.

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