Re^2: How do I use 'which' in the hash-bang line?

[davies]

Note that env does not allow the passing of parameters to the target, so that #!/usr/bin/env perl -w does not work. At least, this was true the last time I tried.

Regards,

John Davies

[haukex]

<update2> Sorry, I got so caught up in the point I was trying to make - that Perl scans the shebang line even when running the script as perl test.pl - that I missed the limitation that the AM pointed out below, that you are right that #!/usr/bin/env perl -w does in fact not work when invoking the script via ./test.pl. </update2>

so that #!/usr/bin/env perl -w does not work

It does for me:

$ cat test.pl 
#!/usr/bin/env perl -wls
print $x+undef;
$ perl test.pl -x=5
Use of uninitialized value in addition (+) at test.pl line 2.
5

From perlrun: 'The #! line is always examined for switches as the line is being parsed. ... Parsing of the #! switches starts wherever "perl" is mentioned in the line.'

(I'm not sure about the history of this feature at the moment.) Update: The description of this feature was in perl-5.000, although apparently the support for which options are supported there has changed, for example perl58delta says "The command-line options -s and -F are now recognized on the shebang (#!) line." or perl5100delta says "The -C option can no longer be used on the #! line." (Although as choroba pointed out and as the docs say: "It wasn't working there anyway, since the standard streams are already set up at this point in the execution of the perl interpreter.")

[Anonymous Monk]

Try:

$ chmod a+x test.pl
$ ./test.pl

The env utility *supports* passing arguments to the command .... if invoked from command line (with args split by shell). As part of shebang, however, all following arguments are passed to env as a single string. So if you don't have a command such as "perl -wls" on the $PATH, the result is a failure.

[haukex]

As part of shebang, however, all following arguments are passed to env as a single string.

That's a very good point, I've edited my post, thanks.