Re^2: Can I write a transparent shell wrapper to start the correct build of Perl?

There's a potential subtle problem with using env, which is that you typically can't pass arguments to the perl binary this way, like for example

#!/usr/bin/env perl -w
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On my Debian Linux this produces

$ ./666330.pl
/usr/bin/env: perl -w: No such file or directory
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This is not a problem with env (running /usr/bin/env perl -w 666330.pl from the command line would work fine...), but rather with many Unix kernels, which treat everything after the interpreter specified on the shebang line (here /usr/bin/env) as a single argument, i.e. it would pass "perl -w" to /usr/bin/env as the program name to execute... which of course doesn't exist. This can easily be seen with strace:

$ strace -e trace=execve ./666330.pl
execve("./666330.pl", ["./666330.pl"], [/* 24 vars */]) = 0
execve("/home/almut/bin/perl -w", ["perl -w", "./666330.pl"], [/* 24 v
+ars */]) = -1 ENOENT (No such file or directory)
execve("/usr/local/bin/perl -w", ["perl -w", "./666330.pl"], [/* 24 va
+rs */]) = -1 ENOENT (No such file or directory)
execve("/usr/bin/perl -w", ["perl -w", "./666330.pl"], [/* 24 vars */]
+) = -1 ENOENT (No such file or directory)
execve("/bin/perl -w", ["perl -w", "./666330.pl"], [/* 24 vars */]) = 
+-1 ENOENT (No such file or directory)
execve("/usr/bin/X11/perl -w", ["perl -w", "./666330.pl"], [/* 24 vars
+ */]) = -1 ENOENT (No such file or directory)
/usr/bin/env: perl -w: No such file or directory
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Re: Can I write a transparent shell wrapper to start the correct build of Perl? by Anonymous Monk on Jun 25, 2008 at 17:02 UTC
I fixed builds that attempted to use the -w option when calling perl. The shell was treating it as a single command name rather than a command with a switch. The easy way to fix this would be to do something similar to: ln -s ./perl 'perl -w' This will create a symbolic link named 'perl -w' allowing the build to work, in my case. I was running into this with trying to compile the library pango and it was annoying me, because I couldn't figure out where env was calling for the file 'perl -w' to change it. The -w switch only enables some additional warnings, so not entirely necessary. Another option might be to create a script named 'perl -w' then have it call perl with the -w switch.	[reply]

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Re: Can I write a transparent shell wrapper to start the correct build of Perl?
by Anonymous Monk on Jun 25, 2008 at 17:02 UTC

I fixed builds that attempted to use the -w option when calling perl. The shell was treating it as a single command name rather than a command with a switch. The easy way to fix this would be to do something similar to: ln -s ./perl 'perl -w' This will create a symbolic link named 'perl -w' allowing the build to work, in my case. I was running into this with trying to compile the library pango and it was annoying me, because I couldn't figure out where env was calling for the file 'perl -w' to change it. The -w switch only enables some additional warnings, so not entirely necessary. Another option might be to create a script named 'perl -w' then have it call perl with the -w switch.

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