chorankates has asked for the wisdom of the Perl Monks concerning the following question:

i'm trying to use variables in #line directives so that i can pass the proper line/file on. essentially, i've written a wrapper to Test::More, and instead of seeing which line/file the tests fail on, it displays the line in my wrapper library.

short version of what i'm trying:
test.pl 
#!/usr/bin/perl -w

use strict;
use warnings;

use lib '.';
use test;

my $l = 200;
my $ld = 'foo';

#line $l $ld ;
test::test();

exit;

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test.pm 
package test;
use strict;
use warnings;

require Exporter;
our @ISA = qw(Exporter);
our @EXPORT_OK = qw();

sub test {    
    my @caller = caller();
    
    print "@caller\n";
    
    print "DBGZ" if 0;
    
}

1;

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i'm seeing: 
$ perl test.pl
main test.pl 13

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i want to see: 
$ perl test.pl
main foo 200

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the llama book says: Technically, it matches the pattern /^#\s*line\s+(\d+)\s*(?:\s"(^"+)")?\s*$/, with $1 providing the line number for the next line, and $2 providing the optional filename specified within quotes. (A null filename leaves __FILE__ unchanged.)

making me think this is not possible, but then i see AutoSplit.pm: 

#line $lineno "$filename (autosplit into $path)"

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can anyone point me in the right direction to allow variables in #line directives? or at least confirm that it is not possible..

Replies are listed 'Best First'.
Re: variable based #line directives?
by Corion (Patriarch) on Aug 20, 2011 at 20:46 UTC

    I think you can do the appropriate faking of #line numbers only through eval. #line directives are only evaluated at compile time of code, so they cannot use variables.

    If you want to wrap/warp Test::More, you want to look at Test::Builder. It also tells you how to skip levels in reporting the error location - see caller.

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[d/l]
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      thanks very much for suggesting i look at Test::Builder, was able to modify Test::Builder::Level in my wrapping module and i am now getting the correct line/script number.

      just for my edification, can you point me in the direction of some eval #line directive examples? all of the formats i tried before going to Test::Builder did not affect caller() at all. i tried (same code as originally posted, but adding this on line 13 of test.pl):

      • eval "#line $l $ld";
      • eval("#line $l $ld");
      • eval qq{#line $l $ld} or die $!;
      when i tried the last one, i got 'bad file descriptor', which i don't understand either..
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        The #line directive takes hold only for the code compiled within the eval string. So you can only "set" the line number by doing

        my $code = <<CODE;
#line 200
die "Hello world";
CODE

eval $code;
warn $@;

__END__
Hello world at (eval 1) line 200.

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        i got 'bad file descriptor', which i don't understand
        eval returns the value of the last evaluated expression. In your case, there is no expression, so eval returns undef, which triggers die. Use something like
        eval qq{#line $l $ld\n1;} or die "$!";

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        $@ is more common (and meaningful) after eval than $! (see perlvar).
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Re: variable based #line directives?
by chromatic (Archbishop) on Aug 21, 2011 at 08:24 UTC
    ... or at least confirm that it is not possible..

    It is not possible to use a variable in a #line directive. See S_incline() in toke.c; the function returns unless the first token after the #line directive contains only digits.

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      exactly what i needed to stop my unending codesearch.google.com searches, thanks!
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Re: variable based #line directives?
by TomDLux (Vicar) on Aug 20, 2011 at 23:00 UTC

    If you have #line 200 foo, it works.

    As Occam said: Entia non sunt multiplicanda praeter necessitatem.

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[d/l]
      right, but i want to use variables in my #line directive. the literal version you show works fine, but is not what i am looking for here
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