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Ovid (2709)

Ovid
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Stuff with the Perl Foundation. A couple of patches in the Perl core. A few CPAN modules. That about sums it up.

Journal of Ovid (2709)

Tuesday December 08, 2009
09:02 AM

Regex Captures in Debugger

[ #39990 ]

Stumbled across this weird behavior today. Took a while to debug it. In the debugger, I'm not seeing the "dollar digit" regex capture variables set, even though the regex matches.

$ perl -de 1

Loading DB routines from perl5db.pl version 1.3
Editor support available.

Enter h or `h h' for help, or `man perldebug' for more help.

main::(-e:1):   1
  DB<1> ($foo) = ('abcd' =~ /(bc)/)

  DB<2> x $1
0  undef
  DB<3> x $foo
0  'bc'

Is this documented? I can't find it.

Update: Rafael explained it. The digit variables are lexically scoped. That's why you can assign to a package variable in a debugger, but not a lexical.

  DB<6>  'abcd' =~ /(bc)/ && print $1
bc

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  • I think this is the same way that the debugger doesn't see lexicals declared on the previous line;

    eg:
          DB my $foo = 'bar';
          DB x $foo
          0 undef

    So this works:

          DB ($foo) = ('abcd' =~ /(bc)/) && print $1

    • Yeah, Rafael pointed that out to me and I updated my post before I saw your response.

      By the way, you can use <ecode>some code here</ecode> tags to make your post prettier :)