http://www.perlmonks.org?node_id=1101668


in reply to Re: Turning on regexp debugging at runtime
in thread Turning on regexp debugging at runtime

As for easily turning debugging on and off, here's one way via environment vars:

my $re1 = qr/foo|bar/;
{
    use if $ENV{DEBUG_REGEX}, qw/re Debug EXECUTE/;
    my $re2 = qr/quz|baz/;
    print "xfoox"=~$re1, "ybazy"=~$re2;
}

[download]

gives you run-time debug info on $re2 only when the environment var DEBUG_REGEX is set.

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Re^3: Turning on regexp debugging at runtime
by SBECK (Chaplain) on Sep 23, 2014 at 16:15 UTC

    Thanks for both of these replies, especially the second since I wasn't aware of the DEBUG_REGEX environment variable.

    I should have been a bit clearer, but it appears that what I want to do probably can't be done. For example, say I have the absurdly simple script: 

    $re1 = qr/a/;
$re2 = qr/b/;
$re3 = qr/c/;
$str = "ab";

$str =~ $re1;
$str =~ $re2;
$str =~ $re3;

    [download]

    what I want to do is step through the code (in the debugger) and turn on debugging (by executing "use re 'debug'") when I match against $re2 but then turn it back off before proceeding to the $re3 match.

    I could put each in it's own scope, but that would be messy (I don't really want to put every regexp in it's own scope so that I could potentially debug it individually).

    Even worse is that the regexps in question were built outside of the scope, so I actually end up with something more similar to this: 

    $str = "abc";
$re1 = qr/a/;
$re2 = qr/b/;
{
   use re 'debug';
   $str =~ $re1;
   {
      no re 'debug';
      $str =~ $re2;
   }
}

    [download]

    which won't print any debugging info at all.

    Oh well, I can do what I've always done (temporarily enable debugging and then go to the point in the code I'm interested in ignoring all the unwanted debugging output).

[reply]
[d/l]
[select]

      The name DEBUG_REGEX is made up, and can be anything (note the test of $ENV{DEBUG_REGEX} in the code).

      How about:

      my $re1 = qr/a/;
my $re2 = do { use if $ENV{FOO_DEBUG_REGEX},
    qw/re Debug EXECUTE/; qr/b/ };
my $re3 = qr/c/;
my $str = "ab";
$str =~ $re1;
$str =~ $re2;
$str =~ $re3;

      [download]

      will output run-time debug info on $re2 only when the environment var FOO_DEBUG_REGEX is set.

      I'm not sure if this can be done dynamically in the debugger, perhaps another monk with more experience there can help. The documentation does say that use re 'debug'; has both compile-time and run-time effects.

[reply]
[d/l]
[select]

        Thanks. I misunderstood DEBUG_REGEX.

        Unfortunately, the actual situation is very complicated. There are literally hundreds of regexps, and I'd like to be able to debug any one of them at any time. Also, they are called multiple times, so I might only be interested in the 4th time that a regexp is called.

        Unfortunately, the "use regexp" pragma is applied when the regexp is created... I want something to turn debugging on when a regexp is matched against.

        It's really not that big of a deal... I can workaround it by simply ignoring a lot of unwanted output. I was just hoping for something a little cleaner during debugging time.

[reply]
      Hello

      Are you aware you can scope more easily using

      $str = "abc";
$re1 = qr/a/;
$re2 = qr/b/;
{
   use re 'debug';
   $str =~ $re1;
}
$str =~ $re2;

      [download]
      However since the whole process does not seem to help you anyway: Can you please provide more code? It doesn't seem very useful to match like crazy but not doing anything with the match results.
[reply]
[d/l]

        Your example doesn't work. The re pragma (as far as I can tell) does something when the regexp is created, so if I run your code, nothing is output.

        However, even if it was, this really doesn't do what I want. Imagine the following code: 

        $re1 = qr/.../;
$re2 = qr/.../;
...
$reN = qr/.../;

@str = ('some','list','of','strings');

foreach my $str (@str) {
   $str =~ /$re1/;
   $str =~ /$re2/;
   ...
   $str =~ /$reN/;
}

        [download]

        That's basically the situation that I have. But I don't want to turn on debugging for all regexps, or even for a single regexp every time it is used. What I want is to be able to debug $re2 when applied to the 5th string and nothing else.

        The way I want this to work is that I run this program in the debugger, step through until I get to the particular regexp match that I want to debug, and then I type "use re 'debug'" and I'm ready to go.

        Unfortunately, it doesn't work. The regexp was already created without debugging turned on, so (as far as I can tell), there is no way to turn it on for this one particular match.

        Anyway, as I said, it's far from the end of the world... I can turn on debugging and then run the script to the point i'm interested in and ignore all the unwanted debug output from all the other times the regexp was matched. This is mainly a convenience question.

[reply]
[d/l]

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