Backreferencing Question

[zyphon08]

I'm fairly new to Perl (I know other languages), but I am extremely new to regular expressions. While writing a script, I ran into a little problem while trying to backreference to a match in a regular expression. The part of the code was similar to the following:

if(/(hello)/)
{
$foo = $1;
if(/(blah)/)
{
$bar = $1;
}
}

print "$foo and $bar";

What I thought before I ran into this problem was that the output would look like..

hello and blah

But I found out that the output is actually (assuming that my problem isn't due to some logical error that I've yet to notice)..

blah and blah

I don't really understand why this happens, and what I think right now is that the backreference variables ($1, $2, $3, etc..) are some sort of special reference variables that automatically dereference themselves when you use them. I'm not even sure if that makes sense, so I was wondering why the above situation occurs and if there is anyway to bypass that problem (without rewriting the regular expression, which I'm sure would be much easier

 

[PaulTEG]

Scoping might be an issue here
nowadays, context variables are cheap, and it makes your code easier to read
HTH
--Paul

 

[MikeLacey]

try

my ($foo, $bar);

at the start of your script

Mike

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It's like this; even samurai have teddy bears, and even teddy bears get drunk.

 

[zyphon08]

I already have the variables defined like that. Also, if it is a scoping issue, wouldn't the output more likely be..

hello and hello

?

 

[icrf]

I can't reproduce the behavior. Putting this alone into a file works as expected:

$_ = 'this is me saying hello, which is really just blah blah blah';
my($foo, $bar);
if(/(hello)/)
{
  $foo = $1;
  if(/(blah)/)
  {
     $bar = $1;
  }
}
print "$foo and $bar";

And if it were a scoping issue, they'd likely take the value of the last assignment. Unless somewhere above you defined both variables to be the same, I don't see how it happened.

Even without strict and my it works. Are $foo and $bar junk variables you use often in the script? Declare once at the beginning and use over and over again? That's a very dangerous practice.

________________________________________
Andrew - Perl Monkey

 

[zyphon08]

Well, $foor and $bar have specific purposes, but I just tried your snippet of code, and you're right... it works as expected. So I fiddled around with the code I was having problems with, and I got it so $foo and $bar aren't equal at the end anymore (my initial prob). There is still one problem, but I'm pretty sure it has to do with my regular expressions and I think I can figure it out from here. Anyways, thanks for you help!