Re: What's happening to my $1?

You are trying to use $1 after a failing match, so basically you deserve whatever's coming to you ;) The contents of the ${\d+} variables are only well-defined if the last (capturing) match was successful. The fact that you were getting the old value was lucky. You should just save $1 after a successful match if you will need it later:

my $last_match;

while ( <DATA> ) {
   if ( /^([A-Z]+)$/ ) { print "In if:   $1\n"; $last_match = $1; }
   else { print "In else: $last_match\n"; }
}
__DATA__
FOO
1234
Xyz
BAR
DFgdfg
[download]

This produces the output you want.

Speculation: As for why it's doing this, I have a guess that as the regex engine goes left to right across the string, it starts matching and filling up the buffer for $1 with uppercase characters, clobbering what was in it before. It doesn't fail until it gets to a lowercase character (when the regex is expecting the end of string), but $1 is already trashed. When the non-matching strings in your __DATA__ started with lowercase letters, the regex could fail before even trying to fill the buffer for $1, so it was not clobbered and the old value remained.

Why you still ended up getting exactly the old first character though is a mystery to me.

blokhead

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Re: Re: What's happening to my $1? by Not_a_Number (Prior) on Jan 20, 2004 at 22:23 UTC
You are trying to use $1 after a failing match, so basically you deserve whatever's coming to you ;) Thanks, blokhead. That's more or less what I'd intuited. But, in that case: 1) Why doesn't the 'failing match' clobber `$1` in my first two snippets? 2) With respect to the docs: The numbered variables ($1, $2, $3, etc.) ... are all dynamically scoped until the end of the enclosing block or until the next successful match, whichever comes first. This seems to suggest that `$1` (provided that it stays in scope) should not change until a match succeeds, rather than being clobbered if a match fails (which, I'm sure you'll agree, is not the same thing...). Why you still ended up getting exactly the old first character though is a mystery to me. To me too... Still Confused, dave	[reply] [d/l] [select]

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Re: Re: What's happening to my $1?
by Not_a_Number (Prior) on Jan 20, 2004 at 22:23 UTC

You are trying to use $1 after a failing match, so basically you deserve whatever's coming to you ;)

Thanks, blokhead. That's more or less what I'd intuited. But, in that case:

1) Why doesn't the 'failing match' clobber $1 in my first two snippets?

2) With respect to the docs:

The numbered variables ($1, $2, $3, etc.) ... are all dynamically scoped until the end of the enclosing block or until the next successful match, whichever comes first.

This seems to suggest that $1 (provided that it stays in scope) should not change until a match succeeds, rather than being clobbered if a match fails (which, I'm sure you'll agree, is not the same thing...).

Why you still ended up getting exactly the old first character though is a mystery to me.

To me too...

Still Confused,

dave

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