Re: Bizarreness in ?PATTERN? and g

Buu's code doesn't seem so bizarre - as many people have commented, it kinda makes sense.

But compare this:


$s="a1 a2 a3";

for (1..2) { 
    print $1 if $s =~ ?a(\d+)?g;
}
[download]

with this:

$s="a1 a2 a3";

print $1 if $s =~ ?a(\d+)?g;
print $1 if $s =~ ?a(\d+)?g;
[download]

I would expect these to be equivalent ... but no, the first example prints "1" and the second prints "1 2".

The plot thickens!

update 2004-06-04 01:41 - added conditionals so the first snippet prints "1" rather than "1 1".

--
eval pack("H*", "7072696e74207061636b2822482a222c202236613631373036382229");
# japh or forkbomb? You decide!

Comment on Re: Bizarreness in ?PATTERN? and g Select or Download Code

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Re^2: Bizarreness in ?PATTERN? and g by CountZero (Bishop) on Jun 04, 2004 at 05:50 UTC
Try printing the value of `$_` before each regex and you will see that you try to match 1 and 2 in your first example as the `for`-loop automagically loads `$_` with the "loop index". As an aside, your first example prints nothing as the regex never matches! CountZero "If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law	[reply] [d/l] [select]
Re^2: Bizarreness in ?PATTERN? and g by revdiablo (Prior) on Jun 04, 2004 at 05:45 UTC
So, hmm. It seems `??` only acts differently if it's inside a loop. The perlop docs mention reset, and `reset` is only really useful for loops, so perhaps `??` is too? Hopefully someone who knows will come clear this up.	[reply] [d/l] [select]
Re^3: Bizarreness in ?PATTERN? and g by ysth (Canon) on Jun 04, 2004 at 07:15 UTC
Each occurence of ?? in code will match only once beteen resets. If you have more than one ??, each one can match once.	[reply]
Re^3: Bizarreness in ?PATTERN? and g by beth (Scribe) on Jun 04, 2004 at 18:20 UTC
japhy took a look at this but I guess he didn't post about it yet. Basically, loops and repeated statements are not interchangeable - they're compiled differently. He suggested running the following two tests, which are quite enlightening: `perl -MO=Terse -e '/x/; /x/;' perl -MO=Terse -e '/x/ for 1, 2'` [download] -- eval pack("H*", "7072696e74207061636b2822482a222c202236613631373036382229"); # japh or forkbomb? You decide!	[reply] [d/l]