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Re: Debugging Regexes

by fletcher_the_dog (Friar)
on Jun 28, 2004 at 17:49 UTC ( #370270=note: print w/replies, xml ) Need Help??


in reply to Debugging Regexes

Why your regex matches the string can be explained like this:
"(?=hello)" matches "hello" ".*" matches "hello Ga" "[^G]" matches "g" "[^a]" matches "s" ".*" matches nothing
Your regex properly skips matching [^G][^a] with "Ga" but will happily match stuff after that. You probably want to do something like this with a negative look ahead:
( "hello Gags" =~ /^(?=hello)(?!.*Ga/ )&& print ("Matched") || print ( +"Unmatched")
Update
To answer your question about how debugging, I find that throwing in a few capturing parens, can often help you to see what is being matched. Here is is a simple example:
use strict; ( "hello Gags" =~ /^(?=hello)(.*)([^G][^a])(.*)$/ ) ? matches() : pri +nt ("Unmatched"); sub matches { no strict 'refs'; for (1..10) { my $tmp = ${$_} or next; print "\$$_ = '$tmp'\n"; } return 1; } __OUTPUT__ $1 = 'hello Ga' $2 = 'gs'

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