position of the last match in RE

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I want to know the position of a character the regular expression matches last time. For ex:

$_ = "abcdmefg";
$_ = /m/;
print "$&\t$`\t$'\n";
[download]

It prints:     m   abcd   efg
[download]

The above printed matched, prematch and after match. But I like to know the position of the charactr 'm' in the string. Then I used while loop like this:

$_ = "abcdmefg";
while(m/m/g)
{
   print "matched 'm' at ",pos,"\n";
}
[download]

Then it prints: matched 'm' at 5. Is there anyway to print the position without while loop? I treid to print using pos in the first example, but does not work. Can you pl. help me? Thanks Ashok

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Re: position of the last match in RE by chipmunk (Parson) on Mar 01, 2001 at 08:30 UTC
In order for pos to remain set, you need to use the /g modifier on the regex. This is why the snippet with the while loop works. So, just use /g without the while loop: `$_ = "abcdmefg"; if ($_ =~ /m/g) { print "matched 'm' at ",pos,"\n"; }` [download] However, if you're just looking for fixed substrings, you may prefer to use index instead: `$_ = "abcdmefg"; if (($pos = index($_, 'm')) >= 0) { print "found 'm' at ", $pos, "\n"; }` [download] Keep in mind that pos returns the location where the previous match ended, while index returns the location where the substring begins. Thus, these two snippets give 5 and 4 respectively.	[reply] [d/l] [select]
Re: position of the last match in RE by chromatic (Archbishop) on Mar 01, 2001 at 08:30 UTC
The while part isn't what sets pos, it's the /g modifier on a match. Simply say: `$_ = "abcdmefg"; m/m/g; print "Matched 'm' at ", pos, "\n";` [download] If you don't need to match a full regex, you can use the index or rindex functions.	[reply] [d/l]