Re: position of first matching regex

The special variable @- is an array that contains the offsets from the start of the string to each match. Consider:

use strict;
use warnings;

for my $str ('1 2 3', 'a b c', ' a3 b2 c1') {
    next if $str !~ /\w?([0-9])/;
    my $mpos = $-[0];
    my $cpos = $-[1];
    
    print "Found $1 in '$str' at index $cpos. Overall match started at
+ $mpos\n";
}
[download]

$-[0] accesses the first element of the array - the start of the entire match. $-[1] gives the index of the start of the first capture. The script prints:

Found 1 in '1 2 3' at index 0. Overall match started at 0
Found 3 in ' a3 b2 c1' at index 2. Overall match started at 1
[download]

See the perlvar regular expression variables section. You should take a look at perlretut and perlre too.

Perl is the programming world's equivalent of English

Comment on Re: position of first matching regex Select or Download Code

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Re^2: position of first matching regex by techtaskers.com (Novice) on May 17, 2014 at 14:48 UTC
Yup! There's one of those obvious things I feared: Duh??? ``@'' is an "array" sigil. Wow. I love learning, and it is usually quit a laugh too. Like this time. Nice code! I'm still used to c, just learning perl, and spontaneous variable declarations seem soooo immoral! Just habit. Also, the `next if $str !~ /\w?([0-9])/;` type of code is still new to me. I am assuming that the $- values are keying on the positional declaration within the re. And unlike pos, it does not require m/.../g ? Changed this to: `if ( $filename =~ /([0-9])/ ) { ($startloc = $-[0]); ($alphaloc = $startloc + 4); } print "$startloc$alphaloc ";` [download] The &&'d failed to set $alphaloc if $startloc was zero. (More hilarity!) A case of trying to be clever, instead of being clever. Which now works. Perhaps before I die, I'll remember that perl's arrays are scalar references. Perhaps not. Thank you for your help. This now works, and I can get this done. David	[reply] [d/l] [select]
Re^3: position of first matching regex by GrandFather (Saint) on May 18, 2014 at 10:34 UTC
Why print if the match fails? Note that my code includes strictures (use strict; use warnings;). That will warn you of such unhealthy coding practises. I strongly recommend you use strictures, especially if you are just starting out with Perl. The () around your two assignment statements don't add any value and make understanding the intent of your code harder. `@array` is not a scalar reference. It is the array. Perl is the programming world's equivalent of English	[reply] [d/l]