What does perl special variable $-[0] and $+[0] means

Question

I want to know the meaning of perl special variables $-[0] and $+[0]

I have googled and found that $- represent number of lines left on the page and $+ represent the last bracket matched by the last search pattern.

But my question is what $-[0] and $+[0] means in context of regular expressions.

Let me know if code sample is required.

Answer 1

See perldoc perlvar about @+ and @-.

$+[0] is the offset into the string of the end of the entire match.

$-[0] is the offset of the start of the last successful match.

Answer 2

These are both elements from an array (indicated by the square brackets and number), so you want to search for @- (the array) and not $- (an unrelated scalar variable).

The commend

perldoc perlvar 

explains Perl's special variables. If you search in there for @- you will find.

$-[0] is the offset of the start of the last successful match. $-[n] is the offset of the start of the substring matched by n-th subpattern, or undef if the subpattern did not match.

Answer 3

Adding example for better understanding of $-[0],$+[0]

Also adding info on variable $+

use strict;
use warnings;

my $str="This is a Hello World program";
$str=~/Hello/;

local $\="\n"; # Used to separate output 

print $-[0]; # $-[0] is the offset of the start of the last successful match. 

print $+[0]; # $+[0] is the offset into the string of the end of the entire match. 

$str=~/(This)(.*?)Hello(.*?)program/;

print $str;

print $+;                    # This returns the last bracket result match 

Output:

D:\perlex>perl perlvar.pl
10                           # position of 'H' in str
15                           # position where match ends in str
This is a Hello World program
 World