Re: in the elemetns of programming perl , I need help with 2 lines that I don't understand

Rob Dixon wrote:
> It's always confusing when a program written in one language (here, Perl)
> creates a program in another (this script is building regular expressions).
>
> Look at the strings those lines are generating.
>
> use strict;
> use warnings;
>
> local @ARGV = qw/A B C/;
>
> my $or_pattern = '.*(?:' . join('|', @ARGV) . ')';
> my $and_pattern = join('', map{"(?=.*$_)"} @ARGV);
>
> print "Or pattern:  $or_pattern\n";
> print "And pattern: $and_pattern\n";
>
> **OUTPUT**
>
> Or pattern:  .*(?:A|B|C)
> And pattern: (?=.*A)(?=.*B)(?=.*C)
>
> Now can you understand those as regular expressions? The former uses
> non-capturing parentheses (?: ... ) to find any one of the values anywhere in
> the string, while the latter uses a lookahead (?= ... ) to find a point in the
> string after which all three of the values appear anywhere.
>
> HTH,
>
> Rob
>   
This is VERY clear. thank you understand it now!!!