Re: Text matching repost

How about a different approach?

#!/usr/bin/perl

use strict;
use warnings;
my ($start, $stop) = (qr '#ifdef|#if defined', qr '#endif');


open INPUT, '<', 'monks23.dat' or die "Error opening input: " . $!;
while (<INPUT>) {
    if (/$start/ .. /$stop/) {
        # Print the lines themselves
        if (/$start/ or /$stop/) { print; }
        # Skip the rest
        next;
    }
    print;
}

close INPUT;
[download]

Glad I've finally found a useful non-numeric-iterating purpose for .. :)
Edit: Added comments, removed unnecessary regex escaping

Comment on Re: Text matching repost Select or Download Code

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Re^2: Text matching repost by Neighbour (Friar) on Jun 18, 2012 at 12:19 UTC
I later realised that instead of using `if (/$start/ or /$stop/) { print; }` [download] I could just as well use (and more efficient too): `if ($&) { print; }` [download] The meaning of `$&` is explained in perlvar as The string matched by the last successful pattern match. You can also use `$MATCH` if you `use English;`	[reply] [d/l] [select]
Re^3: Text matching repost by afoken (Chancellor) on Jun 18, 2012 at 14:24 UTC
I could just as well use (and more efficient too): `if ($&) { print; }` [download] Ummm, no. `$&` is one of the "ugly three" variables (the other two are $` and `$'`) that kill performance. From perlvar: The use of this variable anywhere in a program imposes a considerable performance penalty on all regular expression matches. To avoid this penalty, you can extract the same substring by using `@-`. Starting with Perl 5.10, you can use the `/p` match flag and the `${^MATCH}` variable to do the same thing for particular match operations. Apart from that, it may work for this special problem, but it does not work if `$&` evaluates to false: `perl -E '$x="a0b"; $x=~/0/; say $&; if ($&) { die "not reached!" } if + ($x=~/0/) { say "matched zero" }'` [download] Output: `0 matched zero` [download] Alexander -- Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)	[reply] [d/l] [select]
Re^4: Text matching repost by Neighbour (Friar) on Jun 19, 2012 at 06:39 UTC
Good call, it shall be `if (scalar @-) { print; }` [download] then :)	[reply] [d/l]
Re^2: Text matching repost by prassi (Acolyte) on Jun 18, 2012 at 10:45 UTC
Hi, What kind of regex is this the above you mentioned, can you point me to some document on more understanding on this. Thanks, -Prassi	[reply]
Re^3: Text matching repost by Neighbour (Friar) on Jun 18, 2012 at 11:09 UTC
`qr` is explained in Regexp Quote Like Operators. It's basically an easy way to put regular expressions in variables.	[reply] [d/l]