Re^2: Efficient method to replace middle lines only when no match

Thanks for using \K in your post, it made me think a bit more and I came up with a solution that doesn't have a penalty when there's a negative match:

# slow no longer
my $has_field2 = "field1: valueA\nfield2: valueB\nfield3: valueC\n";
$has_field2 .= "........................................\n" x 1000;

$has_field2 =~ s/field1:[\n]*\n\K(?!field2:).*(?=\nfield3:)
                /field2: valueB
                /msx;
[download]

Also, I didn't edit my original post.

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Re^3: Efficient method to replace middle lines only when no match by AnomalousMonk (Archbishop) on Mar 20, 2014 at 15:49 UTC
`$has_field2 =~ s/field1:[\n]\n\K(?!field2:).(?=\nfield3:) /field2: valueB /msx;` [download] Shouldn't the `[\n]\n` after `field1:` in the search pattern be `[^\n]\n` (negated class) instead? The `.` in the search pattern is greedy. Your test string has only one occurrence of the `"field1: valueA\nfield2: valueB\nfield3: valueC\n"` substring. What happens if you test against many occurrences (see below — BTW, I have an updated version of this script that, among other things, uses hi-res timing if you're interested)? Won't the greedy `.` just gobble all intervening occurrences? You have a newline and a lot of blank space in your replacement string; is this what you want? `c:\@Work\Perl\monks\Zu>perl -wMstrict -le "my $s = 'xxxyxxx'; $s =~ s/y /FOO /xms; print qq{'$s'}; " 'xxxFOO xxx'` [download]	[reply] [d/l] [select]

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Re^3: Efficient method to replace middle lines only when no match
by AnomalousMonk (Archbishop) on Mar 20, 2014 at 15:49 UTC

$has_field2 =~ s/field1:[\n]*\n\K(?!field2:).*(?=\nfield3:) /field2: valueB /msx;
[download]

Shouldn't the [\n]*\n after field1: in the search pattern be [^\n]*\n (negated class) instead?
The .* in the search pattern is greedy. Your test string has only one occurrence of the "field1: valueA\nfield2: valueB\nfield3: valueC\n" substring. What happens if you test against many occurrences (see below — BTW, I have an updated version of this script that, among other things, uses hi-res timing if you're interested)? Won't the greedy .* just gobble all intervening occurrences?

You have a newline and a lot of blank space in your replacement string; is this what you want?

c:\@Work\Perl\monks\Zu>perl -wMstrict -le
"my $s = 'xxxyxxx';
 $s =~ s/y
        /FOO
        /xms;
 print qq{'$s'};
"
'xxxFOO
   xxx'
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