Re: I need a better regex with a literal in it

[ToddAndMargo via perl6-users]

On 10/23/21 17:37, Bruce Gray wrote:

On Oct 23, 2021, at 6:43 PM, ToddAndMargo via perl6-users 
<perl6-us...@perl.org> wrote:

Hi All,

Wish I had a Q[;;;] expression inside a regex, but I don't

This is my notes on how to do a regex with a special
characters in it:

     Regex with literals in it:
        $JsonAddr ~~ s| (';') .* ||;

It "usually" works.


Unfortunately this one hangs my program (I am slicing
up a web page):

$NewRev ~~ s/ .*? ('Release Notes <strong>V') //;

I need a better way of doing the above.

Many thanks,
-T

Just anchor the start of the pattern, using `^` :
        $NewRev ~~ s/ ^ .*? ('Release Notes <strong>V') //;


In the code below:
     * Target_V is matched by the original pattern, at high speed.
     * Target_V is matched by the anchored pattern, at high speed.
     * Target_Z hangs the original pattern.
     * Target_Z is correctly fails at match the anchored pattern, at high speed.

my $target_V = 'Release Notes <strong>V';       # Will     match pattern(s) 
below
my $target_Z = 'Release Notes <strong>Z';       # Will not match pattern(s) 
below

# Uncomment one of these two lines:
my $target = $target_V;
# my $target = $target_Z;

# Simulate a big HTML page:
my $NewRev = ('abcdefghijklmnopqrstuvwxyz' x 100) ~ $target
            ~ ('ABCDEFGHIJKLMNOPQRSTUVWXYZ' x 100) ~ $target
            ~ ('12345678901234567890123456' x 100);


# Uncomment one of these two lines:
$NewRev ~~ s/   .*? ('Release Notes <strong>V') //; # Original
# $NewRev ~~ s/ ^ .*? ('Release Notes <strong>V') //; # Anchored

Hi Bruce,

I did fix the hang.  I was accidentally feeding the
regex a nul string.

I am not understanding what you mean by "anchor"

-T