Regex AND NOT with zero-width negative lookahead assertion

mldvx4 has asked for the wisdom of the Perl Monks concerning the following question:

I am trying to use zero-width negative lookahead assertions to add an AND NOT logical clause to my pattern. I wish to match /aaa/ and /aaa\/aaa/ but not /aaa/aaa/ which is to say a span delimited by unescaped slashes. What I have so far matches too much:

#!/usr/bin/perl

use strict;
use warnings;

while (<DATA>) {

    # print $+{pattern},qq(\n) if (

    # for now, show the whole line
    print if (
        m,
        ^
        (?!\x23)
        (?:.*?)
        (?<pattern>
        m?
        (?<delimiter>[/])
        (?:(?:\\?+.)*?)*?
        \g{delimiter}
        )
        ,x
        );
}


__DATA__

#!/usr/bin/perl
foo
bar
foo/bar
/src/bin/oops/otehnoes
if(/ok .*$/) {
    print "not OK\n";
}
# skip a comment
if(m/a good match/( {
    print "not ok\n";
}

# do not /print/ this line either
$string =~ s/[a-f]//g; # but print this line
( $string ) = ( $string =~ /(show this)/));
/but show\/this, too/
my $butdontprintthis = "/var/cache/dictionaries-common";
[download]

However, I have not found a successful way to match /aaa/ while at the same time rejecting /aaa/aaa/

What should I append towards the end of the pattern to ensure that /aaa/aaa/aaa/ and other similar strings are not accepted by the pattern yet /aaa/ alone would be? I have tried many scores of permutations of what to tack on, but no sucess yet. The script above produces the following result:

/src/bin/oops/otehnoes
if(/ok .*$/) {
if(m/a good match/( {
$string =~ s/[a-f]//g; # but print this line
( $string ) = ( $string =~ /(show this)/));
/but show\/this, too/
my $dontprint this = "/var/cache/dictionaries-common";
[download]

But it should produce the following instead:

if(/ok .*$/) {
if(m/a good match/( {
$string =~ s/[a-f]//g; # but print this line
( $string ) = ( $string =~ /(show this)/));
/but show\/this, too/
[download]

Comment on Regex AND NOT with zero-width negative lookahead assertion Select or Download Code

Replies are listed 'Best First'.
Re: Regex AND NOT with zero-width negative lookahead assertion by hippo (Archbishop) on Mar 25, 2020 at 12:13 UTC
I think this might do what you want. use strict; use warnings; use Test::More tests => 1; my $want = <<'EOT'; if(/ok .$/) { if(m/a good match/( { $string =~ s/[a-f]//g; # but print this line ( $string ) = ( $string =~ /(show this)/)); /but show\/this, too/ EOT my $have = ''; while (<DATA>) { $have .= $_ if m~^(?!#)[^/]/[^/]+(\\/\|/(?!\w+/?))~; } is $have, $want; __DATA__ #!/usr/bin/perl foo bar foo/bar /src/bin/oops/otehnoes if(/ok .*$/) { print "not OK\n"; } # skip a comment if(m/a good match/( { print "not ok\n"; } # do not /print/ this line either $string =~ s/[a-f]//g; # but print this line ( $string ) = ( $string =~ /(show this)/)); /but show\/this, too/ my $butdontprintthis = "/var/cache/dictionaries-common"; [download]	[reply] [d/l]
Re^2: Regex AND NOT with zero-width negative lookahead assertion by mldvx4 (Hermit) on Mar 25, 2020 at 13:34 UTC
Thanks. (And thanks to those below, too.) That seems to achieve the desired results, if I escape the pound sign (#) there. Otherwise that gets interpreted as a comment.	[reply]
Re^3: Regex AND NOT with zero-width negative lookahead assertion by hippo (Archbishop) on Mar 25, 2020 at 13:43 UTC
How odd. It works fine exactly as posted for me in Perl 5.20.3. Which Perl version are you using which requires the escape? Update: also tested successfully on v5.10.1, v5.16.3, v5.26.1 and v5.30.0.	[reply]
Re^4: Regex AND NOT with zero-width negative lookahead assertion by Your Mother (Archbishop) on Mar 25, 2020 at 14:04 UTC
Re^4: Regex AND NOT with zero-width negative lookahead assertion by AnomalousMonk (Archbishop) on Mar 26, 2020 at 03:41 UTC
Re: Regex AND NOT with zero-width negative lookahead assertion by Veltro (Hermit) on Mar 25, 2020 at 13:07 UTC
Haven't looked at hippo's answer yet but in the mean while I tried: `#!/usr/bin/perl use strict; use warnings; while( <DATA> ) { chomp ; print "$_ -> " ; if ( m/^\/(?:[^\/]\|(?<=\\)\/)+\/$/ ) { print " matched\n" ; } else { print " not matched\n" ; } } __DATA__ /aaa/ /\a\a\a\/\b\b\b/ /aaa\/bbb/ /aaa/bbb/` [download] Output `/aaa/ -> matched /\a\a\a\/\b\b\b/ -> matched /aaa\/bbb/ -> matched /aaa/bbb/ -> not matched` [download]	[reply] [d/l] [select]
Re: Regex AND NOT with zero-width negative lookahead assertion by Anonymous Monk on Mar 25, 2020 at 12:41 UTC
You might want to take a look at Regexp::Common.	[reply]
Re^2: Regex AND NOT with zero-width negative lookahead assertion by cxw (Scribe) on Mar 28, 2020 at 00:24 UTC
Specifically, this might serve - `use Regexp::Common qw /delimited/; $str =~ /^$RE{delimited}{-delim=>'/'}$/;` [download] The `$RE{delimited}` regex accepts backslash escapes by default.	[reply] [d/l] [select]