Perl模式匹配无法按预期工作

Question

I'm trying to match values, which may be comma separated, using a regex. Basically, I want to return true if any value in the string does NOT have 3g or 3k starting in the 3rd position.

My test code is as follows:

my @a = ('in3g123456,dh3k123456,dhec110101','dhec110101,dhec123456','in3g123456,dh3k123456', 'c3kasdf', 'usdfusdufs3gsdf' );

foreach (@a) {
  print $_;
  say $_ =~ /(?:^|,)\w{2}[^(?:3G|3K)]/i ? " true" : " false";
}

This returns

in3g123456,dh3k123456,dhec110101 true
dhec110101,dhec123456 true
in3g123456,dh3k123456 false
c3kasdf false   <- whaaaaaaaat?
usdfusdufs3gsdf true

I don't understand why the 4th one is not true. Any help would be appreciated.

Answer 1

[^(?:3G|3K)] reads as "any character but ( , ? , etc."

                      failed
                      v
        c3            kasdf
/(?:^|,)\w{2}[^(?:3G|3K)]/i

Use this:

/(?:^|,)\w{2}(?!3G|3K)/i

Demo: https://regex101.com/r/P2XsgN/1 .

Answer 2

How about /\\b\\w{2}(?!3g|3k)/i .

\\b matches the empty string at the beginning or end of a word. Slightly simpler equivalent to (^|,) in this situation.

(?!foo) is a zero-width negative lookahead assertion. So, matches the empty string as long as it's not followed by a substring that matches foo .

Answer 3

You can also split the string first, instead of parsing everything with a regex. That is far more flexible and maintainable, and easier.

When processing the list of the extracted "values" you can match any character twice then your pattern, /^..$patt/ . The module List::MoreUtils is useful (and fast) for list manipulations, and its notall function is tailor-made for your condition.

use warnings 'all';
use strict;
use List::MoreUtils qw(notall);

my $file = '...';
open my $fh, '<', $file or die "Can't open $file: $!";

while (<$fh>)
{
    my $res = notall { /^..(?:3k|3g)/ } split /,/;

    print "$_: " . ($res ? 'true' : 'false'), "\n";
}

I presume that you read from a file. If not, replace while (<$fn>) with for (@strings) .

The notall function returns true if any element of the list fails the condition.

The split by default uses $_ so we only need the pattern. Here it is simply , but the pattern takes a regex so one can match separators flexibly. For example, this /[,\\s]+/ splits on any amount of , and/or whitespace. So ,, , in a string is matched as a separator, as well as , or space(s).

When applied to the array with your strings the above prints

in3g123456,dh3k123456,dhec110101: true
dhec110101,dhec123456: true
in3g123456,dh3k123456: false
c3kasdf: true
usdfusdufs3gsdf: true

Answer 4

You could use substr to get data at 3rd and 4th position and then compare it with (3g|3k) .

substr $_,2,2

---

#!/usr/bin/perl
use strict;
use warnings;

my @a = ('in3g123456,dh3k123456,dhec110101','dhec110101,dhec123456','in3g123456,dh3k123456', 'c3kasdf', 'usdfusdufs3gsdf' );

foreach (@a) {
  my @inputs = split /,/,$_;
  my $flag = 0;
  foreach (@inputs){
    $flag = 1 unless ((substr $_,2,2) =~ /(3g|3k)/);
  }
  $flag ? print "$_: True\n" : print "$_: False\n";
}

Output:

in3g123456,dh3k123456,dhec110101: True
dhec110101,dhec123456: True
in3g123456,dh3k123456: False
c3kasdf: True
usdfusdufs3gsdf: True

Demo