in reply to Precise backreference semantics in Perl regular expressions

My perl disagrees. 

#!/usr/bin/perl

use strict;
#use warnings;

for my $regexp (
  qr/^((a*)b|a*b?d)*c\2$/,
  qr/^(a*b?d|(a*)b)*c\2$/,
  )
  {
  for my $string (qw( aabadcaa aababdcaa ))
    {
    print "\n$string\n$regexp\n";
    print $string =~ /$regexp/ ? 'Yes' : 'No', "\n";
    }
  }

print <<END;

This is perl 5, version 38, subversion 0 (v5.38.0) built for x86_64-li
+nux-thread-multi

END

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Outputs: 

aabadcaa
(?^:^((a*)b|a*b?d)*c\2$)
No

aababdcaa
(?^:^((a*)b|a*b?d)*c\2$)
No

aabadcaa
(?^:^(a*b?d|(a*)b)*c\2$)
Yes

aababdcaa
(?^:^(a*b?d|(a*)b)*c\2$)
Yes

This is perl 5, version 38, subversion 0 (v5.38.0) built for x86_64-li
+nux-thread-multi

[download]

Replies are listed 'Best First'.
Re^2: Precise backreference semantics in Perl regular expressions
by kikuchiyo (Hermit) on Nov 09, 2023 at 17:26 UTC
[reply]
Re^2: Precise backreference semantics in Perl regular expressions
by tybalt89 (Monsignor) on Nov 10, 2023 at 04:13 UTC

    Opinion... 

    #!/usr/bin/perl

use strict;
#use warnings;

for my $regexp (
  qr/^((a*)b|a*b?d)*c\2$/,
  qr/^(a*b?d|(a*)b)*c\2$/,

  qr/^((a*)b|a*b?d())*c\2$/, # NOTE these two fixed to work the way
  qr/^(?|a*b?d()|(a*)b)*c\1$/, # I think they should work
  )
  {
  for my $string (qw( aabadcaa aababdcaa ))
    {
    print "\n$string\n$regexp\n";
    print $string =~ /$regexp/ ? 'Yes' : 'No', "\n";
    }
  }

print <<END;

This is perl 5, version 38, subversion 0 (v5.38.0) built for x86_64-li
+nux-thread-multi

END

    [download]

    Outputs: 

    aabadcaa
(?^:^((a*)b|a*b?d)*c\2$)
No

aababdcaa
(?^:^((a*)b|a*b?d)*c\2$)
No

aabadcaa
(?^:^(a*b?d|(a*)b)*c\2$)
Yes

aababdcaa
(?^:^(a*b?d|(a*)b)*c\2$)
Yes

aabadcaa
(?^:^((a*)b|a*b?d())*c\2$)
No

aababdcaa
(?^:^((a*)b|a*b?d())*c\2$)
No

aabadcaa
(?^:^(?|a*b?d()|(a*)b)*c\1$)
No

aababdcaa
(?^:^(?|a*b?d()|(a*)b)*c\1$)
No

This is perl 5, version 38, subversion 0 (v5.38.0) built for x86_64-li
+nux-thread-multi

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