If you know the position of the fields in the line there's no reason you can't use a regex to do the job. Capture the 10th field then use a back-reference to the 10th in the 13th position.

use strict;
use warnings;

my @strings = qw{
   0;1;2;3;4;5;6;7;8;9;10;11;12;13
   0;1;2;3;4;5;6;7;8;9;10;11;9;8
   0;1;2;3;4;5;6;7;8;9;10;11;99
   0;1;2;3;4;5;6;7;8;9;10;11;9
   0;1;2;3;4;5;6;7;8;;10;11;;13
   0;1;2;3;4;5;6;7;8;;10;11;12;13
   };

my $rxByPosn = qr
   {(?x)
       \A            # Start of string
       (?:[^;]*;){9} # Nine fields/delimiters
       ([^;]*)       # Capture 10th field, which
                     #   could be blank
       ;             # Delimiter
       (?:[^;]*;){2} # Two more fields/delimiters
       \1            # 13th field must match 10th
       (?:;|\z)      # Delimiter or end of string
   };

foreach my $string ( @strings )
{
    print
       qq{String - $string\n},
       $string =~ $rxByPosn
       ? qq{     Col. 10 matches col. 13\n} 
       : qq{     Cols 10 and 13 differ\n} ;
}
[download]

The output.

String - 0;1;2;3;4;5;6;7;8;9;10;11;12;13
     Cols 10 and 13 differ
String - 0;1;2;3;4;5;6;7;8;9;10;11;9;8
     Col. 10 matches col. 13
String - 0;1;2;3;4;5;6;7;8;9;10;11;99
     Cols 10 and 13 differ
String - 0;1;2;3;4;5;6;7;8;9;10;11;9
     Col. 10 matches col. 13
String - 0;1;2;3;4;5;6;7;8;;10;11;;13
     Col. 10 matches col. 13
String - 0;1;2;3;4;5;6;7;8;;10;11;12;13
     Cols 10 and 13 differ
[download]

I hope this is of use.

Cheers,

JohnGG

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