I think you are trying to do something like show which lines have repeated words in them. The problem description in your original post is a little unclear and seemed to cover several requirements but your code hints at this solution. Given this input file:

this and that
fish and chips and mushy peas
the cat and catkin
boom bang boom
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This code:

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

my $inputFile = q{spw888564.txt};
open my $inputFH, q{<}, $inputFile
   or die qq{open: < $inputFile: $!\n};

while ( <$inputFH> )
{
    next unless m{(\w+).*\b\1\b};
    print qq{Found '$1' repeated in: $_};
}

close $inputFH
   or die qq{close: < $inputFile: $!\n};
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Produces this output:

Found 'and' repeated in: fish and chips and mushy peas
Found 'boom' repeated in: boom bang boom
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I hope I have guessed correctly and this is some help but please ask more questions if things are unclear.

• When you do readline and put it into $line, $_ does not get a value (see perlintro)
• There is no need to write $_ =~ /.../ because by default /.../ matches against $_, but in this case you should be matching against $line
• Use strict warnings and diagnostics or die
• Read this if you want to cut your development time in half!
• For them to be readable, you must enclose code/data in <code></code> (or <c></c> for short) tags