There should be a "g" at the end of those lines:

my @find = $line[$i] =~ /(?:\A|\t)(abc\d+)(?=\t|\z)/g;
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otherwise the regexp matches only once instead of searching for all abc<some_number>.

And if you happen to need to count each of the abc<some_number> separately you can either process the @find:

my @find = $line[$i] =~ /(?:\A|\t)(abc\d+)(?=\t|\z)/
my %count;
$count{$_}++ for @find;
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or skip building the array

while ($line[i] =~ /(?:\A|\t)(abc\d+)(?=\t|\z)/g) {
    $count{$1}++;
}
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