When you think of a subset of an array, think grep.
Use map only when you think of transforming one thing into another.
Perl variables can be interpolated into a regex expression.

my $pat = "somepattern";
@simMatches = grep{/$pat$num/} @simMatches; # subset of @simMatches
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Show a couple of lines of actual data and this can all become clear.
$1 or $2 are regex capture variables that don't seem to play a role here.