more compact version of your code. And you should use '-e' test instead of '-t'

#!/usr/bin/perl
sub FileFinder {
   my ($target, @dir) = @_;
   return (grep {-e $_} map {"$_/$target"} @dir)[0];
}
 
open(F, FileFinder('FileFinder.pl', qw(some/ dirs/ ./)) || die "File n
+ot found") or die $!;
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