For a couple additions to chrestomanci's advice:

1. 1) I'd recommend that you use values instead of keys since you're ignoring the key data.
2. 2) Also, be sure to use the $ anchor instead of ^ for the end of string boundary

foreach my $plf_vals (values %Hash_plfdata) {
    my ($base_p4path) = grep {m{/\Q$file_name\E}i && !m{\.plf$}} @$plf
+_vals;
    print "BASE p4 path:$base_p4path\n";
}
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