Consider the following code.

print chg("word", qr/(\d)/);   # print "nope"
"2" =~ /(2)/;
print chg("word", qr/(\d)/);   # print "yes"

sub chg {
    $_[0] =~ $_[1];
    return $1 ? "yes\n" : "nope\n";
}

[download]

"2" =~ /(2)/ sets $1 to 2, which inadvertently affects chg() since chg() checks $1 for valid condition but $1 was set from outside.

If I'm using someone else's code where it might be using $1 for various things that I might not be aware of, is there anything I can do to avoid such a trap? It's kind of hard to track down such things in a large script. Thanks.

In reply to $1 trap by chunlou

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