***This is not an RE***. You need m"this" syntax to make it an RE. The only time you can not use m is if you have syntax $foo =~ /this/ Using the / char as the RE delimiter makes the m implicit. Your 'RE' uses " as the delimiter so needs the m. It does not do what I expect the original programmer thought it would. Here is what it does: 

use warnings;
my %flows = ( '0' => 1, '00' => 2, '0$' => 3, '0$more' => 4, 'foo0$' =
+> 5 );

foreach (keys %flows) {
    # loop through keys of %flows setting $_ to each key in turn
    if (!($_ =~ "^0\$")) {
        print "Orig $_ not matched\n";
    } else {
        print "Orig $_ matched\n";
    }

    if (!($_ =~ m"^0\$")) {
        print "RE   $_ not matched\n";
    } else {
        print "RE   $_ matched\n";
    }
    print $/;
}


__DATA__
Orig 0 matched
RE   0 not matched

Orig 00 not matched
RE   00 not matched

Orig 0$more not matched
RE   0$more matched

Orig 0$ not matched
RE   0$ matched

Orig foo0$ not matched
RE   foo0$ not matched

[download]

I am intrigued it is not a syntax error or warning. It appears that the intent is to do something if the hash key does not start with the 2 literal chars '0$'. It does not do that as you can see.

cheers

tachyon

In reply to Re: what function of this Regular Expression? by tachyon
in thread what function of this Regular Expression? by iwanthome

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