If you're brave, you can construct a regex which you can bang your various directories against. This can be done quite simply like so:
my $skip = join ('|', map {quotemeta} keys %$config_dirs);
This will look something like "/usr/bin|/home|/var" or what have you. Now you can just go and check against this, like dragonchild suggested, but with a slight mod: 
foreach (keys %$dirs)
{
    next if /^($skip)/;
    # Do stuff
}

[download]
Presumably if the value of $skip does not change within your program, you can use the /o option to only "compile once" your regular expression.

In reply to Re^3: Efficiency Question by tadman
in thread Efficiency Question by PrimeLord

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