This code is neither robust nor efficient nor general. But it's short and fun. Making it any of those things is not difficult, but it won't be do-able in 56 chars.

It doesn't deal with escaped or quoted parens -- i.e. they are treated like any other. It doesn't deal with nulls in the input very well, to make it do that would cost 3 extra chars. It doesn't let you know where you're unbalanced, but simply prints `1' if the input is balanced and prints nothing if it's not. Oh, and it requires 5.6.0 or better.

Give it a filename to check for balancing on the command line, or run it as shown below exactly and give it text to check on standard input.

-dlc

perl -n0e'$r=qr/(?>[^()]*)|\((??{$r})+\)/;print/^$r*$/'
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