You can find bits and not replace them using lookahead and lookbehind assertions:

$bleh =~ s/(?<=-)(?=b|c)/:/g;
[download]

For more details see perlman:perlre or Super Search for "lookahead assertions" in the text +/- "tachyon" as author as I know I have written a summary on this a while back.

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print