Here's what I came up with. This shouldn't fail even if the asdf lines contain colons.

oops, noticed i'd miss abc: lines if there were no asdf lines.

^((\w+):\n((?:[^\n]+\n)+)) -> ^((\w+):\n((?:[^\n]+\n)+)*)
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while ( $data =~ /^((\w+):\n((?:[^\n]+\n)+)*)/gm ) {
    my ( $key, $val ) = ( $2, $3 );
    chomp $val;            ## remove pesky \n\n
    doSomething( $key, $val );    ## store it, print it, ignore it..
}
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