Here \ is a special character before @ so you have to escape it by \\.

Then do slight change in replacement part.

/"<idl package=\"".lc($1)."\" name=\"$3\" anker=\"$4\"\/>"/esi;

updated

Prasad

In reply to Re^3: Regexp matched part to lower case by prasadbabu
in thread Regexp matched part to lower case by tomson

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