This will print all files that end in .h* or just .c. It will list .html files .htm files, etc. Surround the \.h|\.c with parens. Change

if ( $entry =~ /\.h|\.c$) {
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to

if ( $entry =~ /(\.h|\.c)$) {
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It also won't catch files that end in .H or .C if for some reason those are in caps. You can adjust accordingly.