cat << EOF | sed -r '1,/<c>.*<\/c>/s#<c>(.*)</c>#<e>\1</e>#'<a><b>...</b><c>...</c><c>...</c><d>..</d></a>EOF
Standard input is empty
<a> <b>...</b> <e>...</e> <c>...</c> <d>..</d> </a>
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