The leading $and the middle \w are common between patterns. In fact, all that's required is to require a closing ) only when there was an opening (.

Using a less well known feature

\$ # Our '$' prefix
(?:
    # Optionally *don't* find the opening paren.
  |
    (\() # Optionally find the opening paren
)
(\w+) # The middle part is captured in $2
(?(1)\)) # Require a closing paren only if $1 matched.

[download]

Merely removing the prefix

\$ # Our '$' prefix
( # Capture into $1
    (?:
        \w+ # Plain word.
      |
        \( \w+ \) # A word with parentheses around it.
    )
)

[download]

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In reply to Re^2: How do I avoid double substitution when replacing many patterns? by diotalevi
in thread How do I avoid double substitution when replacing many patterns? by kyle

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