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sub 

        # String.sub

(from ruby core)
---
    sub(pattern, replacement)   -> new_string
    sub(pattern) {|match| ... } -> new_string

---

Returns a copy of `self` with only the first occurrence (not all
occurrences) of the given `pattern` replaced.

See [Substitution Methods](#class-String-label-Substitution+Methods).

Related: String#sub!, String#gsub, String#gsub!.

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