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End of Life Ruby 3.1 has reached end of life and gets no more fixes. Switch to Ruby 4.0 →

instance method

String#ascii_only?

str.ascii_only? → true or false

Returns true for a string which has only ASCII characters.

Example
"abc".force_encoding("UTF-8").ascii_only?          #=> true
"abc\u{6666}".force_encoding("UTF-8").ascii_only?  #=> false
See also #[]= #b #[] #bytes also in 4.1 · 4.0 · 3.4 · 3.3 · 3.2 · 3.0