Source code in the brat programming language

str = "I am a string"

true? str.match(/string$/)
 { p "Ends with 'string'" }

false? str.match(/^You/)
 { p "Does not start with 'You'" }

# Substitute in copy

str2 = str.sub(/ a /, " another ")

p str    # original unchanged
p str2   # prints "I am another string"

# Substitute in place

str.sub!(/ a /, " another ")

p str    # prints "I am another string"

# Substitute with a block

str.sub! /a/
 { match | match.upcase }

p str    # prints "I Am Another string"