string.gsub(s, pattern, replace [, n])
This is a very powerful function and can be used in multiple ways. Used simply it can replace all instances of the pattern provided with the replacement. A pair of values is returned, the modified string and the number of substitutions made. The optional fourth argument n can be used to limit the number of substitutions made:
> = string.gsub("Hello banana", "banana", "Lua user")
Hello Lua user 1
> = string.gsub("banana", "a", "A", 2) -- limit substitutions made to 2
bAnAna 2
If a capture is used this can be referenced in the replacement string using the notation %capture_index, e.g.,
> = string.gsub("banana", "(an)", "%1-") -- capture any occurances of "an" and replace
ban-an-a 2
> = string.gsub("banana", "a(n)", "a(%1)") -- brackets around n's which follow a's
ba(n)a(n)a 2
> = string.gsub("banana", "(a)(n)", "%2%1") -- reverse any "an"s
bnanaa 2
If the replacement is a function, not a string, the arguments passed to the function are any captures that are made. If the function returns a string, the value returned is substituted back into the string. Just like string.find() we can use regular expressions to search in strings. Patterns are covered in the PatternsTutorial.
> = string.gsub("Hello Lua user", "(%w+)", print) -- print any words found
Hello
Lua
user
3
> = string.gsub("Hello Lua user", "(%w+)", function(w) return string.len(w) end) -- replace with lengths
5 3 4 3
> = string.gsub("banana", "(a)", string.upper) -- make all "a"s found uppercase
bAnAnA 3
> = string.gsub("banana", "(a)(n)", function(a,b) return b..a end) -- reverse any "an"s
bnanaa 2