How to check if matching text is found in a string in Lua?

Question

I need to make a conditional that is true if a particular matching text is found at least once in a string of text, e.g.:

str = "This is some text containing the word tiger."
if string.match(str, "tiger") then
    print ("The word tiger was found.")
else
    print ("The word tiger was not found.")

How can I check if the text is found somewhere in the string?

Answer 1

There are 2 options to find matching text; string.match or string.find.

Both of these perform a Lua patten search on the string to find matches.

---

string.find()

string.find(subject string, pattern string, optional start position, optional plain flag)

Returns the startIndex & endIndex of the substring found.

The plain flag allows for the pattern to be ignored and intead be interpreted as a literal. Rather than (tiger) being interpreted as a pattern capture group matching for tiger, it instead looks for (tiger) within a string.

Going the other way, if you want to pattern match but still want literal special characters (such as .()[]+- etc.), you can escape them with a percentage; %(tiger%).

You will likely use this in combination with string.sub

Example

str = "This is some text containing the word tiger."
if string.find(str, "tiger") then
  print ("The word tiger was found.")
else
  print ("The word tiger was not found.")
end

---

string.match()

string.match(s, pattern, optional index)

Returns the capture groups found.

Example

str = "This is some text containing the word tiger."
if string.match(str, "tiger") then
  print ("The word tiger was found.")
else
  print ("The word tiger was not found.")
end