String API


API docs for Space Lua's string module.

Note: since string values set string as their meta table, these APIs can also be called as method calls on strings directly. For instance: someString:startsWith("h") is equivalent to string.startsWith(someString, "h").

Lua Pattern Matching


Lua patterns are not regular expressions. Space Lua makes a good effort at translating Lua patterns to regex to run in a Javascript environment, but there are two main differences:

  1. Magic characters ^$()%.[]*+-? must be escaped to represent their character. Standard Lua patterns do not require escaping magic characters when they are not contextually magic (e.g. %d-- is a valid Lua pattern where the second hyphen is not magic). Space Lua may have unexpected results when expecting an un-escaped magic character to behave like a character.
  2. In Space Lua, the repetition magic characters (?, *, +, and -) will apply to captures in patterns. They do not in standard Lua.


Additionally, the patterns for the nth captured string (%*n*), balanced match (%b*xy*), and frontier pattern (%f[set]) in Lua will likely not be supported.

As noted below, the operations string.matchRegex and string.matchRegexAll
leverage regex in Javascript--not Space Lua patterns.

Here are some valid Lua patterns with different matches (or outright errors) in Space Lua:

print(string.match("1234", "(%d)+"))
-- prints "4" in Space Lua (last match of the captures)
-- prints "nil" in Lua (repetition magic does not work on captures)

print(string.match("*", "*"))
-- invalid regex in Space Lua ("*" is not escaped)
-- prints "*" in Lua

print(string.match("2024-03-14", "%d+-(%d+)-%d+"))
-- invalid regex in Space Lua (the "-"s are not escaped")
-- prints "03" in Lua


String Operations


string.byte(s, i?, j?)

Returns the numeric codes of characters in string s from position i to j. If j is not provided, defaults to i.

Example:
print(string.byte("Hello", 1))  -- prints: 72 (ASCII code for 'H')


string.char(...)

Returns a string from given ASCII codes.

Example:
print(string.char(72))  -- prints: H


string.find(s, pattern, init?, plain?)

Looks for the first match of pattern in string s. Returns start and end indices of match.

Example:
local start, end_ = string.find("Hello", "l")
print(start)  -- prints: 3 (first 'l' position)


string.format(format, ...)

Returns a formatted string using C-style format specifiers.

Example:
print(string.format("Name: %s, Age: %d", "John", 30))  -- prints: Name: John, Age: 30
print(string.format("Pi: %.2f", 3.14159))             -- prints: Pi: 3.14


string.gsub(s, pattern, repl, n?)

Returns a copy of s in which all (or the first n) occurrences of pattern have been replaced by repl.

Example:
-- Simple string replacement
local result, count = string.gsub("hello world", "hello", "hi")
print(result, count)  -- prints: hi world 1

-- Multiple replacements with limit
result = string.gsub("hello hello hello", "hello", "hi", 2)
print(result)  -- prints: hi hi hello

-- Function replacement
result = string.gsub("hello world", "(h)ello", function(h)
    return string.upper(h) .. "i"
end)
print(result)  -- prints: Hi world

-- Pattern with magic characters
result = string.gsub("hello.world", "%.", "-")
print(result)  -- prints: hello-world


string.match(s, pattern, init?)

Returns the captures from the first match of pattern in string s.

Example:
-- Basic pattern matching
print(string.match("hello", "h"))  -- prints: h

-- Multiple captures
local year, month, day = string.match("2024-03-14", "(%d+)%-(%d+)%-(%d+)")
print(year, month, day)  -- prints: 2024 03 14

-- With init position
print(string.match("hello world", "(world)", 7))  -- prints: world

-- Pattern characters
print(string.match("123", "%d+"))      -- prints: 123
print(string.match("abc123", "%a+"))   -- prints: abc
print(string.match("   abc", "%s+"))   -- prints: "   "


string.gmatch(s, pattern)

Returns an iterator function that returns successive captures from pattern matches in string s.

Example:
local words = {}
for word in string.gmatch("hello world lua", "%w+") do
    table.insert(words, word)
end
print(words[1], words[2], words[3])  -- prints: hello world lua


string.len(s)

Returns the length of string s.

Example:
print(string.len("Hello"))  -- prints: 5


string.lower(s)

Returns a copy of s with all characters converted to lowercase.

Example:
print(string.lower("Hello"))  -- prints: hello


string.upper(s)

Returns a copy of s with all characters converted to uppercase.

Example:
print(string.upper("Hello"))  -- prints: HELLO


string.rep(s, n, sep?)

Returns a string that is the concatenation of n copies of string s.

Example:
print(string.rep("Hello", 3))  -- prints: HelloHelloHello


string.reverse(s)

Returns a string with the characters of s in reverse order.

Example:
print(string.reverse("hello"))  -- prints: olleh
print(string.reverse(""))       -- prints: "" (empty string)


string.sub(s, i, j?)

Returns the substring of s from position i to j.

Example:
print(string.sub("Hello", 2, 4))  -- prints: ell


string.split(s, sep)

Splits string s using separator sep and returns a table of substrings.

Example:
local parts = string.split("a,b,c", ",")
for i, part in ipairs(parts) do
    print(part)
end
-- Output:
-- a
-- b
-- c


Non-standard Extensions

string.startsWith(s, prefix)

Returns true if string s starts with prefix.

Example:
print(string.startsWith("hello world", "hello"))  -- prints: true
print(string.startsWith("hello world", "world"))  -- prints: false


string.endsWith(s, suffix)

Returns true if string s ends with suffix.

Example:
print(string.endsWith("hello world", "world"))  -- prints: true
print(string.endsWith("hello world", "hello"))  -- prints: false


string.trim(s)

Returns a copy of string s with whitespace removed from both ends.

Example:
print(string.trim("  hello  "))  -- prints: hello


string.trimStart(s)

Returns a copy of string s with whitespace removed from the beginning.

Example:
print(string.trimStart("  hello  "))  -- prints: hello 


string.trimEnd(s)

Returns a copy of string s with whitespace removed from the end.

Example:
print(string.trimEnd("  hello  "))  -- prints:   hello


string.matchRegex(s, pattern)

Matches string s against a JavaScript regular expression pattern and returns the result. This uses JavaScript's native regex capabilities rather than Lua patterns.

Example:
local match = string.matchRegex("hello123", "([a-z]+)([0-9]+)")
print(match[1], match[2])  -- prints: hello 123


string.matchRegexAll(s, pattern)

Returns an iterator that finds all matches of a JavaScript regular expression pattern in string s.

Example:
for match in string.matchRegexAll("a1b2c3", "([a-z])([0-9])") do
    print(match[0], match[1], match[2])  -- prints each full match and its capture groups
end
-- Output:
-- a1 a 1
-- b2 b 2
-- c3 c 3