string.sub()

The string.sub() function in Lua extracts a substring from a given string. It allows you to specify the starting and optionally the ending positions for the substring. This function is useful for string manipulation and text processing.

Syntax

string.sub(s, start, end_)

Parameters

Name
s
Type
string
Description
The string from which to extract the substring.
Name
start
Type
number
Description
The starting position of the substring (1-based index).
Name
end_
Type
number
Description
The ending position of the substring (1-based index). If omitted, the substring will extend to the end of the string.

Return Value

Returns the extracted substring. If the starting position is greater than the length of the string, an empty string is returned. If the ending position is less than the starting position, it also returns an empty string.

Examples

Example 1: Extracting a Substring

Extract a simple substring from a string.

Example 1

local substring = string.sub("Hello, World!", 1, 5)
print(substring)  -- Output: Hello

Example 2: Omitting the Ending Position

Extract a substring from the starting position to the end of the string.

Example 2

local substring = string.sub("Lua Programming", 5)
print(substring)  -- Output: Programming

Example 3: Negative Indexing

Using negative indices to count from the end of the string.

Example 3

local substring = string.sub("Hello, World!", -6, -1)
print(substring)  -- Output: World!

Example 4: Invalid Indices

Demonstrate behavior with invalid indices.

Example 4

local invalid = string.sub("Hello", 10)
print(invalid)  -- Output: (empty string)

local empty = string.sub("Hello", 3, 2)
print(empty)  -- Output: (empty string)

Use Cases

String Manipulation: Extracting specific parts of strings for analysis or display.
Data Processing: Useful in scenarios where only certain portions of a string are needed, such as parsing or formatting.