Lesson 43 of 55
8 mins readThe string Library: sub, byte, rep & Case
In Plain English
The built-in `string` library provides functions for slicing, byte conversions, case normalization, and formatting. Functions can be called as `string.fn(s)` or via method syntax `s:fn()`.
Deep Dive: How It Works
Method Calling Syntax: All strings have a metatable with `__index = string`, enabling `"hello":upper()`.
string.sub(s, start, end): Extracts substring using 1-based indices (supports negative indices).
string.rep(s, n): Repeats string `n` times.
string.byte / string.char: Converts between characters and ASCII/Unicode byte codes.
Core Rules to Remember
String Method Syntax: Call `s:upper()` or `s:sub(1, 4)` directly on any string.
Negative Indexing: `s:sub(-3)` extracts the last 3 characters.
Live Interactive Example
Hit Run Code to see it liveString Transformations
Python 3.12
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Output Console
Click "Run Code" to view the rendered output.
How it works: text:sub pulled slices and string.rep repeated the divider line.
Your Turn: Micro Challenge
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Micro Exercise
Extract Substring Prefix
- Declare `local code = "PROD-9874"`.
- Extract the first 4 characters `local env = code:sub(1, 4)`.
- Print `"Environment: " .. env`.
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Sandbox Output
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