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Lua string patterns Cheat Sheet by

Reference to Lua string matching patterns

Function Calls


string.find(string, pattern, startindex, nopattern)   # returns indices
string.gmatch(string, pattern, startindex)            # creates a iterator returning all matches
string.match(string, pattern, startindex)             # returns the matched string
string.gsub(string, pattern, replace)                 # replace can be a function or table, can use %n to use n-th captured element

Pattern Syntax

A pattern is a list of consec­utive pattern items.
Adding a 
^
at the start of a pattern anchors it to the start of the string, and 
$
at the end. Otherwise, they have no special meaning.

Character Classes

x
Represents 
x
, where is is not 
^$()%.[­]*+-?
 
%x
Represents 
x
where 
x
can be anything
 
%l
Lowercase letters
 
%u
Uppercase characters (same as 
%L
)
 
%d
Digits
 
%x
Hexade­cimal digits (same as 
[a-fA-­F0-9]
 
%w
Alphan­umeric characters (same as 
[a-Z0-9]
)
 
%a
Everything
 
%s
Space characters
 
%p
Punctu­ation characters
 
%g
Printable characters (not including space)
 
%c
Control characters
 
[set]
Union of all characters in the set, with possible character classes and RegEx style ranges
 
[^set]
Inverse of 
[set]
The uppercase variant represents the inverse of the set, so 
%L
represents 
%u
.
The dash can be included in sets by positi­oning it as the first or last character, and the square bracket as the first. Or just use a escape.
  

Pattern Item

A pattern item can be any of the following:
Character Class
1 of the class
Character Class with *
≥0 of the class, longest possible
Character Class with -
≥0 of the class, shortest possible
Character Class with +
≥1 of the class
Character Class with ?
1 | 0 of the class
 
%n
Matches the n-th captured string
 
%f[set]
Frontier pattern
 
%bxy
Balanced match
Frontier patterns ::: They match an empty string 
"­"
that does not precede with the set, but does succeed with the set.
Balanced match ::: They match until the pair balances out. For example, 
%(>
matches entirely 
(The quick br((own f>ox jum>ped over the lazy dog>
.

Captures

Captures allow you specify groups. They are defined with parent­heses, and they can include any valid pattern within.

Using pattern reference we can match the same character. Note that it is not reusing the pattern, it is reusing what the pattern matched. 
([abcd])%1
is NOT the same as 
[abcd]­[abcd]
.

You can also use captures to return results from 
string.find
after the indices, multiple results in 
string.gmatch
and 
string.match
, and use in the replac­ement string in 
string.gsub
.

The empty capture 
()
represents the current index in the string.
               
 

Metadata

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  • Published: 5th November, 2023

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