Lua Coding Docs: String Patterns

String Patterns

Matching Patterns are patterns used to match character combinations to get the specific output. This is used for searching, matching, verifying the text data and replacing characters in strings. Some String Methods support Matching Patterns that allow you to pass Matching Patterns as its arguments.

This is an replacement for Regular Expressions (RegEx) because the primary cause of this is size. More than 4,000 lines of code are typically required for a RegEx implementation. This exceeds the combined size of all Lua standard libraries. In contrast, Lua's pattern matching implementation comprises fewer than 500 lines.

Special Sequences

Special Sequence are characters used to represent a group of specific characters that can be used by the pattern to match the desired character. For example, the character class %p matches any punctuation characters so we can use this for. To manipulate the punctuation characters to whatever we want.

Characters	Description	Matched Results
%a	Matches any Alphabetical Characters	AaBbCcDd
%w	Matches any Alphanumeric Characters	AaBb0123
%d	Matches any Numeric Characters	01234567
%l	Matches any Lower-case Characters	aabbccdd
%u	Matches any Upper-case Characters	AABBCCDD
%p	Matches any Punctuation Characters	!@#$%;,.
%x	Matches any Hexadecimal Characters	0123456789AaBbCcDdEeFf
%s	Matches any White Space Characters	Space, New Line, Tab, etc
%c	Matches any Control Characters	Carriage Return, Escape, Delete, etc

Example:

function onCreatePost()
     setTextString('scoreTxt', 'Score: 0 | Misses: 0 | Accuracy: ?')
end

local scorePattern1 = '%d+%p+%d+%%'  -- Checks the accuracy is a float | '%d+%p+%d+%%' > '99.45%'
local scorePattern2 = '%d+%%'        -- Checks the accuracy is a int   | '%d+%%' > '100%'
function onUpdateScore(miss)
     local scoreTxt = getTextString('scoreTxt')
     local scoreTxtDisplay1 = 'Score: '..getScore()..' | Misses: '..miss..' | Accuracy: '
     local scoreTxtDisplay2 = (scoreTxt:match(scorePattern1) or scoreTxt:match(scorePattern2))
     setTextString('scoreTxt', scoreTxtDisplay1..scoreTxtDisplay2..' ['..ratingFC..']')
end

Meta Characters

Meta Characters are modifiers for special sequences that extend their meaning. For instance, the plus + character will be assigned to the special sequences with the longest chain it could discover. Another example you could use the caret ^ character to get the specific starting pattern inside a string.

Characters	Description	Example
.	Matches any characters.	H...o
$

Repetition

Characters	Description
+	Matches one or more characters; will match the longest possible chain.
*	Matches zero or more characters; will match the longest possible chain.
-	Matches zero or more characters; will match the shortest possible chain.
?	Matches zero or one character.

Example:

function onCreate()
     debugPrint(('Score: 892344'):match('%d+')) -- will print > 892344
     debugPrint(('Change'):match('Changes?'))   -- will print > 'Change'
end

Anchors

Characters	Description
^	Forcefully matches any character(s) at the start of a line; must be placed behind.
$	Forcefully matches any character(s) at the end of a line; must be placed in front.

Example:

function onCreate()
     debugPrint(('icon-foo'):match('^icon%-'))        -- will print > 'icon-'
     debugPrint(('icon-foo-pixel'):match('%-pixel$')) -- will print > '-pixel'
end

Sets

Characters	Description
[set]	Matches any specific individual of characters that it could find.
[^set]	Matches every character except the ones inside the sets.
[min-max]	Matches any specific range of characters that it could find.
[^min-max]	Matches every character except the ones inside the range sets.

Example:

function gcheckPattern(str, ptr)
     local result = {}
     for words in (str):gmatch(ptr) do -- does an epic global matching
          table.insert(result, words)
     end
     return tostring(#result)..' patterns found!'
end

local gooberWord = 'pneumonoultramicroscopicsilicovolcanoconiosis' -- this is a real word
function onCreate()
     debugPrint(gcheckPattern(gooberWord, '[aeiou]'))  -- will print > '20 patterns found!'
     debugPrint(gcheckPattern(gooberWord, '[^aeiou]')) -- will print > '25 patterns found!'
     debugPrint(gcheckPattern(gooberWord, '[a-r]'))    -- will print > '37 patterns found!'
     debugPrint(gcheckPattern(gooberWord, '[^b-p]'))   -- will print > '12 patterns found!'
end

Captures

Captures is a collection of captured strings for a single match that excludes other characters from the outside, this use the parenthesis () characters.

Example:

local support = 'I love the "RGB" Community!'
function onCreate()
     debugPrint((support):match('"(RGB)"')) -- will print > 'RGB'
     debugPrint((support):match('"RGB"'))   -- will print > '"RGB"'
end