User:OrenBochman/Lua Strings Advanced

Pattern Matching with Regular Expressions

Lua supports string matching using regualr expressions. Regular expressions are defined with the following symbols:

• ( - start group
• ) - end group
• . - any single character
• % - escape character
• + - 1 or more greedy
• * - 0 or more greedy
• - - 0 or more not greedy
• ? - 0 or one
• [ - start range
• ] - end range
• ^ - string start
• $ - string end

Character Classes

There are some predefined ranges:

• . - all characters
• %a - letters
• %l - lower case
• %u - upper case
• %d - digits
• %h - hexadecimal digits
• %w - alphanumeric characters
• %p - punctuation characters
• %s - whitespace
• %c - control characters

upper case version of these is the complement range.

s = "Deadline is 30/05/1999, firm"
date = "%d%d/%d%d/%d%d%d%d"
print(string.sub(s, string.find(s, date)))   --> 30/05/1999

print(string.gsub("hello, up-down!", "%A", ".")) --> hello..up.down. 4

here 4 is the count of substitutions returned by gsub

to count the number of Vowel in a string

dummy, nvow = string.gsub(text, "[AEIOUaeiou]", "")

where the dummy variable holds the vowel free string and nvow has the result.