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Lua Regular Expressions

Lua training course delegatesOK - don't believe the headline - Lua doesn't support "Regular expressions" but it does have pattern matching. Why? Because Lua is designed to have a small footprint, and a conventional Regular Expression library would be 'bloat' - the pattern matching that's provided looks similar, and offers 80% of the facilities in 20% of the code. (See the 80 / 20 rule).

You'll find an example of Lua pattern matching here in our courseware examples. A Lua pattern is a string that may include:

• Literal Characters to match exactly - e.g.
Letters, digits and many special chars match exactly
%% means really match a % character (similar for other specials)

• Character groups to match any one character from a group - e.g.
[aeiou] for a lower case vowel
%d means a digit
%a for a letter
%u for an upper case letter
%l for a lower case letter
%s for a space
%S for a non-space (and other capitalisations for opposite groups)

• Anchors to say if you're looking at the start or end of a string - e.g.
^ means "starting with"
$ means "ending with"

• Counts to say how many times to match the previous character - e.g.
+ means one or more of the previous item
? means zero or 0ne character
* means 0 or more or the previous item
- also means 0 or more of the previous item but is SPARSE

• Capture parenthesis to indicate interesting bits to save

There are some examples of iterating through a string to match patterns in Lua here.

Lua's pattern matching is covered on both our Learning to Program in Lua and Lua Programming courses. Illustration - on a private Lua course

(written 2009-08-28, updated 2010-06-19)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
U108 - Lua - Pattern matching
  [4366] Changing what operators do on objects - a comparison across different programming languages - (2014-12-26)
  [3687] Binary / bitwise operations in Lua with the standard bit32 library - (2012-04-06)
  [2727] Making a Lua program run more than 10 times faster - (2010-04-16)
  [2702] First and last match with Regular Expressions - (2010-04-02)
  [1847] Lua - IAQ (Infrequently Answered Questions) - (2008-10-18)
  [1744] Lua examples, Lua Courses - (2008-08-08)


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