| Regular Expressions

## Regular Expressions in SciTE

### Purpose

Regular expressions can be used for searching for patterns rather than literals. For example, it is possible to search for variables in SciTE property files, which look like $(name) with the regular expression:
\$([a-z.]+)

Replacement with regular expressions allows complex transformations with the use of tagged expressions. For example, pairs of numbers separated by a ',' could be reordered by replacing the regular expression:
\([0-9]+\),\([0-9]+\)
with:
\2,\1

### Syntax

1. char matches itself, unless it is a special character (metachar): . \ [ ] * + ^ $
2. . matches any character.
3. \ matches the character following it, except when followed by a left or right round bracket, a digit 1 to 9, one of the characters abfnrtv, or a left or right angle bracket. (see [7], [8] and [9]) It is used as an escape character for all other meta-characters, and itself. When used in a set ([4]), it is treated as an ordinary character.
4. [set] matches one of the characters in the set. If the first character in the set is "^", it matches a character NOT in the set, i.e. complements the set. A shorthand S-E is used to specify a set of characters S up to E, inclusive. The special characters "]" and "-" have no special meaning if they appear as the first chars in the set. examples: match: [a-z] any lowercase alpha [^]-] any char except ] and - [^A-Z] any char except uppercase alpha [a-zA-Z] any alpha
5. * any regular expression form [1] to [4], followed by closure char (*) matches zero or more matches of that form.
6. + same as [5], except it matches one or more.
7. a regular expression in the form [1] to [10], enclosed as \(form\) matches what form matches. The enclosure creates a set of tags, used for [8] and for pattern substitution. The tagged forms are numbered starting from 1.
8. a \ followed by a digit 1 to 9 matches whatever a previously tagged regular expression ([7]) matched.
9. a \ followed by one of the characters abftv is a control character. \a is BEL, \b is BS, \f is FF, \t is TAB, and \v is VT.
10. \< a regular expression starting with a \< construct \> and/or ending with a \> construct, restricts the pattern matching to the beginning of a word, and/or the end of a word. A word is defined to be a character string beginning and/or ending with the characters A-Z a-z 0-9 and _. It must also be preceded and/or followed by any character outside those mentioned.
11. a composite regular expression xy where x and y are in the form [1] to [10] matches the longest match of x followed by a match for y.
12. ^ a regular expression starting with a ^ character $ and/or ending with a $ character, restricts the pattern matching to the beginning of the line, or the end of line. [anchors] Elsewhere in the pattern, ^ and $ are treated as ordinary characters.

### Acknowledgments

Most of this documentation was originally written by Ozan S. Yigit.
Additions by Neil Hodgson.
All of this document is in the public domain.