Home arrow FAQ arrow Q1 Frequently Asked Questions arrow Regular expressions
Apr 24, 2017 at 12:24 AM
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Regular expressions

Q1 allows the use of regular expressions in most of the places where a string comparison is required (for example when searching a list item by name or a window by its title). You can specify you want to use a regular expression match by prefixing the pattern with the backslash character (\). Note that the syntax of some script languages (for example JScript) allows backslash characters in strings only if they are escaped by a second backslash ("\\" = "\").

// This will search for an item whose value equals 'a*b'
var item1 = listbox.findItem("a*b");

// This will search for an item whose value equals 'b', 'ab', 'aab' and so on
var item2 = listbox.findItem("\\a*b");
		

Syntax

Regular expressions allow a great deal of flexibility when working with strings, but it may take some time to get used to their syntax, that is if they are not already familiar to you.

A regular expression pattern describes how a string should look in order to be considered a valid match. It is composed of string literals (letters and numbers) together with escape characters which define matching rules: 

  • '.' (dot character) matches any single character.

  • '*' placed after an expression matches the expression repeated zero or more times. For example 'ba*' will match 'b', 'ba', 'baa' and so on. The pattern '.*' will match any number of any characters.

  • '+' behaves like '*' but the expression has to appear at least once.

  • '?' allows an expression to appear zero or one times.

  • '{min,max}' allows an expression to be repeated at least min times but no more than max times. For example 'a{1,3}' matches 'a', 'aa' and 'aaa', 'a{2,}' matches the character 'a' repeated at least two times and 'a{2}' matches 'aa'.

  • '()' treats the expression within parenthesis as a group and all modifiers apply to the whole group. For example '(abc)*' will match 'abc', 'abcabc' and so on.

  • '|' matches either the expression on the left of | or the one on the right. For example 'abc|xyz' matches either 'abc' or 'xyz'.

  • '[]' matches a character belonging to the set specified within the sqare brackets. Sets can be defined as follows:

    • [abc] will match one character which can be either 'a', 'b' or 'c'.
    • [a-z] will match one character between 'a' and 'z'.
    • [^abcX-Z] will match any one character which is not 'a', 'b', 'c', 'X', 'Y' or 'Z'.
  • '^' matches the beginning of a line.

  • '$' matches the end of a line.

  • '\<' matches the beginning of a word.

  • '\>' matches the end of a word.

  • '\x{code}' allows to specify a character by its hexadecimal code.

  • '[[:class:]]' allows to specify a character by its class. Available classes are:

    • [[:alnum:]] Alphanumeric characters.
    • [[:alpha:]] Alphabetical character (a-z and A-Z).
    • [[:blank:]] Blank character (spaces or tabs).
    • [[:digit:]] Digits (0-9).
    • [[:lower:]] Lower case characters (a-z).
    • [[:punct:]] Punctuation characters.
    • [[:space:]] Whitespace characters.
    • [[:upper:]] Upper case characters (A-Z).
    • [[:xdigit:]] Hexadecimal digit characters (0-9, a-f and A-F).
    • [[:word:]] Word characters (alphanumeric characters plus '_').
    • [[:unicode:]] Character whose code is greater than 255.
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