Basic Regular Expression Syntax

A regular expression defines a text (i.e. character string) pattern and assigns a variable to each component of the pattern.

The basic rules for patterns are:

• ^ Beginning of string
• $ End of string
• . Any character
• [ Start of character list
• ] End of character list
• ( Start of expression group
• ) End of expression group
• | ORs two expressions
• \ Escape character
• * Preceding expression occurs zero or more times *? Preceding expression occurs zero or one times
• + Preceding expression occurs one or more times
• all other characters match themselves

The [ and ] characters can enclose character lists:

• [ab] denotes a single lowercase a or b letter
• [a-z] any lowercase letter
• [0-9] any digit
• [0-9]+ any number
• [a-z,A-Z,0-9] any letter or digit

Examples:

• .* denotes any sequence of characters

• .* .* denotes any string of characters that includes a space

• You use “capture groups” to determine which parts of the text will be grouped together and put into a variable. You achieve this grouping by placing brackets around the capture group:

• (.*) (.*) creates two capture groups $1 and $2; $1 will contain all characters before the space and $2 will contain all characters after the space

• As mentioned before the different capture groups will be placed into capture variables. These variables are denoted by $1, $2, $3, $4, etc.. $0 is a special variable that holds the entire matched pattern.

Please note that the old style \1, \2, \3, etc. capture variables syntax is still supported in the Re-arrange using regular expressions action for backwards compatibility reasons, but we recommend using the now standard $1, $2, $3, etc. syntax instead.

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