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Text Functions Using Regular Expressions

G2 provides various system-defined functions that find and/or replace text as designated by numeric arguments and regular expressions. For brevity, the names of such functions call a regular expression a pattern.

Text functions in general are described under G2 Text Manipulation Functions and G2 Conventions for Manipulating Text. G2 functions in general are described in Chapter 25, Functions.

Locating a Substring Using a Regular Expression

find-next-pattern 
	(search-pattern: text, source-text: text, start-position: integer) 
	-> 	structure (start-index: integer, end-index: integer)

Searches through source-text, starting at start-position, for a substring that matches search-pattern, a regular expression, and returns a structure containing the start-index and end-index of the match, or:

structure (start-index: 0, end-index: 0)

if no match exists. Examples:

find-next-pattern ("{A-Z}{a-z}*", "according to Will Rogers", 1)
-> structure (start-index: 14, end-index: 17)

Many substrings match the pattern. "W", "Wi", "Wil", and "Will" begin at position 14, and "R", "Ro", etc., begin at position 19. The function returns the start and end positions of the leftmost longest matching substring.

find-next-pattern ("{A-Z}{a-z}*", "according to Will Rogers", 15)
-> structure (start-index: 19, end-index: 24)

"Will" is not a candidate, because the search starts at position 15. The function therefore returns the start and the end positions of "Rogers".

Extracting a Substring Using a Regular Expression

find-next-substring-matching-pattern 
	(search-pattern: text, source-text: text, start-position: integer)
	-> 	substring: text

Identical to find-next-pattern, except that the function returns the matching substring itself, rather than the substring's start and end positions. If no match exists, the function returns the empty string (*"). Example:

find-next-substring-matching-pattern 
("{A-Z}{a-z}*", "according to Will Rogers", 1)
-> "Will"

Replacing a Substring Using a Regular Expression

find-and-replace-pattern 
	(search-pattern: text, text-to-substitute: text, source-text: text, 
	 start-position: integer, end-position: integer)
	-> 	modified-text: text

Replaces each occurrence of search-pattern, a regular expression, in source-text between start-position and end-position, with text-to-substitute, a text string, and returns the complete source-text with the changes made. After each replacement, the search continues from the first character unaffected by the change. Example:

find-and-replace-pattern ("abcd", "cdab", "abcdcdef", 1, 8)
-> "ababcdef"

If no substring between start-position and end-position matches search-pattern, the function returns source-text unchanged.

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Text Functions Using Regular Expressions

Locating a Substring Using a Regular Expression

Extracting a Substring Using a Regular Expression

Replacing a Substring Using a Regular Expression

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