regexp searches text using Perl-compatible regular expressions.

A regular expression describes a pattern rather than a literal string. Use it when the text can vary, for example when matching identifiers, dates, email addresses, numbers, tags, or alternative spellings.

A typical workflow is to identify the pieces of text that are unique, translate each piece into regular expression syntax, and then call regexp with the output key that returns the information you need.

By default, regexp returns 1-based start indices for every non-overlapping match. Matching continues after the end of the previous match. Use the 'once' option to stop after the first match.

Common metacharacters:

Pattern	Meaning	Example
.	any character	'a.c' matches 'abc' and 'axc'
[abc]	one character from a set	'[ch]at' matches 'cat' or 'hat'
[^abc]	one character not in a set	'[^0-9]' matches a non-digit character
[a-z]	one character in a range	'[A-Z]+' matches uppercase letters
\w, \W	word or non-word character	'\w+' matches words and identifiers
\d, \D	digit or non-digit character	'\d{4}' matches four digits
\s, \S	white-space or non-white-space character	'\w+\s+\w+' matches two words separated by spaces

Quantifiers specify how many times the preceding expression can occur.

Pattern	Meaning
expr*	zero or more times
expr+	one or more times
expr?	zero or one time
expr{m,n}	at least m and at most n times
expr{m,}	at least m times
expr{n}	exactly n times

Quantifiers are greedy by default. Add ? after a quantifier for a lazy match, such as '.*?' . Add + after a quantifier for a possessive match, such as '.*+' .

Grouping operators control tokens and alternatives.

Pattern	Meaning
(expr)	group and capture a token
(?:expr)	group without capturing a token
(?<name>expr)	capture a named token
(expr1|expr2)	match either expression
\1, \2, ...	match the same text as a previously captured token

Anchors and assertions match positions rather than characters.

Pattern	Meaning
^, $	beginning and end of the input text, or of a line with 'lineanchors'
\<, \>	beginning and end of a word
\b, \B	word boundary or not a word boundary
(?=expr), (?!expr)	positive or negative lookahead
(?<=expr), (?<!expr)	positive or negative lookbehind

Use 'ignorecase' for case-insensitive matching, 'dotexceptnewline' when . must not match newline characters, 'lineanchors' when ^ and $ should apply to individual lines, and 'forceCellOutput' to force scalar text results into cells.

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