UnicodeRegexMatch (Unicode function): Difference between revisions

Revision as of 17:59, 12 May 2016

Position after match of regex (Unicode class)

The UnicodeRegexMatch intrinsic function determines whether a given pattern (regular expression, or "regex") matches within a given string according to the rules of regular expression matching.

Syntax

%number = unicode:UnicodeRegexMatch( regex, [Options= string], - [CaptureList= stringlist]) Throws InvalidRegex

Syntax terms

%number A variable to return the position of the character after the last character matched, or a zero if no characters in the method object Unicode string match the regular expression.

unicode The input Unicode string, to which the regular expression regex is applied.

regex A Unicode string that is interpreted as a regular expression and that is applied to the method object unicode to determine whether the regular expression matches unicode.

Options

This is an optional, but name required, parameter supplying a string of single-letter options, which may be specified in uppercase or lowercase, in any combination, and blank-separated or not as you prefer. For more information about these options, see Common regex options.

`I`	Do case-insensitive matching between `unicode` and `regex`.
`S`	Dot-All mode: a period (`.`) can match any character, including carriage return and linefeed.
`M`	Multi-line mode: let anchor characters match end-of-line indicators *wherever* the indicator appears in `unicode`. `M` mode is ignored if `C` (XML Schema) mode is specified.
`C`	Do the match according to XML Schema regex rules. Each `regex` is implicitly anchored at the beginning and end, and no characters serve as anchors.

CaptureList This argument is available for Rocket development testing purposes only. It is not an ordinary user parameter.

Usage notes

It is strongly recommended that you protect your environment from regular expression processing demands on PDL and STBL space by setting, say, UTABLE LPDLST 3000 and UTABLE LSTBL 9000. See SOUL programming considerations.
For information about additional methods that support regular expressions, see Regex processing.
UnicodeRegexMatch may be something of a misnomer. It does not determine if a string matches a regular expression, it determines if a string contains a substring that matches a regular expression. UnicodeRegexMatch behaves more like a matching method if the regular expression is "anchored" (begins with a caret (^) and ends with a dollar sign ($)), or if the C option indicates XML Schema mode.

Examples

Finding the first position of one of several characters

A common programming problem is to "scan" a string and find the first position that is one of several characters. This can be readily accomplished with UnicodeRegexMatch. Here is an example:

... %regexU = '[aeiou]'; * Scan for any lowercase vowel %strU = 'At the centre of it all, your eyes' %iU = %str:unicodeRegexMatch(%regexU) if %iU then printText Before vowel: {%strU:unicodeLeft(%i - 2)} printText The vowel: {%strU:unicodeChar(%i-1)} printText After vowel: {%strU:unicodeSubstring(%i)} ...

The result of the above fragment is:

Before vowel: At th The vowel: e After vowel: centre of it all, your eyes

Notes:

The position returned by UnicodeRegexMatch is the position of the character after the first successful match.

Finding the first position that is not one of several characters

A programming task similar to that in the preceding example is finding the position of the first character that is not one of a set of characters. This task is readily accomplished with UnicodeRegexMatch. Here is an example:

%regex = '[^aeiou]'; * Scan for any non-vowel %str = 'albatross' %i = %str:unicodeRegexMatch(%regex) if %i then printText Before non-vowel: {%str:unicodeLeft(%i - 2)} printText The non-vowel: {%str:unicodeChar(%i-1)} printText After non-vowel: {%str:unicodeSubstring(%i)}