r - Regular Expression Builder (PHP)

r Is a PHP library to build regular expressions.

It is written for PHP 5 and it handles PCRE patterns in a fairly advanced level, but it does not cover the complete specification.

Why?

There are several reasons why one would want build a regular expression with code, rather than to write it down directly:

* For non-experts, the expression is easier to read * It is a handy tool to compose an expression at runtime, depending on different variables and rules * There is no need to escape characters, which is always a tricky part * No need to look up the syntax of little used constructs: the fluid interface allows for auto completion

Examples

These examples can also be found in the file 'examples.php'.

Full string match

/^Paradise Lost$/

R::expression()
	->startOfString()
	->text('Paradise Lost')
	->endOfString()

Alternate texts

/The (dog|cat)?basket fell off the roof/

R::expression()
	->text('The ')
	->group(
		R::group()->optional()->oneOfThese()->text('dog')->text('cat')
	)
	->text('basket fell off the roof')

Characters

/the [bc]?old man and the [^c]ee.*/

R::expression()
	->text('the ')
	->inChars(R::chars('bc')->optional())
	->text('old man and the ')
	->notInChars(R::chars('c'))
	->text('ee')
	->char(R::anyChar()->zeroOrMore())

Nested groups

/(<a href='([^']*)'>)/

R::expression()
	->group(
		R::group()
			->text("<a href='")
			->group(
				R::group()
					->notInChars(R::chars("'")->zeroOrMore())
			)
			->text("'>")
	)

Assertions

/\bkettle\b/

R::expression()
	->wordBoundary()
	->text('kettle')
	->wordBoundary()

Quantifiers

/[\d]{4}[a-z]{2}/

R::expression()
	->char(R::chars()->digit()->times(4))
	->char(R::chars()->letter()->times(2))

Named blocks, alternate delimiters (#)

#(?P<protocol>http[s]?)://(?P<url>.*)#

R::expression()
	->group(
		R::group('protocol')
			->text('http')
			->char(R::chars('s')->optional())
	)
	->text('://')
	->group(
		R::group('url')
			->char(R::anyChar()->zeroOrMore())
	)

Multiline expression

/^start\s+(^the)\s+show$/m

R::multiLineExpression()
	->startOfStringOrLine()
	->text('start')
	->whitespace()
	->group(
		R::group()->startOfLine()->text('the')
	)
	->whitespace()
	->text('show')
	->endOfStringOrLine()

Look behind, look ahead

/(?<=Lord )(Byron)/

R::expression()
    ->lookBehind(
        R::lookBehind()->text('Lord ')
    )
    ->group(
        R::group()->text('Byron')
    )

The old way is way easier!

Then write parts of the expression in the old style:

#(?P<protocol>https?)://(?P<url>.*)#

R::expression()
	->group(
		R::group('protocol')->raw('https?')
	)
	->text('://')
	->group(
		R::group('url')->raw('.*')
	)

Credits

The credits for the idea of creating a regular expression builder go to VerbalExpressions. It is a fascinating idea and I wanted to see how far it could go. I chose a different type of implementation based on nested fluid interface calls.