Constructing hard regular expressions with VerbalExpressions
Most newbie (and some seasoned) programmers have difficultly constructing Regular Expressions. Many a times one needs to create a Regexp quickly to test a a particular piece of code. However, not being comfortable withe Regexps can be a problem. VerbalExpressions is a PHP library that enables you to construct regular expressions using natural language like constructs. Think of it like a DSL for building Regexps.
Below is a sample PHP code that constructs a regular expression which tests whether a given string is a valid url.
<?php include_once('VerbalExpressions.php'); $regex = new VerEx; $regex ->startOfLine() ->then("http") ->maybe("s") ->then("://") ->maybe("www.") ->anythingBut(" ") ->endOfLine(); if($regex->test("http://www.codediesel.com")) echo "valid url"; else echo "invalid url"; ?> |
The main part of the code the DSL like interface that helps you build a Regexp.
$regex ->startOfLine() ->then("http") ->maybe("s") ->then("://") ->maybe("www.") ->anythingBut(" ") ->endOfLine(); |
If you want to see what regular expression the code has built, we can use the getRegex function of the class.
<?php include_once('VerbalExpressions.php'); $regex = new VerEx; $regex ->startOfLine() ->then("http") ->maybe("s") ->then("://") ->maybe("www.") ->anythingBut(" ") ->endOfLine(); echo $regex->getRegex(); |
This will print the Regexp given below.
/^(http)(s)?(\:\/\/)(www\.)?([^ ]*)$/m |
We can now use the above Regexp in our code to accomplish the same thing as above.
$myRegexp = '/^(http)(s)?(\:\/\/)(www\.)?([^ ]*)$/m'; if (preg_match($myRegexp, 'http://www.codediesel.com')) { echo 'valid url'; } else { echo 'invalud url'; } |
We can also use the $regex object given in the above example directly in our code where the particular Regexp is required.
include_once('VerbalExpressions.php'); $regex = new VerEx; $regex ->startOfLine() ->then("http") ->maybe("s") ->then("://") ->maybe("www.") ->anythingBut(" ") ->endOfLine(); if (preg_match($regex, 'http://www.codediesel.com')) { echo 'valid url'; } else { echo 'invalud url'; } |
The PHP version of VerbalExpressions is a port of the original JavaScript version, JSVerbalExpressions. Additional modifiers that will help you build regular expressions can be found here.
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3 Responses
1
Steven Wade
August 14th, 2013 at 10:14 am
Great article! VerbalExpressions is a great library and helps me out a lot.
I built a little GUI that uses the JS version the library to help build regular expressions.
http://buildregex.com
2
一种更符合自然语意的PHP正则表达式
August 15th, 2013 at 7:10 am
[…] 文章节选：constructing-hard-regular-expressions-with-verbalexpressions […]
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PHP Digest №1 ( 11.08.2013 — 25.08.2013 ) | FASIGN Blog
August 28th, 2013 at 10:40 am
[…] Reguläre Ausrücke mit hilfe von VerbalExpressions bauen — VerbalExpressions ist eine PHP-Lib, mit der man Reguläre ausdrücke mit einfacher Sprache zusammenstellen kann ohne sich im RegEx auszukennen. z.B. um eine URL zu matchen: $regex->startOfLine()->then("http")->maybe("s")->then("://")->maybe("www.") ->anythingBut(" ")->endOfLine(); […]