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up vote 2 down vote favorite

I want to match a PHP regex string.

From what I know, they are always in the format (correct me if I am wrong):

/                 One opening forward slash
the expression    Any regular expression
/                 One closing forward slash
[imsxe]           Any number of the modifiers NOT REPEATING

My expression for this was:

^/.+/[imsxe]{0,5}$

Written as a PHP string, (with the open/close forward slash and escaped inner forward slashes) it is this:

$regex = '/^\/.+\/[imsxe]{0,5}$/';

which is:

^                 From the beginning
/                 Literal forward slash
.+                Any character, one or more
/                 Literal forward slash
[imsxe]{0,5}      Any of the chars i,m,s,x,e, 0-5 times (only 5 to choose from)
$                 Until the end

This works, however it allows repeating modifiers, i.e:

This: ^/.+/[imsxe]{0,5}$

Allows this: '/blah/ii'
Allows this: '/blah/eee'
Allows this: '/blah/eise'
etc...

When it should not.

I personally use RegexPal to test, because its free and simple.

If (in order to help me) you would like to do the same, click the link above (or visit http://regexpal.com), paste my expression in the top text box

^/.+/[imsxe]{0,5}$

Then paste my tests in the bottom textbox

/^[0-9]+$/i
/^[0-9]+$/m
/^[0-9]+$/s
/^[0-9]+$/x
/^[0-9]+$/e

/^[0-9]+$/ii
/^[0-9]+$/mm
/^[0-9]+$/ss
/^[0-9]+$/xx
/^[0-9]+$/ee

/^[0-9]+$/iei
/^[0-9]+$/mim
/^[0-9]+$/sis
/^[0-9]+$/xix
/^[0-9]+$/eie

ensure you click the second checkbox at the top where it says '^$ match at line breaks (m)' to enable the multi-line testing.

Thanks for the help

Edit

After reading comments about Regex often having different delimiters i.e

/[0-9]+/  == #[0-9]+#

This is not a problem and can be factored in to my regex solution.

All I really need to know is how to prevent duplicate characters!

Edit

This bit isn't so important but it provides context

The need for such a feature is simple...

I'm using jQuery UI MultiSelect Widget written by Eric Hynds.

Simple demo found here

Now In my application, I'm extending the plugin so that certain options popup a little menu on the right when hovered. The menu that pops up can be ANY html element.

I wanted multiple options to be able to show the same element. So my API works like this:

$('#select_element_id')
// Erics MultiSelect API
.multiselect({
    // MultiSelect options
})
// My API
.multiselect_side_pane({
    menus: [
        {
            // This means, when an option with value 'MENU_1' is hovered,
            // the element '#my_menu_1' will be shown. This makes attaching
            // menus to options REALLY SIMPLE
            menu_element: $('#my_menu_1'),
            target: ['MENU_1']
        },
        // However, lets say we have option value 'USER_ID_132', I need the
        // target name to be dynamic. What better way to be dynamic than regex?
        {
            menu_element: $('#user_details_box'),
            targets: ['USER_FORM', '/^USER_ID_[0-9]+$/'],
            onOpen: function(target)
            {
                // here the TARGET can be interrogated, and the correct
                // user info can be displayed

                // Target will be 'USER_FORM' or 'USER_ID_3' or 'USER_ID_234'
                // so if it is USER_FORM I can clear the form ready for input,
                // and if the target starts with 'USER_ID_', I can parse out
                // the user id, and display the correct user info!  
            }
        }
    ]
});

So as you can see, The whole reason I need to know if a string a regex, is so in the widget code, I can decide whether to treat the TARGET as a string (i.e. 'USER_FORM') or to treat the TARGET as an expression (i.e '/^USER_ID_[0-9]+$/' for USER_ID_234')

share|improve this question
    
regex patterns can use almost any delimiter. / seems to be very common but so is ~ and #. –  AbraCadaver Dec 12 '13 at 15:39
    
The '/^\/.+\/[imsxe]{0,5}$/' pattern does match: '/blah/eise', '/blah/eee' and '/blah/ii'. So i dont see the problem. All strings are beginning with a slash, contain a few characters followed by a slash and any of the characters 0-5 times. –  user202172 Dec 12 '13 at 15:44
    
Matching regexes is a difficult job. You might take a look at this answer. Also, there are more modifiers than the ones you specified, say for example U, so make sure to check this list. Also it might not be surprising if there was one not listed in there. Another issue, is if there is an escaped delimiter like /fail\/test/. TL;DR There's a lot to take into account ... –  HamZa Dec 12 '13 at 15:48
    
I'm terribly curious to know the use case driving this question... –  Alex Howansky Dec 12 '13 at 17:01
2  
From the PHP documentation: "...it is also possible to use bracket style delimiters where the opening and closing brackets are the starting and ending delimiter, respectively. {this is a pattern}" –  mcrumley Dec 13 '13 at 18:57

2 Answers 2

up vote 0 down vote

In order to prevent duplicate in modifier section, I'd do:

^/.+/(?:(?=[^i]*i[^i]*)?(?=[^m]*m[^m]*)?(?=[^s]*s[^s]*)?(?=[^x]*x[^x]*)?(?=[^e]*e[^e]*)?)?$
share|improve this answer
    
Your solution doesn't allow /^[0-9]+$/i as a valid expression! –  AlexMorley-Finch Dec 15 '13 at 15:48
up vote 1 down vote

Unfortunately, the regexp string can be "anything". The forward slashes you talk about can be a lot of characters. i.e. a hash (#) will also work.

Secondly, to match up to 5 characters without having them double could probably be done with lookahead / lookbehind etc, but will create such complex regexp that it's faster to post-process it.

It is possibly faster to search for the regular expression functions (preg_match, preg_replace etc.) in code to be able to deduct where regular expressions are used.

$var = '#placeholder#';

Is a valid regular expression in PHP, but doesn't have to be one, where:

const ESCAPECHAR = '#';
$var = 'text';
$regexp = ESCAPECHAR . $var . ESCAPECHAR;

Is also valid, but might not be seen as such.

share|improve this answer
    
Do you know how to prevent duplicate characters in the modifier section? P.s. read edits for context –  AlexMorley-Finch Dec 13 '13 at 11:27

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