Regex pattern in JSON?

Question

I'm trying to have a single JSON file to validate data both in front (JS) and back (PHP). I cannot figure out how to have my pattern in a json string, PHP won't convert it. Here's what I'd like to use (email validation):

'{"name":"email", "pattern":"^[a-z0-9]+(\.[_a-z0-9]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,15})$"}'

I suppose there's something in pattern that doesn't get treated as a string? This as it is, won't convert to an object in PHP. I shouldn't have to escape anything but I might be wrong...

thanks

Edit: Tried this as suggested in comments:

json_decode('{"name":"email", "pattern":"^[a-z0-9]+(\\.[_a-z0-9]+)*@[a-z0-9-]+(\\.[a-z0-9-]+)*(\\.[a-z]{2,15})$"}‌​');  ==> NULL

Solution

The problem are the backslashes \. Use two to signal that there is one and it will work well:

{"name":"email","pattern":"^[a-z0-9]+(\\.[_a-z0-9]+)*@[a-z0-9-]+(\\.[a-z0-9-]+)*(\\.[a-z]{2,15})$"}

---

The above is valid JSON but will cause trouble as PHP string, because \\ will already be interpreted as one \ before it is passed to json_decode(), and we're back where we started from. As deceze kindly pointed out in the comments, this can be solved by adding four backslashes:

{"name":"email","pattern":"^[a-z0-9]+(\\\\.[_a-z0-9]+)*@[a-z0-9-]+(\\\\.[a-z0-9-]+)*(\\\\.[a-z]{2,15})$"}

Or by immediately passing the contents from file_get_contents() (or similar) to json_decode().

Comments

[Eric]

There must be something else, I've tried that too. Still won't parse

[Eric]

json_decode('{"name":"email", "pattern":"^[a-z0-9]+(\\.[_a-z0-9]+)*@[a-z0-9-]+(\\.[a-z0-9-‌​]+)*(\\.[a-z]{2,15})‌​$"}'); ==> NULL

[Gromski]

@Eric If you're writing it as a PHP string literal (as opposed to reading it from a file, for example) you'll need an additional backslash for each backslash.

[Eric]

Do you mean triple backslash for a backslash ?

[ljacqu]

Indeed, \ has to be \\\\ in PHP. {"name":"email","pattern":"^[a-z0-9]+(\\\\.[_a-z0-9]+)*@[a-z‌​0-9-]+(\\\\.[a-z0-9-‌​]+)*(\\\\.[a-z]{2,15‌​})$"} works. But the one in my post is valid JSON. I'll do a test with JavaScript and I'll update my post in a bit.

[Gromski]

@Eric Quadruple backslash for each backslash. Tip: write the plain regex into a file, then: var_export(json_encode(array('pattern' => file_get_contents('regex.txt')))); This'll "reverse engineer" the valid syntax.

[ljacqu]

Thanks for the comments @deceze, I hope it's OK that I've linked to your profile in my update.