Basic regexp help

I am new to programming PHP and am trying to validate a field in a form.

The field if for a RAL color code and so would look something like : RAL 1001. so the letters RAL and then 4 numbers.

Can someone help me set them into a regular expression to validate them. i have tried this with no success:

$string_exp = "/^[R开发者_C百科AL][0-9 .-]+$/i";

What can I say but sorry for being a complete NOOB at PHP.

Cheers Ben

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[RAL] will match just one character, either R, A or L, whereas you want to match the string "RAL". So you probably want something like this,

$string_exp = "/^RAL[0-9]{4}$/";

This will match "RAL1001", but not "RAL1","RAL 1001", "RAL12345", etc. If you wanted the space between RAL and the number, then also put that space into the regexp.

---

By removing redundant character classes, you'd get:

/^RAL \d{4}$/i

Note that using case-insensitive flag would make it match even such cases as Ral 1245 or raL 9875, for example.

---

/^RAL [0-9]{4}$/

If you enter letters as they are, they are found as they are. If you enclose something in [], it means: "Search a single character that is one of these."

Therefore starting with a literal "RAL " finds a literal "RAL " (or "ral ", too, when you apply the i flag).

---

Depends!

...
if( preg_match('/RAL\s*(\d{4})(?!\d)/', $name, $m) ) {
   echo $m[1];
}
...

This accepts 'someRAL 1234within text'
but doesn't accept 'RAL 12345'.

The exact regex depends entirely on your
context or specifications. You have to be more explicit in your question.