[SOLVED] Little help with a regular expression

[Wolphie]

Hi,

  I'm totally new to regular expressions. So I'm looking for a bit of guidance and descriptions. My problem is that I'm trying to validate a name and description of a category for example, the name and description should only contain upper and lower case letters from A-Z and numbers from 0-9 with no special characters, not even an underscore. I also want to be able to limit the length of the string using regular expressions.

 

Here is what I have

if (!preg_match('[A-Za-z][A-Za-z0-9]{0,70}+', $str) {
// Error...
}

 

Could anybody provide any guidance and/or examples and a description of the operators used in regular expressions? e.g., + / *

 

Much appreciated, thanks.

 

[kratsg]

This will do the job. When you put "^" inside the box first like so, it's identical to a "NOT" operator. So if it finds a match that is NOT A-Za-z0-9, it will be true. Otherwise, no matches and it's false.

<?php
if(preg_match('/[^A-Za-z0-9]*/',$str)){
// Error
}
?>

 

The below code will produce identical results as well:

 

<?php
if(!preg_match('/[A-Za-z0-9]*/',$str)){
// Error
}
?>

 

The only difference is instead of using "^", I used "!" with the if/else statement.

 

Also note that the asterisk means to match zero or more times.

[JonnoTheDev]

Here is a description of your original regex:

Part 1: []

Match a single character in the range between A and Z

Match a single character in the range between a and z

Part 2: []

Match a character in the list below between 0 and 70 times, as many times as possible, without giving back (possessive)

Match a single character in the range between A and Z

Match a single character in the range between a and z

Match a single character in the range between 0 and 9

 

[Wolphie]

Thanks for the description both of you. It's much appreciated.

 

kratsg, do you have any advice about limiting the length of the string? Between 0 and 70 characters long?

 

Also, if possible could you explain what the "+", "/" and rules enclosed in braces and parenthesis is used for please?

 

Thanks.

[kratsg]

Here is a description of your original regex:

Part 1: []

Match a single character in the range between A and Z

Match a single character in the range between a and z

Part 2: []

Match a character in the list below between 0 and 70 times, as many times as possible, without giving back (possessive)

Match a single character in the range between A and Z

Match a single character in the range between a and z

Match a single character in the range between 0 and 9

 

 

Actually, that is false.

 

Match a character in the list below between 0 and 70 times, as many times as possible, without giving back (possessive)

 

(0,70) won't do that... however, {0,70} will. Anything inside parentheses is like brackets, except that you can use parentheses for backreferences in order to use preg_replace, etc...

 

Here's a quickie explanation:

 

\  the escape character - used to find an instance of a metacharacter like a period, brackets, etc.

. (period) match any character except newline

x match any instance of x

^x match any character except x

[x] match any instance of x in the bracketed range - [abxyz] will match any instance of a, b, x, y, or z

| (pipe) an OR operator - [x|y] will match an instance of x or y

() used to group sequences of characters or matches

{} used to define numeric quantifiers

{x} match must occur exactly x times

{x,} match must occur at least x times

{x,y} match must occur at least x times, but no more than y times

? preceding match is optional or one only, same as {0,1}

* find 0 or more of preceding match, same as {0,}

+ find 1 or more of preceding match, same as {1,}

^ match the beginning of the line

$ match the end of a line

 

 

Character Classes

\d  matches a digit, same as [0-9]

\D matches a non-digit, same as [^0-9]

\s matches a whitespace character (space, tab, newline, etc.)

\S matches a non-whitespace character

\w matches a word character

\W matches a non-word character

\b matches a word-boundary (NOTE: within a class, matches a backspace)

\B matches a non-wordboundary

[Wolphie]

Okay, I'm beginning to understand it a bit more now.

 

So, I'll try again based on my original rule..

if (preg_match('/[^A-Za-z\d]{0,70}/', $str) {
  // Error...
}

Would that do as I explained before? Or is "{0,70" still incorrect? If so, could you provide an example please?

[kratsg]

Are you only looking between 0 and 70 times? Then you can use:

 

'/[^A-Za-z\d]{0,70}/' for your pattern.

[Wolphie]

Yes, I only want to check that the length of the string is between 0 and 70 characters in length.

[kratsg]

That confused me:

 

Do you want to check to see if it is between 0 and 70 characters in length or do you only want to check 0-70 characters of that string?

 

To check length, use the strlen($str) function:

 

<?php

if(!strlen($str) <= 70){//error, it is not between 0 and 70 characters
} else {//no error, it is between 0 and 70 characters
}
?>

[JonnoTheDev]

Actually, that is false.

 

Look at the original regex that started the post off kratsg!

'[A-Za-z][A-Za-z0-9]{0,70}+'

[Wolphie]

Oh I know about strlen, but I just heard that you could check the length of the string using regular expressions. I guess you can only check how many iterations of the rule has been performed. Thanks, guys, this solved my problem and thanks for the detailed description kratsg. Thanks again neil.