php preg_match or preg_replace to validate

Question

I want to check a string to allow only a-z A-Z 0-9 . / ? & but I'm unsure how exactly to use preg_match().

If you could also explain what each part of the code is I'd appreciate it! (ie why do you add /^ and how to you add a /)

Thanks

ioseb · Accepted Answer · 2012-06-15 08:01:55Z

4

Here it is:

$input = 'Hello...?World';
$regex = '~^[a-z0-9&./?]+$~i';

if (preg_match($regex, $input)) {
  echo "yeah!";
}

You can build your own character classes and validate strings this way.

Explanation:

~
^                        # string start
[                        # start character class 
  a-z                    # letters from a to z
  0-9                    # digits from 0 to 9
  &./?                   # &,.,/ and ? chars
]                        # end character class
+                        # repeat one or more time
$                        # string end
~ix

edited Jun 15, 2012 at 8:01

answered Jun 15, 2012 at 7:56

ioseb

17k3 gold badges37 silver badges31 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

DaveRandom Over a year ago

.?/ are not meta characters in a character class and do not need escaping. / is not a meta character anyway, it only needs escaping if you use it as a delimiter. Every character has its literal meaning except ]\^- Also you would be better to do if (!preg_match('~[^a-z0-9&./?]~i')) for simplicity and to give PCRE less to do, I feel.

xiankai · Accepted Answer · 2012-06-15 08:23:01Z

-1

if ( preg_match('[^a-zA-Z0-9./?&]', 'azAZ09./?&') ) {
     //found a character that does not match!
 } else //regex failed, meaning all characters actually match

Pretty similar to ioseb's, but you need to include A-Z because uppercase is different from lowercase. He has written a great guide to the characters already so I'll just present an alternative regex.

I rely on negation instead (the ^ at the start, which when included at the start of a character class '[]', it has a different meaning instead), followed by the string of "allowed characters".

That way, if the regex finds anything that isn't an allowed character (the [] means one character), it'll stop parsing and return true, which means an invalid string was found.

answered Jun 15, 2012 at 8:23

xiankai

2,7713 gold badges28 silver badges31 bronze badges

4 Comments

Shikiryu Over a year ago

using [ and ] as delimiters is kinda awkward IMHO.

xiankai Over a year ago

What do you mean by delimiter? It's just a set of possible values for one character. In any case, what would you have instead?

Shikiryu Over a year ago

regex pattern in PHP have : 2 "delimiters" (I don't know if that's the good word to use) that surround it (usually "/", "#" or "~"). And if you didn't know that, you should know that [^xxx] means "everything but xxx". Therefore, you're twicely wrong.

xiankai Over a year ago

Thanks for the heads-up about the delimiter, but if you read clearly, the negation is the exact point of the regex. It's trying to find a non-match.

Collectives™ on Stack Overflow

php preg_match or preg_replace to validate

2 Answers 2

1 Comment

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related