PHP: preg_match

Question

i need to write a case which only except the a-zA-Z0-9 characters with underscore and white space(1 or more than 1) and ignore all rest of the characters.I wrote a code but its not working properly. In those case should be wrong but its show OK

1) test msg@ 
2) test@msg  
3) test!msg

also those should be OK but currently shows wrong.

1) test msg.-(Two white space)

what i should to change in my code .pls help and see my code below.

$message=$_GET['msg'];

if(preg_match('/[^A-Za-z0-9]\W/',$message))
{
   echo "Wrong";
}
else
{
 echo "OK";
}

Community · Accepted Answer · 2023-11-17 19:22:09Z

Here's an optimized version of the one left by riad:

$message = $_GET['msg'];

if ( preg_match('/^[a-z0-9_ ]+$/i', $message) )
{
   echo 'Ok';
}
else
{
 echo 'Wrong';
}

I've removed the A-Z (uppercase) from the regular expression since the i modifier is used.

I'd also like to explain what you did wrong in the example you provided.

First, by putting the ^ inside the square brackets ([]), you're essentially doing the opposite of what you were trying to do. Place a ^ inside the square brackets means "not including."

You were missing a *, + or ? at the end of the square bracket, unless you only wanted to match a single character. The * character means 0 or more, + means 1 or more and ? means 0 or 1.

The \W means any non-word character. That's probably not what you wanted.

Finally, to starting a regular expression with ^ means that the beginning of the string you're string to match must start with whatever is after the ^. Ending the regular expression with a $ means that the string must end with the characters preceding the $.

So by typing /^[a-z0-9_ ]+$/i you're saying match a string that starts with a-z0-9_ or a space, that contains at least of those characters (+) and ends.

PHP has a lot of documentation of the PCRE regular syntax which you can find here: https://www.php.net/manual/en/reference.pcre.pattern.syntax.php.

Alex Emilov · Accepted Answer · 2012-08-10 22:16:20Z

0

$message=$_GET['msg'];

if(preg_match('/^[a-zA-Z0-9_ ]+$/i',$message))
{
  echo "Wrong";
}
else
{
  echo "OK";
}

edited Aug 10, 2012 at 22:16

user212218

answered Jun 12, 2011 at 5:41

Alex Emilov

1,2714 gold badges19 silver badges25 bronze badges

1 Comment

riad Over a year ago

It's OK. But revert. which need to show wrong that shows ok and which need to show ok it's show wrong.

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