How can I check a string's pattern with given conditions (php/regex)

Question

This is what I'm trying to do,

   $line = "dsfsdf";
   if (!preg_match('/^(?=.{1,30}$)[a-zA-Z0-9\-\_]*$^/', $line))
   {
      echo 'No Match found';
   }
   else
   {
       echo 'Match found';
   }

The requirement is below,

it can have characters
it can have numbers
As special character, it can have only hyphen (-) and underscore (_) characters in it

I'm not so good at regex part. Can someone guide me how to achieve it with a simple explanation?

You must really remove ^ (start of string anchor) at the end. Try '/^[a-zA-Z0-9_-]{1,30}$/'. Or even '/^[\w-]{1,30}$/' — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Aug 10, 2017 at 11:41
Thanks a lot.. it works like a charm. so, '\w-' includes all the alphanumeric character along with '-' and '_' ? — Debraj Das
– Debraj Das, Commented Aug 10, 2017 at 11:47
Yes, \w matches what [a-zA-Z0-9_] does if no u modifier is added. Please consider accepting my answer if it works for you. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Aug 10, 2017 at 12:36
one more thing, if there's one more condition that there should be white spaces then should i use '\s' ? — Debraj Das
– Debraj Das, Commented Aug 11, 2017 at 5:24
Yes, \s stands for whitespace. [\w\s-] will be the character class. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Aug 11, 2017 at 6:42

Wiktor Stribiżew · Accepted Answer · 2017-08-10 11:49:05Z

2

You must remove ^ (start of string anchor) at the end. Also, you may replace [a-zA-Z0-9_] with \w, as without any modifiers, they are equal.

The (?=.{1,30}$) lookahead makes the regex engine only match strings with 1 to 30 characters. You may remove the lookahead and just apply the limiting quantifier to your character class.

You may use

'/^[\w-]{1,30}$/'

If you prefer a more verbose way use

'/^[a-zA-Z0-9_-]{1,30}$/'

See the PHP demo.

Both mean:

^ - start of string
[\w-]{1,30} - 1 to 30 letters/digits/underscores/- symbols
$ - end of string. NOTE that to match at the very end of the string, you need to use a D modifier, or replace $ with \z anchor (i.e. use '/^[\w-]{1,30}$/D' or '/^[\w-]{1,30}\z/' then).

answered Aug 10, 2017 at 11:49

Wiktor Stribiżew

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2 Comments

Debraj Das Over a year ago

Thanks a lot for clarifying that in a very simple way

Wiktor Stribiżew Over a year ago

@DebrajDas If you can have a \n at the end of the input and if you do not want to allow matching this string, use D modifier.

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