I am validating the form input for a form field labeled 'tags', where users input tags that describe the uploaded image. After this validation, I preg_replace() any spaces with commas such that this input is csv input.

No matter the input, preg_match() returns 0. What am I doing wrong?

I want my tags to include:

• Begin with any letters (regardless of case) and/or numbers or space
• Contain any letters, numbers, spaces, commas, and hyphens
• End with any letters, numbers, spaces, or commas

Here is my regex string:

$regex = '/^[ ,][a-zA-Z0-9] (?:[ ,-] [a-zA-Z0-9])[ ,]$/';

This is my preg_match statement contained in an if statement where else exits the program (when preg_match returns 0).

preg_match($regex, $_POST['tags']) == 1;

Here are some example inputs and whether or not they should be valid.

• green-outline, triangle, 2d*% => invalid
• green-outline, triangle, 2d => valid
• green-outline triangle 2d => valid

I have tried the live regex tool at Regex101 but I can't figure out what's wrong.

CodePudding user response：

In that case I think something like this should work:

/^[\w, \-] $/g

NOTE: I removed the \d I had added previously since it's already included in \w.

https://regex101.com/r/sfulPW/2

Edit

Here's how that regular expression works:

1. ^ indicates the start of the line, that's where we should start matching.
2. [\w, \-] tells to match one or more of the following:
   • \w any word character or number (case insensitive)
   • , any comma
   • any space
   • \- any dash
3. $ indicates the end of the line, that's where we should stop matching.
4. The g flag allows us to make multiple matches.