preg_match: number-alphabets and commas only

You want:

/^[a-zA-Z0-9,]+$/

You need the start ^ and end $ of string anchors. Without them the regex engine will look for any of those characters in the string and if it finds one, it will call it a day and say there's a match. With the anchors, it forces the engine to look at the whole string. Basically:

• /[a-zA-Z0-9,]+/ matches if any of the characters are alphanumeric + comma.
• /^[a-zA-Z0-9,]+$/ matches if all of the characters are alphanumeric + comma.

if(preg_match('/^[0-9a-z,]+$/i', $cst_value)) {
  // valid input..contains only alphabet,number and comma.
}else{
  // invalid
}

We pass the following to preg_match : /^[0-9a-z,]+$/i

Explanation:

• / : regex delimiters.
• ^ : start anchor
• [..] : Char class
• 0-9 : any digit
• a-z : any alphabet
• , : a comma. comma is not a regex metachar, so you need not escape it
• + : quantifier for one or more. If an empty input is considered valid, change + to *
• $ : end anchor
• i : to make the matching case insensitive.