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phpregexpreg-matchdelimiter

Beginner PHP help needed

I have been learning PHP for some time now and I wanted one clarification.

I have seen the preg_match function called with different delimiting symbols like:

preg_match('/.../')

and

preg_match('#...#')

Today I also saw % being used.

My question is two part:

What all characters can be used?

And is there a standard ?

Solution

  • Any

    • non-alphanumeric
    • non-whitespace and
    • non-backslash ASCII character

    can be used as delimiter.

    Also if you using the opening punctuation symbols as opening delimiter:

    ( { [ <

    then their corresponding closing punctuation symbols must be used as closing delimiter:

    ) } ] >

    The most common delimiter is /.
    But sometimes it's advised to use a different delimiter if a / is part of the regex.

    Example:

    // check if a string is number/number format:
if(preg_match(/^\d+\/\d+$/)) {
  // match
}

    Since the regex contains the delimiter, you must escape the delimiter found in the regex.

    To avoid the escaping it is better to choose a different delimiter, one which is not present in the regex, that way your regex will be shorter and cleaner:

    if(preg_match(#^\d+/\d+$#))