Question

I want to throw validation error if –

• user input contains php tags <?php (also for short tags <?)
• but I want to allow XML tags (<?xml) if there are no php tags detected.
• In the presence of both, I would like to throw error.

I have been upto the following regex now –

`(.*?)<\?(php)?[^xml](.*?)`

But it does not match if the input contains only PHP short tags.

I want to match the following –

PHP Short tag

<?

PHP tag

<?php

PHP tag in the presence of xml tag

<?php ?>
<?xml

Do not match the following

<?xml

Update

Using this regex (.*?)<\?[^x](.*?) does not detect <? charater if the input contains only <?, without any ending whitespace. I guess I just need to add a condition in the following position to check further only if more characters are there –

         |
         v
`(.*?)<\?[^x](.*?)`

If I try with this – (.*?)<\?([^x]?)(.*?), it no more excludes the xml. Do you see where I am hanging? I guess there is something which regex allows here. Any ideas?

Answer 1

Do you need regex at all? Why not just do:

if file contains '<?php'
    throw an error
if file contains '<?' but *doesn't* contain '<?xml'
    throw an error

EDIT as mentioned in comments this won’t cover a file that contains <? and <?xml (although you could count the number of occurences of <? and if this is GREATER than the number of <?xml, then throw an error).

Re regex, you have a few options. If your regex flavour supports negative lookaheads, you can look for a <? that isn’t followed by a ‘x’:

<\?(?!x)

or if it doesn’t support negative lookaheads, you could try

<\?([^x]|$)

Either of these look for the presence of a PHP flag.