How to make the regula expression correct? - php

Question

I am not that familiar with regex or php, this line constantly return parsing error for detect email patterns:
with preg_match with the following inside which I changed from ereg:
if(!preg_match("/^(([A-Za-z0-9!#$%&'*+/=?^_{|}~-][A-Za-z0-9!#$%&'*+\/=?^_{|}~\.-]{0,63})|(\"[^(\|\")]{0,62}\"))$\", $local_array[$i]))
and:
if(!preg_match('/^(([A-Za-z0-9][A-Za-z0-9-]{0,61}[A-Za-z0-9])\|([A-Za-z0-9]+))$/', $domain_array[$i]) )
I tried to add / before and after it / for the following, it seems ok.
^(([A-Za-z0-9!#$%&'*+/=?^_`{|}~-][A-Za-z0-9!#$%&'*+/=?^_`{|}~\.-]{0,63})|(\"[^(\\|\")]{0,62}\"))$
The rest says:
Parse error: syntax error, unexpected '","' (T_CONSTANT_ENCAPSED_STRING), expecting ',' or ')'
How make it correct? It has parse errors when I switch from ereg to preg_match.
Thanks,
J.

Answer 1

Checking the validity of an e-mail according to the actual standard rather than just "[0-9A-z]#[0-9A-z]\\.(?i:[A-Z])" ?
Fantastic. As someone who uses a hyphen in their e-mail address, I wish there were more web-developers like you!
Here's the regex to match according to the RFC standard:
"/^([0-9A-Za-z\/\Q!#$%&'*+-=?^_`{}|~.\E]+|(?:[0-9A-Za-z\/\Q!#$%&'*+-=?^_`{}|~.\E]+\.\"(?:[0-9A-Za-z\/\Q!#$%&'*+-=?^_`{}|~. (),:;<>#[]\E]+|\\\\\\\\|\\\\\")+\"\.)+[0-9A-Za-z\/\Q!#$%&'*+-=?^_`{}|~.\E]+|\"(?:[0-9A-Za-z\/\Q!#$%&'*+-=?^_`{}|~. (),:;<>#[]\E]+|\\\\\\\\|\\\\\")+\")#(?:[0-9A-Za-z\-\.]+|\[[0-9A-Za-z\-\.]+\])$/"
Yhikes. As you can see there are multiple parts to that pattern, and if-statement logic is much, much faster, and helps reduce the eye-sore of a pattern this is.
So, if you care about that sort of thing, I would recommend writing a function to check the e-mail address like so:
1) Check that neither the local or domain part of the e-mail address have leading, trailing, or consecutive dots, and that it is in the correct format. e.g.
if (!preg_match("/^\.|\.\.|\.#|#\.|\.$/",$email) && preg_match("/^[^#]+?#[^\\.]+?\..+$/",$email)) {
This ensures there is an '#' symbol for the next part, and if it fails here, saves what would have been a lot of unnecessary computing.
2) Tokenize the e-mail address by '#:'
$part = explode("#",$email);
3) Of course, there could be more than one '#,' so if the array has more than 2 elements, loop through each and re-concatenate all but the final element, so that you get two strings: the local part (before the mandatory '#') and the domain part.
4) If the first element/local part of the address does not contain any quotation marks ($), then use this pattern:
$pattern = "/^[0-9A-Za-z\/\Q!#$%&'*+-=?^_`{}|~.\E]+$/";
5) Else if the local part begins AND ends with quotation marks, use this pattern:
$pattern = "/^\"(?:[0-9A-Za-z\/\Q!#$%&'*+-=?^_`{}|~. (),:;<>#[]\E]+|\\\\\\\\|\\\\\")+\"$/";
5) Else if the local part contains TWO quotation marks (one only would invalidate), use this pattern:
$pattern = "/^(?:[0-9A-Za-z\/\Q!#$%&'*+-=?^_`{}|~.\E]+\.\"(?:[0-9A-Za-z\/\Q!#$%&'*+-=?^_`{}|~. (),:;<>#[]\E]+|\\\\\\\\|\\\\\")+\"\.)+[0-9A-Za-z\/\Q!#$%&'*+-=?^_`{}|~.\E]+$/";
7) Else the first part is invalid.
8) If the local part was valid: If the second element/domain part is either encapsulated within square brackets ([]) or contains NO square brackets (you can just use substr and substr_count for this, since it will be much faster than regex), and it matches the pattern:
preg_match("/^\[?[0-9A-Za-z\-\.]+\]?$/",$domainPart);
Then it is valid.
Note: According to the standard, e-mail addresses can actually contain comments (why, I have no idea). The comments are not actually part of the e-mail address, and get removed when it is used. For that reason, I didn't bother matching them.