Regular expression help

[lkeeney]

I am using this code for checking for a proper phone number.

$string_exp = "^[0-9 .-]+$";

I would also like to have the string be acceptable if they entered the characters N/A in place of a phone number. Can someone tell me how to change this expression to accept these three additional characters as an "or" statement to the phone number characters?

I don't fully understand the finer points of regular expressions, and haven't been able to figure this one out.

[NogDog]

You could do it as part of the regex, I suppose (adjusted for use with the preg_*() functions, which you should be using instead of ereg_*()?):

"#^(N/A|[0-9 .-])$#i" 

[lkeeney]

This did not work, and I don't know why.

I don't understand the difference between preg_*() and ereg_*()?) functions and when and why I should use one over the other in a php file.

If someone can direct me to a place where I can learn more about this I would appreciate it.

[NogDog]

I left out a repetition modifier:

<?php
$txt = 'N/A';
$result = preg_match('#^(N/A|[0-9 .-]+)$#i', $txt);
var_dump($result);
//int(1)
$txt = '123-456 789';
$result = preg_match('#^(N/A|[0-9 .-]+)$#i', $txt);
var_dump($result);
//int(1)
$txt = 'fubar';
$result = preg_match('#^(N/A|[0-9 .-]+)$#i', $txt);
var_dump($result);
//int(0)

For more info: http://www.php.net/pcre

[lkeeney]

I left out a repetition modifier:

<?php
$txt = 'N/A';
$result = preg_match('#^(N/A|[0-9 .-]+)$#i', $txt);
var_dump($result);
//int(1)
$txt = '123-456 789';
$result = preg_match('#^(N/A|[0-9 .-]+)$#i', $txt);
var_dump($result);
//int(1)
$txt = 'fubar';
$result = preg_match('#^(N/A|[0-9 .-]+)$#i', $txt);
var_dump($result);
//int(0)

For more info: http://www.php.net/pcre

Thank you. I will try and study this to see if I can understand it.

[NogDog]

A few things to help understand:

Parentheses enclose a sub-pattern, which is evaluated first (just like parentheses in PHP) and can have repetition modifiers append after the closing paren (not used in this case).

"|" is the "or" operator, so it matches if either side of the "|" matches.

I used "#" as the pattern delimiter, but it can be any of most special characters -- but you then have to escape that character within the pattern with a back-slash if you want that literal character to match. The "i" following the closing "#" makes the whole pattern case-Insensitive, so "N/A" or "n/a" would both match.

The "^" anchors the pattern to the start of the string, and the "$" to the end of the string.

[] is used to define a "character class": it matches on any of the characters or ranges of characters it contains. I used a "+" repetition modifier after it, meaning to match on one or more instances of those characters. ("*" would be used if you wanted to match on zero or more instances.)