Regular Expressions In PHP (Part 3)

siLenTz · #1 (**permalink**) 06-28-2007, 10:00 AM

You have read the first and second part already right? Now it get your
hand dirty with more regular expression in PHP lesson. In this lesson,
I will introdce you 4 more special characters that are used in regular
expressions.

The first I want to introduce is ?. ? mean optional. For example, "me?n"
which mean letter e is optional. The string that match this expression,
it should be "men" or "mn" but not "man".

() is also regular expression special character. Its job is to group characters
into a string. For simple example: "^(ab)" match only with string that is
start with letter ab. Another example: "n(am)e" will only match with
"name" but not "nae" or "ne". Another useful example, "^(ab)+" match with
string that contains one or more "ab" at the beginning. Now let use () and ?
together:

PHP Code:

      $regexp = "^[A-Za-z]+([0-9]+)?$";
    $string = "hello22";

    if (ereg($regexp, $string)) {
        print "Match...!";
    } else {
        print "Not Match...!";
    }

Let analyze what this regular expression, "^[A-Za-z]+([0-9]+)?$", does.
"^[A-Za-z]+" mean only string that start with alphabet character, and
"([0-9]+)?$" mean it is optional to have number at the end of the string.
So this expression will match with "hello", "hello2007" and "man18" but
not match with "L1fE" or "se7en".

Full-stop(.) mean any single character. For example, ".." match with
any string that contain at least 2 characters. Another example,
"^..$" match with any string that contain exactly 2 characters.
"............" there are 10 full-stops in this quote which mean only string
that contains at least 10 characters. But there are shorter way to do
it by using {}. {} mean repeating. ".{10}" is equal to ".........." and
"a{5}" is equal to "aaaaa". But {} give a powerful function that
allow us to determine the range of repeatation. For example:
"a{2,5}" mean it match to string that have at least 2 of letter a but must
be less than 6 of a letter.

I will write a very powerful email validation by using a very complex
regular expression:

PHP Code:

  <?php
    $regexp = "^[A-Za-z0-9._-]+@[A-Za-z0-9_-]+(\.[A-Za-z]+){1,2}$";
    $string = "invisal@gmail.com";

    if (ereg($regexp, $string)) {
        print "Match...!";
    } else {
        print "Not Match...!";
    }
?>

"^[A-Za-z0-9._-]+@[A-Za-z0-9_-]+(\.[A-Za-z]+){1,2}$" is match with
"invisal@gmail.com", "invisal@programmestalk.net" and "admin@admin.co.nr"
but not match with "invisal@he.co.kh.gov" because it is not possible
to have "he.co.kh.gov" domain name. Complicated? Let me explain,
"^[A-Za-z0-9._-]+@" allow only alphabet character, numbers and
".", "_" or "-" at beginning of string until it reach character @.
"[A-Za-z0-9_-]+" for domain name only allow alphabet character, numbers,
"_" and "-" until it reach it character "." in here I used "\." instead of "."
because if I use only ".", the regular expression perform "." as allow any
single character which is function of "." do in regular expression. But
I use \. mean I only need a simple fullstop character. "(\.[A-Za-z]+){1,2}$"
match any string that end with "." + alphabets and it could only be repeat
2 times. It match ".com", ".com.kh", ".us" and "co.nr" but not match with
".com.net.org" or "co.uk.com"....

That's all for the Basic Regular Expression, I hope you enjoy my tutorial
from the first part until the last part. If you don't understand any part
you can ask me questions. I glad to help

I. You can tell me, If you need
more useful regular expression, I will post it on this website

---------------- END --------------------------

From siLenTz
Regular expression journey is ending here....

Lee · #2 (**permalink**) 06-28-2007, 12:48 PM

Thanks a lot, all 3 tutorials have helped me build up a little on this function, now all i need to do is put it together which i will be doing in a script im making

siLenTz · #3 (**permalink**) 06-28-2007, 01:35 PM

Quote:

Originally Posted by Lee

Thanks a lot, all 3 tutorials have helped me build up a little
on this function, now all i need to do is put it together which i will be doing in
a script im making

Your thank give me a great motivation to write my next tutorial (which I
don't know what is going to be about)

Thanks you...

From siLenTz
Thanks....

HelloWorld · #4 (**permalink**) 06-28-2007, 02:18 PM

Thank you even though I'm not able to use your tutorial yet, since I'm now overwhelmed with various programming problems

I will surely try out your tutorial once I get done with this problem

P.S each time there's tutorial written, it just make me excited and wanting to try them out all, but I can't do multithreading (for human) lol... we don't have dual core... sigh... multithreading is a headache for me now...

Lee · #5 (**permalink**) 06-29-2007, 12:45 PM

Ok im using this in my script now that im working on, at the moment my string is:

PHP Code:

      $regexp = "^[A-Za-z0-9]";

That means that they can only use letters and numbers to start, i want to make it so thats all they can do, at the moment i could register "admin-#" i have tried:

PHP Code:

      $regexp = "^[A-Za-z0-9]$";

But then it will not let any username be correct? Am i doing something wrong or is there a different string to do this?

TeraTask · #6 (**permalink**) 06-29-2007, 01:14 PM

Lee, I don't understand your problem with the first regular expression. You want it to start with a letter. admin-# starts with "a" which is a letter.

Your second expression only allows a 1 character string (start and end are set and you've give one character in-between).

If you're trying to sanitize a username, let me recommend a different approach. I don't know the ereg syntax, so I'll give it to you with perl expressions.

PHP Code:

  <?php
$username = "admin-#";

//Strip out all non-letters and numbers from the entire string.
$username_sanitized = preg_replace('/[^a-z0-9]/i','',$username);

if ($username_sanitized == $username) {
  //No bad characters were removed, so this is a good username
  echo "<p>Good username.</p>";
} else {
  //At least one character was removed
  echo "<p>Bad username.  Try ".$username_sanitized." instead.</p>";
}
?>

siLenTz · #7 (**permalink**) 06-29-2007, 01:16 PM

PHP Code:

  $regexp = "^[A-Za-z0-9]";

This regular expression mean only alphabet or number at the beginner of
the string would match.

PHP Code:

  $regexp = "^[A-Za-z0-9]$";

This regular expression mean only one character is allow and that character
must be alphabet or number.

siLenTz · #8 (**permalink**) 06-29-2007, 01:26 PM

I think I get what you are trying to do. what you want is only alphabet or
number allowed in username. Here is the regular expression for it.

PHP Code:

  $regexp = "^[A-Za-z0-9]+$"

As I mention in the first part. "+" mean one or more. If you omit the "+", the
regular expression mean only one character allowed in string. But if you
put "+", it mean one or more alphabet or number characters allowed.

From siLenTz
Hope, it is what you want...

Lee · #9 (**permalink**) 06-29-2007, 01:41 PM

Thats exactly what i needed, its my first time using php to make a script so i guess im still learning a lot

Thanks.

siLenTz · #10 (**permalink**) 06-29-2007, 10:05 PM

Moreover, I prefer this regular expression "^[A-Za-z0-9]{4,30}$" than
"^[A-Za-z0-9]+$". "^[A-Za-z0-9]{4,30}$" mean only string, that
contain only alphabet or number, is matched, and it must be longer than
3 characters and shorter than 31 characters.

From siLenTz
Hope that is useful...

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The Following 3 Users Say Thank You to siLenTz For This Useful Post:
HelloWorld (06-28-2007), Lee (06-28-2007), TeraTask (06-29-2007)

The Following User Says Thank You to Lee For This Useful Post:
TeraTask (06-28-2007)

The Following User Says Thank You to siLenTz For This Useful Post:
TeraTask (06-28-2007)

The Following User Says Thank You to siLenTz For This Useful Post:
Lee (06-29-2007)