Just can't crack regular expressions

[bluntster]

Ok, I feel like a complete dumbass because I've been trying for 3 hours to get the hang of regular expressions and I still can't get even the simplest one working. Here is the simplest validation I could think of:

-Is my input lower-case alpha chars only?
ie: "a", "aaa", "abcdefghijklmno"

-So I try this:
<?php
if(ereg("^{[a-z]*",$input))} {
echo "TRUE";
} else {
echo "FALSE";
}
?>

And yet I get TRUE regardless of what I throw at it; "a", "@#$#@", "ABC", "123"!?!

Where am I going wrong? Please help before I pull all my hair out!

[majik-sheff]

ereg('^{[a-zA-Z]+',$input)}

[majik-sheff]

The one I just gave you would match anything that started with letters... This makes sure that the whole thing is letters 🙂

ereg('^{[a-zA-Z]+$',$input)}

[[deleted]]

ereg("^{[a-z]*",$input)}

First of all, I suggest you change to preg_match. PERL Compatible regexps. Those are documented all over the place, in any PERL script/site/thingamedoodle.

Second, your regexp ,means the following:

^ = start of string
[a-z] = a through z
* = zero or more times

There isn't a string on this planet that does not start with zero or more instances of a-z. 🙂

What you want is to make sure that the entire string, from beginning to end, is made up of a-z.

So at the very least you need
^$
which means 'beginning of string''end of string'

Inbetween you want a-z:
^[a-z]$
but you want more than one occurence, in fact you want one or more (one or more, because an empty string is not made up of only a-z)
^[a-z]+$

stick that in a preg_match (the slashes define the pattern, the are not part of the pattern):

$sString = 'hello';
if (!preg_match("/^[a-z]+$/", $sString))
{
echo 'no match';
}
else
{
echo 'match';
}

---

A forum, a FAQ, what else do you need?

Time to YAPF!: http://www.hvt-automation.nl/yapf/

[bluntster]

Thanks Vincent, Majik,
You've both been very helpfull! But can I take this one step further;

$sString = 'hello';
if (!preg_match("/^{[a-zA-Z]+$/",} $sString)) {
echo 'no match';
} else {
echo 'match';
}

This is great, but ultimately what I'd like to check for is that the string contains ONLY these characters and nothing else, or better still, contains only alpha-numeric chars and spaces. Can you help me with that one too?
Thanks

[[deleted]]

"but ultimately what I'd like to check for is that the string contains ONLY these characters and nothing else,"

that is what these expressions do.
the ^ and $ make sure that you match the entire string, and the [a-z] means that the string must contain only a through z.

The key thing is the 'beginning of string' and 'end of string'

if you leave them off and just do

preg_match("/[a-z]+/", $sString)

then any string that contains one or more letters from a through z will match;
'this will match'
'34564576564657657u45634' this too, because there is a 'u' in it, which is one letter from a-z.

Oh, and to get only alphanumeric and spaces:

preg_match("/^[ a-zA-Z0-9]+$/", $sString)

[[deleted]]

Dang, did it really take me 4 minutes to type my reply? I'm getting old! :-)

PS, the Q was a regexp for 'lowercase only' 🙂

[bluntster]

Brilliant! Thanks Vincent,
That does the job just fine.

[[deleted]]

Hello regexp experts,

is there a website where I can input a string, input a result, and it would automatically create a regexp for me?

I can't freaking understand regexps at all, and I hate them anyway (too geeky for me).

For example i'm trying to change this: $var['thing'] to $var, that is remove ['thing'], spent 3 hours and gave up.

F.

[jim_keller]

to get $var['thing'] to $var, i would probably just use

$stuff = split("[", '$var[\'thing\']');
$just_var = $stuff[0];

it will split the string at [ and whatever's before [ will be the first element in array $stuff.

-Jim Keller
http://www.centerfuse.net

[jim_keller]

actually, explode would probably be better. I'm not 100% sure but I think explode() is faster than split(), and should be used if you don't need regular expression matching...
Make sure you use single quotes too, or it will try to evaluate $var, thinking that it is a variable.

$stuff = explode("[", '$var[\'thing\']');
$just_var = $stuff[0];

-Jim Keller
http://www.centerfuse.net