Combining 2 preg matches.

[frizzle]

Hi group,

I have a function which validates a string using preg match.
A part looks like

if( !preg_match( '/^([a-z0-9]+(([a-z0-9_-]*)?[a-z0-9])?)$/', $string )
||
preg_match( '/(--|__)+/' ,$string) ) {

i wonder how i could combine those two into one ...
I tried a few different options of putting the second match into the
first one,
using things like [^__]+ etc, but nothing worked for me.
it should prevent double (or more) dashes or underscores behind each
other.
hello-there = ok
hello--there != ok

Any help would be great.

Frizzle.

[Csaba Gabor]

frizzle wrote:

I have a function which validates a string using preg match.
A part looks like

if( !preg_match( '/^([a-z0-9]+(([a-z0-9_-]*)?[a-z0-9])?)$/', $string )
||
preg_match( '/(--|__)+/' ,$string) ) {

i wonder how i could combine those two into one ...
I tried a few different options of putting the second match into the
first one,
using things like [^__]+ etc, but nothing worked for me.
it should prevent double (or more) dashes or underscores behind each
other.
hello-there = ok
hello--there != ok

Is hello-_there ok?
Is hello_-there ok?
Is _hello-there ok?

If the answer to the above three questions is no, then the following
should do the trick. Note that this implies that the final character
could be a - or _:

if (preg_match('/^([a-z0-9][-_]?)+$/', $string)) { ... }

Csaba Gabor from New York

[Chung Leong]

frizzle wrote:

Hi group,

I have a function which validates a string using preg match.
A part looks like

if( !preg_match( '/^([a-z0-9]+(([a-z0-9_-]*)?[a-z0-9])?)$/', $string )
||
preg_match( '/(--|__)+/' ,$string) ) {

i wonder how i could combine those two into one ...
I tried a few different options of putting the second match into the
first one,
using things like [^__]+ etc, but nothing worked for me.
it should prevent double (or more) dashes or underscores behind each
other.
hello-there = ok
hello--there != ok

Any help would be great.

Frizzle.

What you need is a lookahead and lookbehind assertion on the dash and
underscore, stating that they're acceptable only if there're letters in
front and behind them:

/^(?:[a-z]|(?<=[a-z])[-_](?=[a-z]))+$/

[frizzle]

Chung Leong wrote:

frizzle wrote:

Hi group,

I have a function which validates a string using preg match.
A part looks like

if( !preg_match( '/^([a-z0-9]+(([a-z0-9_-]*)?[a-z0-9])?)$/', $string )
||
preg_match( '/(--|__)+/' ,$string) ) {

i wonder how i could combine those two into one ...
I tried a few different options of putting the second match into the
first one,
using things like [^__]+ etc, but nothing worked for me.
it should prevent double (or more) dashes or underscores behind each
other.
hello-there = ok
hello--there != ok

Any help would be great.

Frizzle.

What you need is a lookahead and lookbehind assertion on the dash and
underscore, stating that they're acceptable only if there're letters in
front and behind them:

/^(?:[a-z]|(?<=[a-z])[-_](?=[a-z]))+$/

/^(?:[a-z]|(?<=[a-z])[-_](?=[a-z]))+$/

wowowow, could you explain a little on this ?
like the : and ?<= parts

(i assume 0-9 should still be included??)

Frizzle.

[frizzle]

frizzle wrote:

Chung Leong wrote:

frizzle wrote:

Hi group,
>
I have a function which validates a string using preg match.
A part looks like
>
if( !preg_match( '/^([a-z0-9]+(([a-z0-9_-]*)?[a-z0-9])?)$/', $string )
||
preg_match( '/(--|__)+/' ,$string) ) {
>
i wonder how i could combine those two into one ...
I tried a few different options of putting the second match into the
first one,
using things like [^__]+ etc, but nothing worked for me.
it should prevent double (or more) dashes or underscores behind each
other.
hello-there = ok
hello--there != ok
>
Any help would be great.
>
Frizzle.

What you need is a lookahead and lookbehind assertion on the dash and
underscore, stating that they're acceptable only if there're letters in
front and behind them:

/^(?:[a-z]|(?<=[a-z])[-_](?=[a-z]))+$/

/^(?:[a-z]|(?<=[a-z])[-_](?=[a-z]))+$/

wowowow, could you explain a little on this ?
like the : and ?<= parts

(i assume 0-9 should still be included??)

Frizzle.

Still curious after the explanation, but just letting you know it works
axactly as it should ..

Frizzle.

[Rik]

frizzle wrote:

Chung Leong wrote:

>frizzle wrote:

>>Hi group,

I have a function which validates a string using preg match.
A part looks like

if( !preg_match( '/^([a-z0-9]+(([a-z0-9_-]*)?[a-z0-9])?)$/',
$string )
>
preg_match( '/(--|__)+/' ,$string) ) {

i wonder how i could combine those two into one ...
I tried a few different options of putting the second match into the
first one,
using things like [^__]+ etc, but nothing worked for me.
it should prevent double (or more) dashes or underscores behind each
other.
hello-there = ok
hello--there != ok

Any help would be great.

Frizzle.

What you need is a lookahead and lookbehind assertion on the dash and
underscore, stating that they're acceptable only if there're letters
in front and behind them:

/^(?:[a-z]|(?<=[a-z])[-_](?=[a-z]))+$/

wowowow, could you explain a little on this ?
like the : and ?<= parts

non-capturing group (usefull when you just want to match, and don't need the
exact matched portion):
http://www.regular-expressions.info/brackets.html

positive lookbehind:
http://www.regular-expressions.info/lookaround.html

$regex ='/ #opening delimiter
^ #start of string
(?: #start of non-capturing group
[a-z] #any character between a and z
| #OR
(?<= #start of positive lookbehind (is preceeded by..)
[a-z] #any character between a and z
) #end of positive lookbehind
[-_] #character - or _ (not incorrect, but probably better
to [_\-],[_-] or [\-_]
(?= #start of positive lookahead
[a-z] #any character between a and z
) #end of positive lookahead
) #end of non-capturing group
+ #1 or more times, greedy
$ #end of string
/x';
Human translation:
The entire(1) string consists of 1 or more (2) characters [a-z] and possibly
the single characters _ or - enclosed by characters in the range [a-z].

(1) by achoring them with ^.....$
(2) by +

(i assume 0-9 should still be included??)

If you want that, yes, just change every [a-z] to [a-z0-9].

Use the /i modifier if you want a match to be case-insensitive.

Grtz,
--
Rik Wasmus

[Rik]

Rik wrote:

$regex ='/ #opening delimiter
^ #start of string
(?: #start of non-capturing group
[a-z] #any character between a and z
| #OR
(?<= #start of positive lookbehind (is preceeded
by..) [a-z] #any character between a and z
) #end of positive lookbehind
[-_] #character - or _ (not incorrect, but probably
better to [_\-],[_-] or [\-_]
(?= #start of positive lookahead
[a-z] #any character between a and z
) #end of positive lookahead
) #end of non-capturing group
+ #1 or more times, greedy
$ #end of string
/x';

It just occured to me that, allthough a wonderfull example:

$regex ='/^(?:[a-z]|[a-z][_\-][a-z])+$/';

....will do just fine.

equally so:
$regex ='/^(?:[a-z]+(?:[_\-][a-z]+))+$/';

Lookahead & -behind are unneccessary in this case, and this keep it simple.

Grtz,
--
Rik Wasmus

[frizzle]

Rik wrote:

Rik wrote:

$regex ='/ #opening delimiter
^ #start of string
(?: #start of non-capturing group
[a-z] #any character between a and z
| #OR
(?<= #start of positive lookbehind (is preceeded
by..) [a-z] #any character between a and z
) #end of positive lookbehind
[-_] #character - or _ (not incorrect, but probably
better to [_\-],[_-] or [\-_]
(?= #start of positive lookahead
[a-z] #any character between a and z
) #end of positive lookahead
) #end of non-capturing group
+ #1 or more times, greedy
$ #end of string
/x';

It just occured to me that, allthough a wonderfull example:

$regex ='/^(?:[a-z]|[a-z][_\-][a-z])+$/';

...will do just fine.

equally so:
$regex ='/^(?:[a-z]+(?:[_\-][a-z]+))+$/';

Lookahead & -behind are unneccessary in this case, and this keep it simple.

Grtz,
--
Rik Wasmus

Wow, thanks for the explanation!
Nice link there as well. Going right into my bookmarks.

Frizzle.

[Chung Leong]

Rik wrote:

It just occured to me that, allthough a wonderfull example:

$regex ='/^(?:[a-z]|[a-z][_\-][a-z])+$/';

...will do just fine.

equally so:
$regex ='/^(?:[a-z]+(?:[_\-][a-z]+))+$/';

Lookahead & -behind are unneccessary in this case, and this keep it simple.

Good point. It doesn't make sense to use assertions when you'll capture
the matches anyway.

[frizzle]

Chung Leong wrote:

Rik wrote:

It just occured to me that, allthough a wonderfull example:

$regex ='/^(?:[a-z]|[a-z][_\-][a-z])+$/';

...will do just fine.

equally so:
$regex ='/^(?:[a-z]+(?:[_\-][a-z]+))+$/';

Lookahead & -behind are unneccessary in this case, and this keep it simple.

Good point. It doesn't make sense to use assertions when you'll capture
the matches anyway.

Somehow, i believe Rik's solution, gave me problems ...

'/^(?:[a-z0-9]|[a-z0-9][_\-][a-z0-9])+$/'; gave problems.
'/^(?:[a-z0-9]|(?<=[a-z0-9])[-_](?=[a-z0-9]))+$/' didn't.

An example string that gave problems is:
really_a_made_u p_string

So i used Chung's option.

Frizzle.