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.

[Rik]

frizzle wrote:

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

...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

Ah, forgot that in [a-z0-9][_\-][a-z0-9] the character on the right is
already matched, so it won't work as a start for the second _ in _a_....

This one should still be working though:
$regex ='/^(?:[a-z0-9]+(?:[_\-][a-z0-9]+)*)$/';

Grtz,
--
Rik Wasmus

[frizzle]

Rik wrote:

frizzle wrote:

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

...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

Ah, forgot that in [a-z0-9][_\-][a-z0-9] the character on the right is
already matched, so it won't work as a start for the second _ in _a_....

This one should still be working though:
$regex ='/^(?:[a-z0-9]+(?:[_\-][a-z0-9]+)*)$/';

Grtz,
--
Rik Wasmus

ok, dankjewel / thanks a lot.

Frizzle.

[Chung Leong]

Rik wrote:

Ah, forgot that in [a-z0-9][_\-][a-z0-9] the character on the right is
already matched, so it won't work as a start for the second _ in _a_....

You know, I thought that was the problem initially, but then remembered
that the regular expression engine does backtracking in order to
maximise any match. When it encounters the underscore after assigning
the letter to the first subpattern, it's supposed to abandon the
previous match, backtrack to the letter, and go down the second branch.

[Rik]

Chung Leong wrote:

Rik wrote:

>Ah, forgot that in [a-z0-9][_\-][a-z0-9] the character on the right
is already matched, so it won't work as a start for the second _ in
_a_....

You know, I thought that was the problem initially, but then
remembered that the regular expression engine does backtracking in
order to
maximise any match. When it encounters the underscore after assigning
the letter to the first subpattern, it's supposed to abandon the
previous match, backtrack to the letter, and go down the second
branch.

Yes and no. It does exactly what you say, but it is simply not valid:

With the pattern:
'/^(?:[a-z0-9]|[a-z0-9][_\-][a-z0-9])+$/';
one states the entire string can be build by either [a-z0-9](1)OR
[a-z0-9][_\-][a-z0-9](2), think of them as blocks.

Let's examine it (not entirely how it works, but this instance close
enough):
(fixed width font is handy now:)
positions: 123456789012345 678901234567890
string: really_a_made_u p_string
match1: 111111_error, let's try the other option.
match2: 111112--_error, no other matches possible.

There is no possibility for a match with either (1) or (2) at the second _,
and no other options to match instead at the beginning of the string.

Grtz,
--
Rik Wasmus

[Chung Leong]

Rik wrote:

Yes and no. It does exactly what you say, but it is simply not valid:

With the pattern:
'/^(?:[a-z0-9]|[a-z0-9][_\-][a-z0-9])+$/';
one states the entire string can be build by either [a-z0-9](1)OR
[a-z0-9][_\-][a-z0-9](2), think of them as blocks.

Let's examine it (not entirely how it works, but this instance close
enough):
(fixed width font is handy now:)
positions: 123456789012345 678901234567890
string: really_a_made_u p_string
match1: 111111_error, let's try the other option.
match2: 111112--_error, no other matches possible.

There is no possibility for a match with either (1) or (2) at the second _,
and no other options to match instead at the beginning of the string.

Ah! I missed the single letter case.