preg_match won't collect work correctly

Question

It seems to be working correctly, but if you put leading characters it doesn't check that and if you put ending characters it doesn't check that.

I want to make sure a string is in this format:

6 Numbers | Hyphen | 1 Number | A-Z any case | Hyphen | 5 Numbers

So like this 123456-1a-12345 and 123456-1A-12345 should work.

$string = 'this12345-1A-12345'; // This works, and it shouldn't
$string = '12345-1A-12345this'; // This also works and it shouldn't

$pattern = "([0-9]{6}[-]{1}[0-9]{1}[A-Za-z]{1}[-]{1}[0-9]{5})";
echo preg_match($pattern, $string);

What am I doing wrong? Sorry I am really new to preg_match, and I can't find any good libraries on syntax.

* See also [Open source RegexBuddy alternatives](http://stackoverflow.com/questions/89718/is-there) and [Online regex testing](http://stackoverflow.com/questions/32282/regex-testing) for some helpful tools, or [RegExp.info](http://regular-expressions.info/) for a nicer tutorial. — mario, Nov 21 '13 at 20:39

score 3 · Answer 1 · answered Nov 21 '13 at 20:37

3

You can use ^ to make the regex check for beginning of line and $ for the end of it.

$pattern = "(^[0-9]{6}[-]{1}[0-9]{1}[A-Za-z]{1}[-]{1}[0-9]{5}$)";

This pattern will only apply if the string has nothing before and after your specifications.

answered Nov 21 '13 at 20:37

kero

10,647
5
41
51

1

`()` *are* delimiters. – deceze Nov 21 '13 at 20:37
I did not know that, thought they would only be used for defining groups - thanks! – kero Nov 21 '13 at 20:39

Casimir et Hippolyte · Accepted Answer · 2013-11-21T20:48:44.553

3

You must only add anchors to mark the start and end of the pattern (and add pattern delimiters):

$pattern = "~^([0-9]{6}[-]{1}[0-9]{1}[A-Za-z]{1}[-]{1}[0-9]{5})$~";

As an aside, your pattern can be shorten to:

$pattern = '~^[0-9]{6}-[0-9][A-Z]-[0-9]{5}$~i';
preg_match($pattern, $string, $match);
print_r($match);

edited Nov 21 '13 at 20:48

answered Nov 21 '13 at 20:37

Casimir et Hippolyte

88,009
5
94
125

What does the `~` do and what does `~i` do? Can you explain that? – Arian Faurtosh Nov 21 '13 at 20:40
@deceze: Yes, I know, parenthesis can be used as delimiters but however it is the worst choice since it is very ambiguous in a regex pattern. – Casimir et Hippolyte Nov 21 '13 at 20:41
So if `~` are the new delimiters, then what is the `i` for? – Arian Faurtosh Nov 21 '13 at 20:42
@Arian: the `~` are used as pattern delimiters, the "i" is here for a case insensitive pattern. (you don't need to add lower case letters in your classes) – Casimir et Hippolyte Nov 21 '13 at 20:42
@CasimiretHippolyte Thanks for explaining it to me! I'll remember not to use `(` & `)` as delimiters! – Arian Faurtosh Nov 21 '13 at 20:45
1

@Arian: the best delimiters you can use are characters you are sure to not write in your pattern. It is not always possible, but when I see people using `/` as delimiters to treat XML like ... – Casimir et Hippolyte Nov 21 '13 at 20:47
1

@Arian: check deceze link, you will see that you can use several type of delimiters. – Casimir et Hippolyte Nov 21 '13 at 20:51
@Arian: parenthesis are special characters in a pattern, they are used to define capturing groups. – Casimir et Hippolyte Nov 21 '13 at 20:55
@CasimiretHippolyte ahhh okay, that makes sense! So don't use delimiters that can be used inside a pattern. Thanks again. – Arian Faurtosh Nov 21 '13 at 21:06
@Arian: exact <°))))))))> – Casimir et Hippolyte Nov 21 '13 at 21:10

preg_match won't collect work correctly

2 Answers2