PHP preg_match for getting a string out with variable length

Question

I have the following string example: 034a412f500535454e5 Here I would get the 500 out. The search-string has always 8 digits in front and 8 digits behind. The "500" can have a different lenght of digits (p.ex. 12345).

With a lot of trial end error I found that

preg_match('/(.{8})(.*)(.{13})/', $a, $matches);

It works. But I tink that not the way it is.

I do not understand why the left side has {8} and the right is {13}.

I get my String at following:

$lastInsertedId = 500;
$numArray = str_split(bin2hex(random_bytes(8)), 8);
$newArray = [$numArray[0],$lastInsertedId,$numArray[1]]; 
$a = vsprintf('%s%s%s',$newArray);

by using:

preg_match('/^.{8}\K.*(?=.{8}$)/', $a, $matches);

the result is 50053545. It will not gives the right value back.

by using:

preg_match('/^.{8}\K.*(?=.{8}$)/', '034a412f500535454e5', $matches);

it gives 500 back

Whats wrong?

gettype($a) gives string back. I'am on php 8.1.13

Wiktor Stribiżew · Accepted Answer · 2023-01-12 11:27:10Z

2

If you want to do that with a regex, you can use

^.{8}\K.*(?=.{8}$)

See the regex demo. Use the s flag if the string contains line breaks.

Details

^ - start of string
.{8} - eight chars
\K - omit what was matched so far
.* - any zero or more chars
(?=.{8}$) - a positive lookahead that requires any eight chars followed by the end of string location to appear immediately to the right of the current location.

Also, consider using substr:

$text = '034a412f500535454e5';
echo substr($text, 8, strlen($text)-16); // => 500

answered Jan 12, 2023 at 11:27

Wiktor Stribiżew

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5 Comments

hamburger Over a year ago

Thx Wiktor. I edited my question. Wit both of your proposals I have the same problem.

hamburger Over a year ago

With preg_match('/^.{8}\K.*(?=.{13}$)/', $a, $matches); this works, again with the 13

Wiktor Stribiżew Over a year ago

@hamburger That is not related to regex. Anyway, I get "Fatal error: Uncaught Error: Undefined constant "RT" in /tmp/preview:6" error when trying your code.

hamburger Over a year ago

RT is deleted, it is only a linefeed

Wiktor Stribiżew Over a year ago

@hamburger I get 500, see this PHP demo.

hamburger · Accepted Answer · 2023-01-12 12:41:15Z

0

vsprintf gives a wrong number of digits back. strlen('034a412f500535454e5') gives 19 strlen($a) gives 25. I'am using sprintf instead.

answered Jan 12, 2023 at 12:41

hamburger

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