php preg_replace frustration - php

Question

Im reluctant to ask but I cant figure out php preg_replace and ignore certain bits of the sting.
$string = '2012042410000102';
$string needs to look like _0424_102
The showing numbers are variable always changing and 2012 changes ever year
what I've tried:
^\d{4}[^\d{4}]10000[^\d{3}]$
^\d{4}[^\d]{4}10000[^\d]{3}$
Any help would be appreciated. I know it's a noob question but easy points for whoever helps.
Thanks

Answer 1

Your first regex is looking for:
The start of the string
Four digits (the year)
Any single character that is not a digit nor { or }
The number 10000
Any single character that is not a digit nor { or }
The end of the string
Your second regex is looking for:
The start of the string
Four digits (the year)
Any four characters that are not digits
The number 10000
Any three characters that are not digits
The end of the string
The regex you're looking for is:
^\d{4}(\d{4})10000(\d{3})$
And the replacement should be:
_$1_$2
This regex looks for:
The start of the string
Four digits (the year)
Capture four digits (the month and day)
The number 10000
Capture three digits (the 102 at the end in your example)
The end of the string

Answer 2

Try the following:
^\d{4}|10000(?=\d{3}$)
This will match either the first four digits in a string, or the string '10000' if there are three digits after '10000' before the end of the string.
You would use it like this:
preg_replace('/^\d{4}|10000(?=\d{3}$)/', '_', $string);
http://codepad.org/itTgEGo4

Answer 3

Just use simple string functions:
$string = '2012042410000102';
$new = '_'.str_replace('10000', '_', substr($string, 4));
http://codepad.org/elRSlCIP

Answer 4

If they're always in the same character locations, regular expressions seem unnecessary. You could use substrings to get the parts you want, like
sprintf('_%s_%s', substr($string,4,4), substr($string,13))
or
'_' . substr($string,4,4) . '_' . substr($string,13)