如何在没有拆分的情况下在PHP中保留特定字符串

I have a string like this : xxxxxxx=921919291&arg3=3729ABNTSC980z2MNM3573&arg2=2025102&arg1=7e266505e183fcb31d0ba493008fa9f881af6746.

i want to keep only the xxxxxxx=921919291 (this one is variable so i can't use an strpos)

I have tried an explode of & caractere then show only the 0 one but i have a lot of string in the same variable so it would not but good.

STR_REPLACE dosn't seems to be good because all caracteres after the = caractere are variable.

use parse_str

$str = "xxxxxxx=921919291&arg3=3729ABNTSC980z2MNM3573&arg2=2025102&arg1=7e266505e183fcb31d0ba493008fa9f881af6746";
parse_str($str);
echo $xxxxxxx;

You can also place your values into an array like so:

$str = "xxxxxxx=921919291&arg3=3729ABNTSC980z2MNM3573&arg2=2025102&arg1=7e266505e183fcb31d0ba493008fa9f881af6746";
parse_str($str, $output);
echo $output['xxxxxxx'];

More information can be found here: http://php.net/manual/en/function.parse-str.php

Try this:

echo array_shift(explode('&', $string));

You should look into phps capturing groups, an expression like this, should sort you:

^([^&]+)

This will populate capture group 1, which is accessed using the parameter of the preg_match call as an array element.