字符串截取,该怎么解决

字符串截取
bri=bridge0 if1=wan if2=lan if3=vlan mac=00:11:22:1d:2d:3d ip=192.168.100.1 netmask=255.255.255.0 arp=arp state=stop

bri=bridge1 if1=wan mac=00:01:2B:4C:6D:9F ip=192.168.1.125 netmask=255.255.255.0 state=stop

这是我保存的配置文件
但是 if打头的是多选的,个数是不固定的,最多8个,我想取出 if的值
也就是
bridge0 : wan lan vlan
bridge1 : wan
这条数据我转成数组是

PHP code

Array(    [0] => Array        (            [bri] => bridge0            [if1] => wan            [if2] => lan            [if3] => vlan            [mac] => 00:11:22:1d:2d:3d            [ip] => 192.168.100.1            [netmask] => 255.255.255.0            [arp] => arp            [state] => stop        )    [1] => Array        (            [bri] => bridge1            [if1] => wan            [mac] => 00:01:2B:4C:6D:9F            [ip] => 192.168.1.125            [netmask] => 255.255.255.0            [state] => stop        ))

PHP code

$s = "bri=bridge0 if1=wan if2=lan if3=vlan mac=00:11:22:1d:2d:3d ip=192.168.100.1 netmask=255.255.255.0 arp=arp state=stop";parse_str(strtr($s, ' ', '&'), $a);print_r($a);
[解决办法]
不就是找哪个key是if开头的吗.

PHP code
[User:root Time:17:19:16 Path:/home/liangdong/php]$ php preg.php bridge0: wan lan vlanbridge1: wan[User:root Time:17:19:16 Path:/home/liangdong/php]$ cat preg.php <?php$str = <<<EOFbri=bridge0 if1=wan if2=lan if3=vlan mac=00:11:22:1d:2d:3d ip=192.168.100.1 netmask=255.255.255.0 arp=arp state=stopbri=bridge1 if1=wan mac=00:01:2B:4C:6D:9F ip=192.168.1.125 netmask=255.255.255.0 state=stopEOF;$rows = explode(PHP_EOL, $str);foreach ($rows as $row) {        $cols = preg_split('/\s+/', $row);        $line = explode('=', $cols[0])[1] . ":";        foreach ($cols as $col) {                $fields = explode('=', $col);                if (strncmp($fields[0], "if", 2) === 0) {                        $line .= " " . $fields[1];                }        }        echo $line . PHP_EOL;}?>