PHP exec 不返回 awk 输出

Question

I'm trying to get the output of the following awk command via PHP but i get no output

$time_ref = date("Y-m-d\TH:i:s",strtotime(date('c', (time() - 80)))); //2020-03-29T21:00:30

$s_string = 'awk \'$0 > "'.$time_ref.'" && $0 ~ "AAA4311A01A404C4E21ABE55"\' /var/log/syslog | tail -1';  

echo shell_exec($s_string);

Running the awk from console directly it works:

pi@raspberrypi:/var/log $ awk '$0 > "2020-03-30T10:06:28" && $0 ~ "AAA4311A01A404C4E21ABE55"' syslog

2020-03-30T10:07:40.300908+02:00 RadioBridge ESP-RSL: RESULT = {"RfRaw":{"Data":"AAA4311A01A404C4E21ABE55"}}

Any suggestion on why it does not work from PHP?

Answer 1

There are many solution. 
1) if  you run the PHP file in web, you should set the permission to the awk file. 
2) we should set the path of the "awk"
$PATH = "real path";
putenv("PATH=$PATH");
$_string = "./awk ...."

Thanks.