exec() does not work all commands i send - php

Question

I am making a website for a device so that the user can change the primary and secondary IP that it connects to. I am using 'exec()' to get the IP's for me. i made a function for that called 'File_read' that work great. the problem I am having is with saving it back to the same file. i still use 'exec()', the function is called 'file_write'. Below is my code for the two
function file_read()
{
$arr_out = "";
$arr_test_1 = "";
$arr_test_2 = "";
exec(#'cat /usr/triton/config/protman.conf | grep "Primary ="',$arr_test_1);
exec(#'cat /usr/triton/config/protman.conf | grep "Secondary ="',$arr_test_2);
$arr_out[0] = IP_edit(end($arr_test_1));
$arr_out[1] = IP_edit(end($arr_test_2));
$arr_out[2] = end($arr_test_1);
$arr_out[3] = end($arr_test_2);
return $arr_out;
}
function file_write($arr_in)
{
$save_1 = "";
$save_2 = "";
$build_1 = "";
$build_2 = "";
$build_1 = 'Primary = "'.$arr_in[0].'";';
$build_2 = 'Secondary = "'.$arr_in[1].'";';
$save_1 = #"sed -i 's/".$arr_in[2]."/".$build_1."/' /usr/triton/config/protman.conf";
$save_2 = #"sed -i 's/".$arr_in[3]."/".$build_2."/' /usr/triton/config/protman.conf";
echo "<br/>test save 1 = ".$save_1;
echo "<br/>test save 2 = ".$save_2;
exec($save_1);
exec($save_2);
}
i tested the string it builds to write to the file but and it is as follows.
sed -i 's/Primary = "10.200.26.144";/Primary = "10.98.227.30";/' /usr/triton/config/protman.conf
This is for '$save_1'. When i use it on putty it works so why does it not work with 'exec()'? am i missing something or is their a easier way to do this?

Answer 1

has PHP the rights to execute this command and access to this file ?
Also, you could try giving a second argument $out (as array) to the exec function to handle details/info