the script is already running.
I tried 'php distribution.php'.
the sh: line 2: error comes before the if command. The if command is good.
for some reason it echoes 2 lines, like ...  $ps = shell_exec("pgrep -fl $script_name |grep -v $my_pid ");
is twice.

sh: line 2: 27834: command not found
27834 php distribution.php
27834