arrays - How to diagnose an issue with php exec function when $return is false -

hi i'm having problem script meant run multiple times successfully. using following code have diagnosed script running half time, whereas other half doesn't seem running correctly @ all.

i have figured out using $return value of exec function shown below:

exec("exec /bin/bash ./ygtoyn.sh $filename $yname 2>&1", $output, $return);  if($return !== 0){ // exec successful if $return_var set 0. !== means equal , identical, is integer , zero.    echo "file not created"; } else{    echo "file created successfully"; }  print_r($output); 

however need figure out why script not running correctly half of time. there method can use diagnose issue is? $output variable appearing empty array.

here output when run code:

file not created

array ( )

file created

array ( )

file not created

array ( )

file created

array ( )

file created

array ( )

file not created

array ( )

update 1: i've printed out value of $return 1. according link hiteksoftware means incorrect function. can explain might be?