Exec（）命令和脚本流程

Question

I'm just not sure... Does a script with exec(....) wait until the exec() is complete before continuing?

for instance my script will flow like this....

1. Copy PDF file from AWS to web server
2. Convert PDF file to JPG (exec())
3. Upload JPG to AWS
4. Delete both files from server.

Repeat 10,000 times...

Do i need to write something to halt the code until the exec is complete? or can use the exec command, move the files, then delete the files? My concern is the program will try to delete the files before they are converted.

I hope this is clear and thanks...

Answer 1

AFAIK exec() (if you are talking about system call) is a blocking call, hence further execution of script (whatever language it is !) will be blocked. You can use & and redirect Stderr/Stdout to /dev/null, for running process in background and wait for to complete.

Best way would be do it asynchronously :

fork() --- Child Process
if fork returns 0 
 exec() --- Command you want to process your jpegs with
in parent wait() for exec to complete