Python subprocess.Popen() wait for completion

Question

I am writing a small script to serially walk through a directory and run a command on the subdirectories therein.

I am running into a problem however with Popen() that it will walk through the directories and run the desired command without waiting for the previous one to finish. i.e.

for dir in dirs:
    #run command on the directory here.

it kicks off the command for each dir without caring about it afterwards. I want it to wait for the current one to finish, then kick off the next. The tool I am using on the directories is Log2timeline from SANS SIFT which takes quite a while and produces quite a bit of output. I don't care about the output, I just want the program to wait before kicking off the next.

What's the best way to accomplish this?

Thank you!

Answer 1

Use Popen.wait:

process = subprocess.Popen(["your_cmd"]...)
process.wait()

Or check_output, check_call which all wait for the return code depending on what you want to do and the version of python.

If you are using python >= 2.7 and you don't care about the output just use check_call.

You can also use call but that will not raise any error if you have a non-zero return code which may or may not be desirable

Answer 2

subprocess.check_output( ... )

will block ... and can be used instead of Popen

however if you are set on Popen

subprocess.Popen(...).communicate() 

will also block until the process returns