Store value of os.system or os.popen

Question

I want to grep the error's out of a log file and save the value as an error. When I use:

errors = os.system("cat log.txt | grep 'ERROR' | wc -l")

I get the return code that the command worked or not. When I use:

errors = os.popen("cat log.txt | grep 'ERROR' | wc -l")

I get what the command is trying to do.

When I run this in the command line I get 3 as thats how many errors there are.

Can anyone suggest another way in Python that will allow me to save the value of this bash command?

Thanks

Answer 1

popen is deprecated. Use subprocess instead. For example, in your case:

p1 = Popen(["cat", "log.txt"], stdout=PIPE)
p2 = Popen(["grep", "ERROR"], stdin=p1.stdout, stdout=PIPE)
output = p2.communicate()[0]