Difficulties in pipes between Python subprocesses in Linux

user_14861664 0
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The following script (which should take the output from p1 and pipe it to p2, and then output the result in the terminal) doesn't seem to work as expected.

Code as follows :

#!/binr/bin/python
# Script to lauch mosquitto_sub to monitor a mqtt topic -- SYNTAX : mosk topic
import sys
import subprocess

total = len(sys.argv)
cmdargs = str(sys.argv)
print ("The total numbers of args passed to the script: %d " % total)
print ("Args list: %s " % cmdargs)
# Pharsing args one by one 
print ("Script name: %s" % str(sys.argv[0]))
print ("First argument: %s" % str(sys.argv[1]))


path = str(sys.argv[1])
print (path)


p1 = subprocess.Popen(['mosquitto_sub','-h','192.168.1.100','-t',path,'-v'], shell=False, stdout=subprocess.PIPE)
p2 = subprocess.Popen(['ts'], stdin=p1.stdout, shell=False, stdout=subprocess.PIPE)

for line in p2.stdout:
    sys.stdout.write(line)

with an input as follows "./mosk2.py test/+" and whilst publishing MQTT via mosquitto on the relevant topics, I never get the expected output in the terminal

popen subprocess pipe python
1 Answers

Solved - I ended up stepping neatly around the problem (cheating) as follows :

cmd = "mosquitto_sub -h 192.168.1.100 -v -t " + topic + " | ts"
print "The command which was executed is : " , cmd

def run_command(command):
    process = subprocess.Popen(command, stdout=subprocess.PIPE, shell=True)
    while True:
        output = process.stdout.readline()
        if output == '' and process.poll() is not None:
            break
        if output:
            print output.strip()
    rc = process.poll()
    return rc

run_command(cmd) #This is the lauch of the actual command
user_148616640
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