Parse Linux Command with Python

Question

Here's a quick snippet of my code using pexpect:

child.expect('tc@')
child.sendline('ps -o args | grep lp_ | grep -v grep | sort -n')
child.expect('tc@')
print(child.before)
child.sendline('exit')

and then the output:

user@myhost:~/Python$ python tctest.py 
tc-hostname:~$ ps -o args | grep lp_ | grep -v grep | sort -n
/usr/local/bin/lp_server -n 5964 -d /dev/usb/lp1
/usr/local/bin/lp_server -n 5965 -d /dev/usb/lp0
{lp_supervisor} /bin/sh /usr/local/lp/lp_supervisor /dev/usb/lp0 SERIAL#1 /var/run/lp/lp_pid/usb_lp0
{lp_supervisor} /bin/sh /usr/local/lp/lp_supervisor /dev/usb/lp1 SERIAL#2 /var/run/lp/lp_pid/usb_lp1

user@myhost:~$

There's 4 lines of output. The first two lines show with printer port the usb device is assigned to (EX: first line shows port 5964 is assigned to lp1)

The 3rd and 4th lines show which device serial number is assigned to which usb port. (EX: SERIAL#1 is assigned to lp0)

I need to somehow parse that output so I can do the following:

If SERIAL#1 is not assigned to 5964:
    run some command
else:
    do something else
If SERIAL#2 is not assigned to 5965:
    run some command
else:
    do something else

I'm not sure how to manipulate that output so I can get the desired variables. Any help is appreciated.

Answer 1

You can extract port and serial information from pexpect data using re.findall and do something like this

import re
data = child.before
ports = re.findall(r'lp_server -n (\d+)', data)
# ['5964', '5965']
serials = re.findall(r'(SERIAL#\d+)', data)
# ['SERIAL#1', 'SERIAL#2']

list(zip(ports, serials))
# [('5964', 'SERIAL#1'), ('5965', 'SERIAL#2')]

for serial, port in zip(ports, serials):
    # Check if serial and port matches expectation

Answer 2

Another way of doing it is by using dictionaries to build relationships between device serial numbers and printer ports:

inString = """/usr/local/bin/lp_server -n 5964 -d /dev/usb/lp1
/usr/local/bin/lp_server -n 5965 -d /dev/usb/lp0
{lp_supervisor} /bin/sh /usr/local/lp/lp_supervisor /dev/usb/lp0 SERIAL#1 /var/run/lp/lp_pid/usb_lp0
{lp_supervisor} /bin/sh /usr/local/lp/lp_supervisor /dev/usb/lp1 SERIAL#2 /var/run/lp/lp_pid/usb_lp1"""

inString = inString.split("\n")

matches = dict()
serials = dict()

for i in range(len(inString[:2])):
    lp = inString[i][-3:]
    printerPort = int(inString[i].split("-n ")[1][:4])
    matches.update({lp:printerPort})

for i in range(2,len(inString)):
    t = inString[i].split(" ")
    lp = t[3][-3:]
    serial = t[4]
    serials.update({serial:lp})

finalLookup = dict((k,matches[v]) for k,v in serials.items())
print(finalLookup)

Output:

{'SERIAL#1': 5965, 'SERIAL#2': 5964}

Then you can do:

if not finalLookup['SERIAL#1'] == 5964:
    run some command
else:
    do something else
if not finalLookup['SERIAL#2'] == 5965:
    run some command
else:
    do something else