Python: Import /etc/services file to a Dictionary

Question

So I have to create a python script that will import /etc/services file and write it to a dictionary.

The goal is that the port/protocol will become the key and service the value. I want to be able to print the dict entering the key info and see the service return as such:

print(yourdictionaryname["22/tcp"])
ssh

This script is the furthest I have been able to get. I found it online and it works great but it is designed to just show unused ports. Cant seem to modify it to do what i need:

# set the file name depending on the operating system
if sys.platform == 'win32':
file = r'C:\WINDOWS\system32\drivers\etc\services'
else:
file = '/etc/services'

# Create an empty dictionary
ports = dict()

# Iterate through the file, one line at a time
for line in open(file):

# Ignore lines starting with '#' and those containing only whitespace
if line[0:1] != '#' and not line.isspace():

   # Extract the second field (seperated by \s+)
   pp = line.split(None, 1)[1]

   # Extract the port number from port/protocol
   port = pp.split ('/', 1)[0]

   # Convert to int, then store as a dictionary key
   port = int(port)
   ports[port] = None

   # Give up after port 200
   if port > 200: break

# Print any port numbers not present as a dictionary key
for num in xrange(1,201):
if not num in ports:
    print "Unused port", num

sounds like there are two tasks involved in the assignment: 1) Writing the dictionary to a file. 2) Parsing that dictionary file for the port/service? Which part are you stuck on? Start by getting the dictionary (I think this script already does that) and write it out to a file. Then do step 2 — chickity china chinese chicken, Jan 26 '17 at 18:27
the answer to this question [How to write a dictionary into a file?](http://stackoverflow.com/a/20169670/1248974), shows how to save the dictionary (`ports` is the dictionary in the script you posted) to a file — chickity china chinese chicken, Jan 26 '17 at 18:36

score 3 · Answer 1 · answered Feb 16 '18 at 20:00

3

depending on what you're trying to accomplish, the socket module may be sufficient for your needs, with its getservbyname and getservbyport functions:

>>> socket.getservbyport(22)
'ssh'
>>> socket.getservbyport(22, 'udp')
'ssh'
>>> socket.getservbyport(22, 'tcp')
'ssh'
>>> socket.getservbyname('http')
80
>>> socket.getservbyname('http', 'tcp')
80
>>> socket.getservbyname('http', 'udp')
80

if you really need the dict, you could iterate over range(1, 65536) with getservbyport.

answered Feb 16 '18 at 20:00

jcomeau_ictx

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Does that actually show running services or is it just common ones – Joe Feb 16 '18 at 21:04
it reads /etc/services for you. so it contains all known services, not just the ones currently running. – jcomeau_ictx Feb 16 '18 at 21:35

score 1 · Accepted Answer · answered Jan 27 '17 at 18:05

So I had to look all around to get this to work. It is a cool function. First it detects the OS then it creates a dictionary based on the /etc/services file. Next it will parse that file for port input then return the associated service.

import sys

# set the file name depending on the operating system
if sys.platform == 'win32':
    file = r'C:\WINDOWS\system32\drivers\etc\services'
else:
    file = '/etc/services'

# Create an empty dictionary
ports = dict()

# Iterate through the file, one line at a time
for line in open(file):

    if line[0:1] != '#' and not line.isspace():
        k = line.split(None, )[1]

        # Extract the port number from port/protocol
        v = line.split('/', )[0]
        j = ''.join([i for i in v if not i.isdigit()])
        l = j.strip('\t')
        ports[k] = l

print(ports.get("22/tcp"))
print(ports.get("8080/tcp"))
print(ports.get("53/udp"))

Python: Import /etc/services file to a Dictionary

2 Answers2