Python Script: Extract strings matching a regex from a file

A simple python script to extract strings matching a regex from a file.

import re
import sys

#initialize with some default pattern
mainpattern = re.compile('.*')


def matchLine(line):
    result=mainpattern.search(line)
    if result is not None:
        if result.group() is not None:
            print result.group()

def matchLines(inputfile):
    for line in inputfile:
        matchLine(line)

def processFile(inputfilename):
    inputfile=open(inputfilename,'r')
    matchLines(inputfile)

def main():
    processFile(sys.argv[1])

if __name__=="__main__":
    if sys.argv.__len__()<3:
        print 'usage: match [infile] [pattern]'
    else:
        mainpattern=re.compile(sys.argv[2])
        main()