Searching and Replacing Text in a File

file_content_replacer.py

#!/usr/bin/env python

import os
import sys

nargs = len(sys.argv)

if not nargs == 5:
    print("usage: %s search_text replace_text infile outfile" % os.path.basename(sys.argv[0]))
elif sys.argv[3] == sys.argv[4]:
    print("infile and outfile must be different")
else:
    stext = sys.argv[1].replace("\\n", "\n")
    rtext = sys.argv[2].replace("\\n", "\n")
    input = sys.stdin
    output = sys.stdout
    if nargs > 3:
        input = open(sys.argv[3])
    if nargs > 4:
        output = open(sys.argv[4], 'w')
    for s in input.readlines():
        output.write(s.replace(stext, rtext))
    output.close()
    input.close()