manipulate_text.py

#!/usr/bin/env python3

import sys

def read_file(fname):
    try:
        data = open(fname).read()
        return data
    except:
        return -1

def write_file(fname, d):
    try:
        open(fname, 'w').write(d)
        return 0
    except Exception as e:
        return e


if len(sys.argv) != 2:
    print('Invalid parameters passed')
    print('Usage:')
    print('\t%s <file>' % sys.argv[0])
    sys.exit(1)

fname = sys.argv[1]
data = read_file(fname)
if data == -1:
    print('Unable to read file %s' % sys.argv[1])
    sys.exit(1)
data = data.replace('word', 'inserted word')

retval = write_file(fname, data)
if retval:
    print(retval)
    sys.exit(1)