Replace matched lines with a replacement line over a file.

replace_line.py

#!/usr/bin/env python2

# read program arguments
import sys
program_arguments = sys.argv[1:]
if len(program_arguments) != 3:
    sys.stderr.write(
        "usage: replace_line.py [FILE] [MATCH] [REPLACE]\n"
    )
file_name, match_line, replace_line = program_arguments

# read lines from FILE, strip of new lines
with open(file_name, 'r') as f:
    lines = map(lambda l: l.strip(), f.readlines())

def map_line(line):
    '''
    Returns [REPLACE] if line matches [MATCH], otherwise return
    itself.
    '''
    if line == match_line:
        return replace_line
    else:
        return line

# write replaced lines to FILE
with open(file_name, 'w') as f:
    for line in map(map_line, lines):
        f.write(line + "\n")

# vim: ft=python ts=4 sts=4 sw=4 expandtab