#!/usr/bin/python3

# written by andrewt@unsw.edu.au for COMP(2041|9044)
#
# Change the names of the specified files
# by substituting occurrances of regex with replacement
# (simple version of the perl utility rename)

import os
import re
import sys

if len(sys.argv) < 3:
    print(f"Usage: {sys.argv[0]} <regex> <replacement> [files]", file=sys.stderr)
    sys.exit(1)

regex = sys.argv[1]
replacement = sys.argv[2]

for old_pathname in sys.argv[3:]:
    new_pathname = re.sub(regex, replacement, old_pathname, count=1)
    if new_pathname == old_pathname:
        continue
    if os.path.exists(new_pathname):
        print(f"{sys.argv[0]}: '{new_pathname}' exists", file=sys.stderr)
        continue
    try:
        os.rename(old_pathname, new_pathname)
    except OSError as e:
        print(f"{sys.argv[0]}: '{new_pathname}' {e}", file=sys.stderr)