Regular expression search and replace as an OS X service

regex-service.py

#!/usr/bin/env python

import re
import sys
import subprocess

def osascript(script):
    p = subprocess.Popen("osascript", stdout=subprocess.PIPE, stdin=subprocess.PIPE)
    stdout = p.communicate(script)[0]
    if p.returncode != 0:
        return None
    return stdout

def quote(text):
    return text.replace('"', r'\"')

def dialog(title, question):
    return osascript("""
        tell application "Finder"
            activate
            set Input to display dialog "{question}" with title "{title}" default answer "" buttons {{"Cancel", "OK"}} default button 2
            return text returned of Input as string
        end tell""".format(title=quote(title), question=quote(question)))

def main():
    input = sys.stdin.read()

    regex = dialog("RegEx", "Regular Expression e.g. /foo/bar/g")
    if not regex:
        sys.stdout.write(input)
        sys.exit(0)
    
    sep = regex[0]
    try:
        _, find_re, rep, opt = regex.split(sep)
    except ValueError:
        sys.stdout.write(input)
        sys.exit(0)
    
    flags = 0
    count = 1
    if "i" in opt:
        flags |= re.I
    elif "g" in opt:
        count = 0
    
    sys.stdout.write(re.sub(find_re, rep, input))

if __name__ == "__main__":
    main()