Mini Shell

#! /usr/bin/python2.7

# Update a bunch of files according to a script.
# The input file contains lines of the form <filename>:<lineno>:<text>,
# meaning that the given line of the given file is to be replaced
# by the given text.  This is useful for performing global substitutions
# on grep output:

import os
import sys
import re

pat = '^([^: \t\n]+):([1-9][0-9]*):'
prog = re.compile(pat)

class FileObj:
    def __init__(self, filename):
        self.filename = filename
        self.changed = 0
        try:
            self.lines = open(filename, 'r').readlines()
        except IOError, msg:
            print '*** Can\'t open "%s":' % filename, msg
            self.lines = None
            return
        print 'diffing', self.filename

    def finish(self):
        if not self.changed:
            print 'no changes to', self.filename
            return
        try:
            os.rename(self.filename, self.filename + '~')
            fp = open(self.filename, 'w')
        except (os.error, IOError), msg:
            print '*** Can\'t rewrite "%s":' % self.filename, msg
            return
        print 'writing', self.filename
        for line in self.lines:
            fp.write(line)
        fp.close()
        self.changed = 0

    def process(self, lineno, rest):
        if self.lines is None:
            print '(not processed): %s:%s:%s' % (
                      self.filename, lineno, rest),
            return
        i = eval(lineno) - 1
        if not 0 <= i < len(self.lines):
            print '*** Line number out of range: %s:%s:%s' % (
                      self.filename, lineno, rest),
            return
        if self.lines[i] == rest:
            print '(no change): %s:%s:%s' % (
                      self.filename, lineno, rest),
            return
        if not self.changed:
            self.changed = 1
        print '%sc%s' % (lineno, lineno)
        print '<', self.lines[i],
        print '---'
        self.lines[i] = rest
        print '>', self.lines[i],

def main():
    if sys.argv[1:]:
        try:
            fp = open(sys.argv[1], 'r')
        except IOError, msg:
            print 'Can\'t open "%s":' % sys.argv[1], msg
            sys.exit(1)
    else:
        fp = sys.stdin
    curfile = None
    while 1:
        line = fp.readline()
        if not line:
            if curfile: curfile.finish()
            break
        n = prog.match(line)
        if n < 0:
            print 'Funny line:', line,
            continue
        filename, lineno = prog.group(1, 2)
        if not curfile or filename <> curfile.filename:
            if curfile: curfile.finish()
            curfile = FileObj(filename)
        curfile.process(lineno, line[n:])

if __name__ == "__main__":
    main()