#!/bin/env python

"""Change extensions of all matched files in a directory.

Usage: change_extensions ext1 ext2 [dir1 [dir2 [...]]]

    Where "ext1" is the extension files currently have, "ext2" is the
    extension they should have, and "dir<n>" is a list of directories
    in which to perform the renaming (defaulting to the current directory).

    An `extension' is the last section of a filename, starting with the
    final "." in the filename and continuing to its end - for instance,
    in "fred.jim.bob" the extension is ".bob".

    If "ext1" is the empty string (""), then files with no extension will
    be given extension "ext2" (note that this obviously won't rename files
    called something like "look.no.extension"!)

    If "ext2" is the empty string (""), then the files will end up with
    no extension.

    Note that if either of  "ext1" or "ext2" is non-empty, and does not
    start with a ".", then a "." will be prepended.
"""


import sys
import string
import os
#import posix
#import posixpath

def doit(dir,ext1,ext2):
    """Rename files in "dir" with extension "ext1" to extension "ext2"."""

    print "Directory",dir

    files = os.listdir(dir)
    files.sort()

    for file in files:
	root,ext = os.path.splitext(file)

	if ext == ext1:
	    oldfile = os.path.join(dir,file)
	    newfile = os.path.join(dir,'n-'+root+ext2)
	    print "Renaming %s to %s"%(oldfile,newfile)

	    if os.path.exists(os.path.join(dir,newfile)):
		print "*** Unable to rename %s to %s (already exists"%(oldfile,
								       newfile)
	    else:
		try:
		    os.rename(oldfile,newfile)
		except:
		    print "*** Unable to rename %s"%oldfile


def main():
    """Called from the toplevel."""

    # Extract our arguments

    arg_list = sys.argv[1:]

    # What arguments do we have?

    if len(arg_list) < 2:
	print __doc__
	return

    ext1 = arg_list[0]
    ext2 = arg_list[1]

    # Make sure the extensions start with "."
    # (unless they're the empty string)

    if len(ext1) != 0 and ext1[0] != ".":
	ext1 = "."+ext1

    if len(ext2) != 0 and ext2[0] != ".":
	ext2 = "."+ext2

    # Sort out which directories we want

    dirs = arg_list[2:]
    if len(dirs) == 0:
	dirs = ["."]

    # And process each of them

    for dir in dirs:
	# Let's be cautious...

	if os.path.isdir(dir):
	    doit(dir,ext1,ext2)
	else:
	    print "%s is not a directory"%dir


# If we're run from the shell, run ourselves

if __name__ == "__main__":
    main()


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