#!/usr/bin/env python
''' Create tar archives the hard way.
The python tarfile module does that much better but it's more
an exercise and fun to see very little code is needed to manage to
create a tarball.
Support only the original tar format.
http://en.wikipedia.org/wiki/Tar_(file_format)
'''
import os, sys
from os.path import getsize, isfile, isdir, islink
from os import stat
def write_header(f, fn):
'''
100 name name of file
8 mode file mode
8 uid owner user ID
8 gid owner group ID
12 size length of file in bytes
12 mtime modify time of file
8 chksum checksum for header
1 link indicator for links
100 linkname name of linked file
'''
def rpad(s, size):
L = len(s)
return s + (size - L) * '\0'
header = rpad(fn, 100)
header += rpad('%o' % stat(fn).st_mode, 8)
header += rpad('%o' % stat(fn).st_uid, 8)
header += rpad('%o' % stat(fn).st_gid, 8)
size = getsize(fn) if isfile(fn) else 0
header += rpad('%o' % size, 12)
header += rpad('%o' % stat(fn).st_mtime, 12)
header += 8 * '\0' # 8 zeros while the cksum is computed
if islink(fn): header += 1 * '2'
elif isfile(fn): header += 1 * '0'
elif isdir(fn): header += 1 * '5'
if islink(fn): header += rpad(os.readlink(fn), 100)
else: header += 100 * '\0'
# the checksum part is shamelessy stolen from the tarfile module
# with little edit
cksum = 256 + sum(ord(h) for h in header)
header = rpad(header, 512)
header = header[:-364] + '%06o\0' % cksum + header[-357:]
f.write( header )
def write_body(f, fn):
fo = open(fn)
bytes = fo.read()
fo.close()
f.write(bytes)
zeros = 512 - len(bytes) % 512
f.write(zeros * '\0')
def write(files, out):
f = open(out, 'wb')
for fn in files:
write_header(f, fn)
if isfile(fn) and not islink(fn): write_body(f, fn)
f.close()
if __name__ == '__main__':
if len(sys.argv) < 3:
print 'Usage: batar.py <tar archive> [files | directories]'
else:
write(sys.argv[2:], sys.argv[1])
