t/xdd

   1 #!/usr/bin/env python
   2 """
   3 dd-alike which supports SEEK_SET seeking
   4 Copyright (C) 2011  Kirill Smelkov <kirr@navytux.spb.ru>
   5
   6 This program is free software: you can Use, Study, Modify and Redistribute it
   7 under the terms of the GNU General Public License version 2. This program is
   8 distributed WITHOUT ANY WARRANTY. See COPYING file for full License terms.
   9
  10
  11 dd's skip uses SEEK_CUR, and also it checks whether current position is >
  12 st_size after, and errors if it is, which is not good for us - in our case all
  13 files have st_size=0, like in /proc.
  14
  15 So here goes small utility
  16 $ xdd off1,size1 off2,size2 ...  <in >out
  17 """
  18 import sys
  19 from os import read, write, lseek, SEEK_SET
  20
  21
  22 # safe read
  23 def xread(fd, size):
  24         buf = ''
  25
  26         while size != 0:
  27                 chunk = read(fd, size)
  28                 if not chunk:
  29                         break
  30
  31                 buf  += chunk
  32                 size -= len(chunk)
  33
  34         return buf
  35
  36 # safe write
  37 def xwrite(fd, buf):
  38         wrote = 0
  39
  40         while buf:
  41                 size = write(fd, buf)
  42
  43                 buf    = buf[size:]
  44                 wrote += size
  45
  46         return wrote
  47
  48
  49 def main():
  50         # (offset, size)
  51         work = []
  52
  53         for arg in sys.argv[1:]:
  54                 offset, size = arg.split(',')
  55                 offset = int(offset)
  56                 size   = int(size)
  57                 work.append( (offset, size) )
  58
  59         for offset, size in work:
  60                 lseek(0, offset, SEEK_SET)
  61                 buf = xread(0, size)
  62                 xwrite(1, buf)
  63
  64
  65
  66 if __name__ == '__main__':
  67         main()