sample input file 
-----------------------------------------------------------------------------
##  this is a comment.
#  drink
klim  s0000001
milk  s0000002 milk=klim
# food
bread s0003001
rice  s0003002
# tree
pine  s0008001
oak   s0008003
-----------------------------------------------------------------------------

sample intermediate file 
-----------------------------------------------------------------------------
drink klim  s0000001 p14861v2 CzG9D0lSUmTfs 
drink milk  s0000002 milk=kli AzVa1Je1k4PVw
food  bread s0003001 xsyy0f94 Szro0OkE/myWA
food  rice  s0003002 k5p69y52 GzEyZAoMXgfEM
tree  pine  s0008001 2TxR6kg0 WzBFpFT3gf04Y
tree  oak   s0008002 Ln80g7wL GzQoL3hBdS8L6
-----------------------------------------------------------------------------

sample passwd file 
-----------------------------------------------------------------------------
euclid:OzEbHyW5D/3to:1024:101:Geometry:/home/math/euclid:/bin/bash
turing:BzHM6W1Wib8jw:1025:102:Alan Turing:/home/cs/turing:/bin/bash
erdos:Nz1clPXbUqA/Q:1026:102:Paul Erdos:/home/cs/erdos:/bin/bash
polya:BzV/p.1pmVT/6:1027:101:George Polya:/home/math/polya:/bin/bash
-----------------------------------------------------------------------------

sample MAP
-----------------------------------------------------------------------------
# department home gid
math   math         101
cs     cs           102
drink  drink        201
food   food         202
tree   plant/tree   301
flower plant/flower 302
-----------------------------------------------------------------------------

the pseudo code for account
-----------------------------------------------------------------------------
label=.....

process the input, generate the intermediate file
for each entry in intermediate file
  if a new user 
     get a unique uid
     get his(her) home gid from MAP
     generate some stuff into the script for NEW-user
  if an old one
     generate some sutff ino the script for OLD-user
end for

if NEW-user existed then   run it     endif
if OLD-user existed then   run it     endif

moving files into the log directory


The input file , intermediate file, NEW-user (if has one), and OLD-user 
(if has one) are moved into the log directory. All of them must have 
the same prefix as the label created at the beginning.
So it is easy to track the modification. 
For example, the four files may be 
    20061130.0007-data
    20061130.0007-intermediate
    20061130.0007-NEW
    20061130.0007-OLD

The NEW-user is a script. When it is run, the new users will be added.
Of course, there are many things to do. For example, create the home directory,
set the quota, setup the environment and update the passwd entry.
But here you need to update the passwd entry only.

The OLD-user is a script. When is is run, the password for existed users 
will be changed. (The cipher field in passwd.)

You must invent a method to maintain the unique uid.

You must invent a method to generate a random password.

The code to generate a cipher for a given password is 
----------------------------------------------------------------------------
#include <stdio.h> 
#include <sys/types.h>
#include <time.h>
#include <crypt.h> 

main(int args, char *argv[])
{
  char salt[3];
  char passwd[16];
  int t;

  time((time_t*)&t);
  salt[0] = ((t&0x0000FFFF)    ) % 26 + 'A';
  salt[1] = ((t&0xFFFF0000)>>16) % 26 + 'a';
  salt[2] = '\0';

  if( args == 1 ){
    scanf("%s", passwd);
    printf("%s\n", crypt(passwd,salt));
  }
  else if( args == 2 )
    printf("%s\n", crypt(argv[1],salt));
  else if( args == 3 )
    printf("%s\n", crypt(argv[1],argv[2]));
}
----------------------------------------------------------------------------