Libris Britannia 4/science library(b).zip/science library(b)/INFO/PCCDEMO.ZIP/COMP1.EXE/BATCH.PRS

Text File | 1993-12-20 | 12KB | 199 lines

                                               üÇôéç àêïäÆ ╬╠╬╠╧╧╬╠╬╠╬╠╬╠╬╠╡

                                   │     In this edition,  we will give
                                   │  you a  comprehensive introduction
┌─┐         ┌─┐        ┌─┐         │  to  BATCH   FILES,  and   how  to
│ └──┐┌────┐│ └┐ ┌────┐│ └──┐      │  harness  their  power.  In future
│ ┌┐ │├─── ││ ┌┘ │ ┌──┘│ ┌┐ │      │  issues, we  will show  you how to
│ └┘ ││ ── ││ └─┐│ └──┐│ ││ │      │  give your batch  files more power
└────┘└────┘└───┘└────┘└─┘└─┘      │  and speed.  As  well  as bringing
    ┌───┐   ┌─┐                    │  you batch file  tricks and hints,
    │ ┌─┘┌─┐│ │┌────┐┌────┐        │  that will change  the way you use
    │ └┐ │ ││ ││ ── ││  ──┤        │  batch files.
    │ ┌┘ │ ││ ││ ───┤├──  │        │
    │ │  └─┘└─┘└────┘└────┘        │
    └─┘    σε± ∞≥-πε≥              │
                                   │     One  of   the   most  powerful
         ß√ απα∞ ΘΣφΩΦφ≥           │  features of Microsoft's MS-DOS is
                                   │  undoubtedly   its    ability   to
                                   │  perform batch  processing.   This
∞α≥≤Σ±Φφµ ßα≤Γτ σΦδΣ≥ ∞απΣ Σα≥√    │  may    seem     strange,    since
α ∞⌠≥≤ σε± αφ√ ∞≥-πε≥ ⌠≥Σ±.        │  historically batch processing was
                                   │  an unwieldy  process which became


largely  replaced  by interactive  │  For   small   tasks,   writing  a
processing once  faster computers  │  program  in  a  powerful language
were developed.    The  days when  │  like  Borland's  Turbo  Pascal or
using     a     computer    meant  │  Microsoft  C  is  overkill.   The
laboriously  writing  programs on  │  programs    can    become    more
paper, using a card punch machine  │  complicated   than    is   really
to prepare punched cards, booking  │  necessary and writing Pascal or C
a time to feed them into the card  │  programs   requires   a  suitable
reader of a computer, and collect  │  compiler.  A  good solution is to
the results  some time  later are  │  write  a  "program"  using MS-DOS
long gone.    Now  it's  mostly a  │  commands in a batch file.
case  of  typing  a  command  and  │
getting instant results.   So why  │     Most  operating  systems  have
use batch processing at all?       │  facilities for  batch processing;
                                   │  DEC's VMS has the Digital Command
   Well   there   are   obviously  │  Language and  Unix has  the Korn,
limits   to   what   single   DOS  │  Bourne and C  shells.  The beauty
commands can  do,  even including  │  of batch  programs  is  that they
the use of  pipes and filters (eg  │  are easy  to  write and  use, and
"dir |  more"  or "dir  | sort").  │  quite adequate  for  small tasks,


making use of  your PC easier and  │     Almost  any   DOS  application
more rewarding.   Why spend hours  │  that you use can be called from a
learning a  new computer language  │  batch file to make it work better
when  you  are  already competent  │  for you. Any command you can give
and comfortable with MS-DOS?       │  to DOS  using  a keyboard  can be
                                   │  placed in  a batch  file and runs
   The latest  version  of MS-DOS  │  just as if you keyed it in.
is version  6,  although  most of  │
the  new  features  of  version 6  │     Let's consider  a simple batch
don't    affect     batch    file  │  file.   It  is  called CHECK.BAT.
processing much, a CHOICE command  │  Note that all  MS-DOS batch files
has been added.  This means, that  │  have   the   extension   .BAT  to
now   you    can    create   real  │  distinguish   them   from   other
interactive  batch   files,  with  │  files.  The contents of CHECK.BAT
menus, questions, etc..            │  (viewable  by  "type  check.bat")
   You  could  use  programs like  │  are:
the antivirus checker  in a batch  │
file; for  example, to  check for  │  @echo off
viruses every  time  you  turn on  │  cls
your computer.                     │  echo This program checks multiple


disks in the A drive               │  then run.   Files  with   .COM or
:here                              │  .EXE are  always run  before .BAT
echo Insert next disk and          │  files,  thus   if   CHECK.COM  or
pause                              │  CHECK.EXE  exists  you  must type
chkdsk a: /f                       │  "check.bat"  to   run   the batch
goto here                          │  file.
                                   │
   This file could  be created by  │     The  batch   file   will  keep
typing "copy  con  check.bat" and  │  checking   disks   in   drive  A,
then the contents,  followed by a  │  pausing each time  and asking the
Control-Z on a  line by itself to  │  user to  press a  key when ready.
end the file.                      │  To  exit   the   batch  file  you
                                   │  can    use  the  Control-Break or
   To  run   the  batch file just  │  Control-C key  sequence. You will
type "check" by itself at the DOS  │  then    be    prompted "Terminate
prompt, while    in    the   same  │  batch job    Y/N?"    where   you
directory    as    the  check.bat  │  must respond   Y  if  you want to
file.   Unless   a   file  exists  │  quit, or  N  to  continue running
called       "check.com"       or  │  the batch program.
"check.exe",   the   file    will  │


   Starting a  command   with  an  │  end containing  the command "echo
@   character   stops   DOS  from  │  on".
echoing (showing)   that  command  │
when the batch  program runs. For  │     The PAUSE command when used by
instance, in  the  above example,  │  itself as in this program, simply
the user does  not see "echo off"  │  displays "Strike  a  key"  but if
on the  screen   as that  command  │  followed by text then it displays
runs.   And    they   do  not see  │  the   text   first.      See  the
"cls" etc  either since  the echo  │  CHECK2.BAT program for an example
function has  been turned  off by  │  of this.
the "echo off" command. All  they  │
see  is   what   is  specifically  │     Like     other     programming
echoed    to    the  screen.. the  │  languages,    batch  files  allow
message  "Insert  next  disk" and  │  control   structures    so   that
also  the  message    from    the  │  different  instructions   may  be
PAUSE    and    CHKDSK  commands.  │  executed depending on the outcome
Once      the      batch     file  │  of events. In the  above  example
terminates,  DOS   goes  back  to  │  the    most    primitive  command
echoing commands  by  itself; you  │  "GOTO"    was  used,  and  caused
do not need to have a line at the  │  program execution to  pass to the


specified   label,    which   was  │  echo This program checks multiple
specified by  typing  the label's  │  disks in the %1 drive
name   on   a  line   by   itself  │  :here
preceded  by a colon.              │  pause Insert next disk and
                                   │  chkdsk %1: /f
   To  determine  whether  or not  │  if errorlevel 0 goto here
to change  program execution, the  │  echo Bye!
IF statement  is used.   Here's a  │
better version  of  the CHECK.BAT  │     The   REM   statement   allows
progam, using the IF statement.    │  remarks; lines  starting with REM
                                   │  are not  executed but  just serve
CHECK2.BAT:                        │  to  remind  the   user  what  the
                                   │  program  is  for,   when  it  was
rem CHECK2.BAT program written in  │  written, or  any  other pertinent
July 1993                          │  information.
rem Usage:  check2 <Drive>         │
rem  Checks  disks  in  the drive  │     As long as  the error level is
specified                          │  zero, the  program loops  back to
@echo off                          │  "here".  Otherwise  it  continues
cls                                │  running  and  thus  comes  to the


next command, the Bye message and  │     The IF  statement can  also be
finishes.   DOS returns  an error  │  used with  the NOT  parameter, eg
level  of  0  from  the  previous  │  if not  errorlevel  3  goto start
command    (CHKDSK    here)    if  │  Which would send the program back
everything is okay and there were  │  to the  start  for any  exit code
no  errors.  An  examples  of  an  │  except for a value of 3.
error is the  case of there being  │
no disk in the drive!              │     Yet  another  use  of  the  IF
                                   │  statement is  to check  if a file
   The  %1  indicates  the  first  │  exists or not:
parameter;  ie   the  first  word  │  if not exist  %1.bak echo Warning
typed after the  word "check2" on  │  no backup!
the command  line.   In this case  │
it is the drive identifier, eg A:  │  Another useful  control structure
or B:  Up  to nine parameters can  │  is the FOR statement.
be specified by  using %1 through  │  AUTOEXEC.BAT:
to   %9.      The   %0  parameter  │  (this batch file is automatically
automatically  contains  the name  │  run  whenever   the  computer  is
of the batch file.                 │  powered on or booted)
                                   │


@echo off                          │     In    the    FOR    statement,
break off                          │  parameters are preceded by %% and
cls                                │  can be  any character  except for
echo Checking  all  EXE  files in  │  characters 0 to 9.   In this case
the root directory for viruses     │  the parameter was  called %%x and
for  %%x  in   (\*.exe)  do  call  │  was used  so  that for  each .EXE
vcheck %%x                         │  file in  the root  directory, the
                                   │  virus checking batch file was run
                                   │  by using the CALL command.
VCHECK.BAT:                        │
@echo off                          │     The reason that the errorlevel
scan /nomem /nopause %1 > nul      │  statements are  as  they  are, is
if  errorlevel   2  echo  Program  │  that the  if errorlevel statement
Error (Out of memory?)             │  also  accepts  greater  values as
if errorlevel 2 goto end           │  well as equal  values.   So if no
if  errorlevel   1   pause  VIRUS  │  provision was made  for exit code
FOUND! Reboot  from  clean system  │  2 (which occurs  when the program
disk now                           │  is out of memory or similar), the
:end                               │  "if errorlevel 1" statement would
                                   │  be executed  and  the  user would


think they had a virus.            │     Note that  the  examples given
                                   │  are  not   necessarily  the  best
   The   VCHECK.BAT   file   then  │  solutions,   they   were  written
scanned  the  file   given  as  a  │  solely   to   illustrate  various
parameter to  it  and if  a virus  │  facets of batch programming.
was  found  (indicated  by  a non  │
zero errorlevel)  then  a message  │  This concludes  the  tutorial,  I
was displayed asking  the user to  │  hope that it has been useful ñ
reboot  their   computer  from  a  │
"clean" disk.   This is important  │
in  case  the   virus  is  memory  │
resident, in  which case accurate  │
scanning may not  be possible and  │
more files  may  become infected.  │
Not all  virus  checking programs  │
will  return  error  levels  like  │
this,   these   exit   codes  are  │
specific  to  McAfee's  excellent  │
SCAN package.                      │
                                   │