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From: fisher@sc2a.unige.ch (Markus Fischer)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Redirection and piping
Message-ID: <151@sc2a.unige.ch>
Date: 13 Dec 89 12:19:48 GMT
References: <89345.110313MHS108@PSUVM.BITNET>
Organization: University of Geneva, Switzerland
Lines: 61

In article <89345.110313MHS108@PSUVM.BITNET>, MHS108@PSUVM.BITNET
(Mark Solsman) writes:
>    Can any one out there explain how to use the redirection and the pipeline
> features with ms-dos? [...]
> I have a hard disk utility that makes you enter
> the drive number from the keyboard. I would like to redirect the drive numbers
> from another file, so that I could run that unattended. Any help would be
> greatly appreciated!

Well, basically, you have the output redirect ('>' and '>>'), the input redirect
('<'), and the pipe ('|').  The redirect is used to send the output of a program
to a file ('>' rewrites and '>>' appends), or to get the input from a file.
This works only for programs that use standart i/o.  Neither direct keyboard
read, nor direct video addressing can be redirected; this applies to the pipe,
also.  The pipe is used when you want the output of a program to be send as the
input to another.  Basically, you could say that
	...> foo | bar
expands to
	...> foo > tmp_file
	...> bar < tmp_file
	...> del tmp_file
where the tmp_file is some unique non-existing filename, provided by DOS.

As for you example, let's say you want to run Norton's SD (speed disk).  This
program requires you to enter a drive letter (as in you example), the default
being the default current drive, followed by a <CR>.  So you simply create a
file containing the drive letter and a <CR>, let's call it drive.txt, and type:
	...> SD < drive.txt
or, if you prefer not to have this file always in you disk, type:
	...> echo C | SD
which will create the needed temporary file for you.
NOTE: you will need to reboot afterwards, as SD requires you to type one last
key *after* the job is done.  As the program traps the keyboard (to avoid an
unexpected end, messing up the disk), the buffer will be flushed before asking
for that last character, or it will be read directly from the keyboard, which
you can no longer do...

It is of course possible to create more complex input files, for example for
an editor... (which uses standard input ! most do not...)  I have even written
a simple program, called `write', which works a little like the `echo' command,
but with more options. For example, 
	...> write C$_Y$_exit$_
produces a file containing:
	C<CR-LF>
	Y<CR-LF>
	exit<CR-LF>

But be warned: when unsing a pipe, the program will run with the file being it's
only input!  You can no longer answer to unexpected questions, nor can you type
that last character after the "All done, strike any key to return to DOS"...
So you better try everything out when you can harmlessly reboot any time!

Hope this helps

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