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From: mwm@eris.BERKELEY.EDU (Mike Meyer)
Newsgroups: comp.sys.amiga
Subject: Re: PIPES (was Shell scripts on AmigaDOS & Unix)
Message-ID: <2278@jade.BERKELEY.EDU>
Date: Wed, 21-Jan-87 04:35:29 EST
Article-I.D.: jade.2278
Posted: Wed Jan 21 04:35:29 1987
Date-Received: Wed, 21-Jan-87 22:51:14 EST
References: <2228@jade.BERKELEY.EDU> <1987Jan19.022653.20521@utcs.uucp> <2259@jade.BERKELEY.EDU> <2023@tekgvs.UUCP>
Sender: usenet@jade.BERKELEY.EDU
Reply-To: mwm@eris.BERKELEY.EDU (Mike Meyer)
Organization: Missionaria Phonibalonica
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I remember that posting; I also remember being singularly unimpressed
at the time. You could do similar things on CP/M-80, if you were
tricky and nasty enough.

You see, that's not pipe()s, that's just a shell script to make using
temp files look like the Unix pipe syntax. Sorta like the difference
between writing and typing; it all looks the same, but the content is
different!

For instance, I can add detab a 1Meg file and print the result using
real pipes; that execute script will run out of memory (unless there's
something really nasty I missed; always a possibility!).

The key thing about a pipe is that it's a FIFO queue, with a limited
buffer size. You can pass unlimited amounts of data through one, yet
it will always use a small amount of space. Most OS's have some kind
of facility to do this, so you can do pipes on most OS's.

What made Unix pipes so nifty was that the fifo mechanism was right
out there where the users could get to it. You didn't have to make
half-a-dozen system calls in assembler to set it up, it only took one
character on the command line.

	<mike