How did UNIX programs interact with each other, before the invention of the pipe

historical-unixpipe

I read recently, that the concept of a pipe did not come about before UNIX version 3.

But since UNIX was always about simple programs, that do one thing, composed to do more complex things: How did they manage that, without pipes in the first place?

Best Answer

IO redirection was not present in the initial PDP-7 implementation (circa 1969) but was added very shortly thereafter. With that, you can implement the moral equivalent of a pipe:

prog1 | prog2

could be implemented with

prog1 > tempfile
prog2 < tempfile
rm tempfile

In fact, pipes are often explained using this model.

The paper The Evolution of the Unix Time-sharing System by Ritchie is highly recommended for early Unix history. It states, "Pipes appeared in Unix in 1972".

Related Solutions

Bash – Races when piping two commands to a named pipe

Why not just do:

{ echo foo; echo bar;} > /tmp/p

If you want your controlling script to leave the pipe open, you can do:

exec 3<> /tmp/p

Opening a named pipe in read-write mode is to avoid that to block if the pipe hasn't been opened yet. That would instantiate it if it wasn't yet. It works on Linux at least but is not guaranteed to by POSIX.

Alternatively (and portably):

: < /tmp/p & exec 3> /tmp/p

Then instead of having each process open the named pipe, you can also do:

cmd >&3

And in the end, you'd do:

exec 3>&-

To close the writing end to let readers know it's finished.

change all <s to >s and <s to >s if you need the logic to be the other way round.

Linux – How was Unix installed in the 70’s-80’s

In the first job I had, back in 1989, we installed Unix (Interactive, owned by Kodak at the time) onto Intel 386 PCs using 3.5 inch (ca. 9 cm) floppy disks.

Best Answer

Related Solutions

Bash – Races when piping two commands to a named pipe

Linux – How was Unix installed in the 70’s-80’s

Related Question