[TUHS] ed(1) and Pipes.

Ralph Corderoy ralph at inputplus.co.uk
Sun Nov 19 02:09:09 AEST 2017

Hi Norman,

> > ed(1) pre-dates pipes.  When pipes came along, stderr was needed,
> > and lots of new idioms were found to make use of them.  Why didn't
> > ed gain a `filter' command to accompany `r !foo' and `w !bar'?
> I sometimes wonder that too.
> When I use `ed,' it is usually really qed, an extended ed written by
> the late-1970s UNIX crowd here at U of T.
> -- The ability to send part or all of a buffer to a shell command, to
> read data in from a shell command, or to send data out and replace it
> with that from the shell command:
>     >mail user ...
>     <ps -ef
>     |tr a-z A-Z

Thanks for the pointer.

I dug a little.  7th Ed. ed doesn't have the `:[rw] !foo' form.  It was
in "PDP-11 3+2", 1983-01, in filename().
Xqt is the global flag that says the `!' was present.

By the time of ex, that did have a filter, the `:w !foo' applied the
`:se nu list' settings to the output of the command, and ex also appends
a LF if the command's output doesn't end with one.  The effect, if not
the implementation, is as if the command's output was in a temporary
buffer than was `%p'-ed.  Here's ex-reimplementation nvi 1.79's attempt
at POSIX's

    :se nu list
	 1  foo	bar
	 2  xyzzy
	 3  .
    :w !head -c 10

So the line numbers are missing, but it's partly done the `se list' by
showing the tab, though `$' to mark the EOF is missing, and it has added
the LF.

Cheers, Ralph.

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