> and >> in rsh

[jeff at rlgvax.UUCP]

As a former victim of the Bourne restricted shell, I found it hard to
understand why > and >> were prohibited.  They could easily be replaced
with tee and cat (though doing this was far less efficient).  It seemed
as if the sole effect of the > restriction was to force the rsh victim
to create extra processes.

Incidentally, why have >, and < in the shell at all?  You can do it all
with "optimized" pipes.  The distinction at the shell level between
processes and data can be eliminated by having a command path which
turns out not to be executable be treated as input or output from a
file, depending on which side of the pipe it is on.  This would
simplify shell syntax.  That is,

                 uniq < data > output
could be written as
                 data | uniq | output

and
                 cat a b c | tee hold | sort -n > sorted
as
                 (a; b; c) | hold | sort -n | sorted

Some complexities do arise here.  Syntax would be needed to force an
executable to be treated as data.  The use of the path variable might
(or might not) usefully be altered.  The csh would need to have its
hashing rethought.  >> would want some other syntax (such as |>).  And
the shell would have to be a little bit smart about directly hooking
piped files to stdin where possible, rather than creating an extra
process and pipe.

               Jeffrey Kegler
               CCI Office Systems Division (formerly RLG)
               ...{allegra,seismo,mcnc,lime,we13,brl-bmd}!rlgvax!jeff