Re: Design question(s), re: why use of tmp-files or named-pipes(/dev/fd/N) instead of plain pipes?

[Chet Ramey]

On 10/19/15 1:36 PM, Ken Irving wrote:

> The manpage section on process substitution could perhaps present the
> concept more clearly by starting with something like the sentence just
> above, e.g., very roughly:
> 
>     Process Substitution, taking the form of <(list) or >(list),
>     expands the process list to a filename, allowing the construct to
>     be used in place of a filename for output or input to a command.
>     It is supported on systems that support named pipes (FIFOs) or the
>     /dev/fd method of naming open files. ...
> 
> The section goes right into what seems like implementation details, and
> the use of it is only mentioned in the fourth sentence or so.

Good suggestion.  How about something like this:

Process substitution allows a process's input or output to be  referred
to  using  a  filename.   It takes the form of <(list) or >(list).  The
process list is run asynchronously, and its input or output appears  as
a filename.  This filename is passed as an argument to the current com-
mand as the result of the expansion.  If  the  >(list)  form  is  used,
writing  to  the file will provide input for list.  If the <(list) form
is used, the file passed as an argument should be read  to  obtain  the
output of list.  Process substitution is supported on systems that sup-
port named pipes (FIFOs) or the /dev/fd method of naming open files.


Chet

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/