Re: request for review: Doing direct file I/O in Emacs Lisp

[Kai Grossjohann <kai@emptydomain.de>]

Richard Stallman <rms@gnu.org> writes:

>     I understand that rationale, but in this case Eshell has a crying need
>     for being able to directly write to files.  It makes output
>     redirection thousands of times faster, and also makes it possible to
>     output to device files and named pipes.
>
> Could you tell me more?  What data does eshell want to write into
> files?  Where is the data coming from?  Is it coming from subprocesses
> started by eshell, or is it generated from eshell itself?

Both.  Like any shell, eshell provides builtins and it is able to
invoke subprocesses.  For example, you can type "find-file foo" as a
command to eshell, and eshell will then invoke the builtin find-file.

Just as a random command example, perhaps somebody would like to type
"ls > foo" at a shell prompt.  Surely that person would also use the
same command from eshell.  In eshell, ls is a builtin command, so this
is an example of redirection of output generated from eshell itself.

As another random example, perhaps people type commands similar to
"awk '{print $1}' bar > bar.out".  awk is not a builtin in eshell, so
this is an example of redirection of output generated from a
subprocess.

I would very much like to combine input and output redirection with
builtin and external commands, just as it is possible in other shells:
if I type "x | y | z > a" at a shell, then I don't normally think
about whether x, y, z are builtin commands.

Kai