Re: How to get eshell to do what I used to do with shell

[Joel Reicher <joel.reicher@gmail.com>]

"KARR, DAVID" <dk068x@att.com> writes:

> Section 1.1 mentions an obscure way of filtering ls output, 
> using an example like “ls -lt **/*.doc(Lk+100aM+6)”. I couldn’t 
> get any variation of that to work. It’s not clear whether it’s 
> saying that is eshell functionality, or something about the 
> most common implementations of “ls”.

Why do you think ls is doing anything interesting there?

> When I do something simple like this: “ls -l | grep "txt" | 
> sort”, all the output lines are prefixed with “(standard 
> input):”.  I haven’t searched through the info manual yet, but I 
> asked github copilot about this, and it said that “eshell/grep” 
> instead of “grep” would fix that, but that didn’t work either (I 
> don’t expect everything from copilot to be 100% accurate).

Keep in mind that when you execute a command line in eshell, 
you're executing some lisp, because eshell is written in lisp.

Depending on your configuration, the behaviour might be to execute 
a lisp function (if there is one), and that's probably the case 
with grep. If eshell fails to find a lisp function matching the 
command's name, it will then attempt to find an external program 
by that name.

Also - and this is very important - that pipe is implemented in 
lisp.

Both of these things can be overridden on demand by using the '*' 
character. For example you can force grep to call the external 
program by running

*grep

instead.

Compare the output of

grep blah foo

and

*grep blah foo

(the difference is much clearer if you do not use pipe to begin 
with)

For pipes, you can do

grep blah foo *| grep something

and this will force the use of an external shell implementation of 
pipe which, as far as I know, implicitly forces an external 
program to be used for both commands too. There may be situations 
you want the in-lisp pipe (such as piping to a lisp function 
instead of an external program).

You may also find this useful.

https://www.masteringemacs.org/article/complete-guide-mastering-eshell

Cheers,

        - Joel