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WEBVTT captioned by howard

NOTE Introduction

00:00:00.000 --> 00:00:04.999
I have 10 minutes to talk you into

00:00:05.000 --> 00:00:07.879
giving Eshell a second chance.

00:00:07.880 --> 00:00:10.119
Have the right perspective and expectation,

00:00:10.120 --> 00:00:12.919
and I think you’ll really enjoy it.

00:00:12.920 --> 00:00:15.679
Just remember eshell is a shell,

00:00:15.680 --> 00:00:17.839
not a terminal emulator.

00:00:17.840 --> 00:00:20.279
I use both Eshell and vterm.

00:00:20.280 --> 00:00:23.479
I’m going to talk and type fast,

00:00:23.480 --> 00:00:28.999
as I have 10 reasons for you to try Eshell again.

NOTE 1. It’s an Emacs REPL

00:00:29.000 --> 00:00:32.599
1. It’s an Emacs REPL.

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I mean, check this out.

00:00:34.000 --> 00:00:36.999
Let’s start up Eshell here.

00:00:37.000 --> 00:00:41.399
Let’s just type a Lisp expression.

00:00:41.400 --> 00:00:43.919
It works.

00:00:43.920 --> 00:00:48.599
As a shell, the parens are kinda optional.

NOTE 2. It’s also a shell

00:00:48.600 --> 00:00:52.519
2. It’s also a shell.

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While eshell may look like a shell, like Bash

00:00:56.480 --> 00:00:58.559
you should view it as a REPL

00:00:58.560 --> 00:01:02.399
with parenthesis-less s-expressions.

00:01:02.400 --> 00:01:05.559
This makes sense, because a shell command with options,

00:01:05.560 --> 00:01:07.999
like this ls command,

00:01:08.000 --> 00:01:10.119
looks like an s-expression.

NOTE 3. You can mix these two modes

00:01:10.120 --> 00:01:12.879
3. You can mix these two modes.

00:01:12.880 --> 00:01:14.959
Shells can call subshells

00:01:14.960 --> 00:01:17.919
which return their output like a function call,

00:01:17.920 --> 00:01:20.799
like this Bash command.

00:01:20.800 --> 00:01:22.759
In this Eshell example,

00:01:22.760 --> 00:01:24.639
I use the output of a text file

00:01:24.640 --> 00:01:27.959
as command line arguments to ripgrep.

00:01:27.960 --> 00:01:29.639
Notice how I use braces

00:01:29.640 --> 00:01:34.759
to state that it is a call to an eshell expression.

00:01:34.760 --> 00:01:40.039
We can mix Lisp-expressions and Shell-expressions.

00:01:40.040 --> 00:01:45.599
Allow me a contrived example.

00:01:45.600 --> 00:01:50.079
Notice I use good ol' setq to create a variable.

00:01:50.080 --> 00:01:54.919
Yes, those are global Emacs variables available everywhere.

00:01:54.920 --> 00:01:59.599
In Eshell, the wildcard actually creates a list.

00:01:59.600 --> 00:02:04.479
This variable assignment doesn’t work as you might expect,

00:02:04.480 --> 00:02:07.559
as setq in Eshell is still setq,

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and it assigns variables in pairs.

00:02:10.320 --> 00:02:17.119
To make a list in Eshell, we use listify:

00:02:17.120 --> 00:02:21.239
Without parens, Eshell is in “shell mode”,

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which means that words are strings,

00:02:23.800 --> 00:02:26.879
and variables need to be prefixed with dollar signs.

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A command can have both Eshell and Lisp expressions.

00:02:32.400 --> 00:02:34.559
As you can see here,

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I have a call to ripgrep,

00:02:37.120 --> 00:02:40.319
but part of it is an s-expression.

00:02:40.320 --> 00:02:42.239
Remember the differences:

00:02:42.240 --> 00:02:46.159
With parens, eshell treats it as Lisp,

00:02:46.160 --> 00:02:49.199
like the last line in my example.

00:02:49.200 --> 00:02:53.919
With braces, eshell follows these shell-like rules:

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First, if it looks like a number, it's a number.

00:02:57.160 --> 00:02:59.439
Otherwise, eshell converts it to a string

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(quotes, like a shell, groups words).

00:03:03.680 --> 00:03:07.519
What about this mix between functions and executables

00:03:07.520 --> 00:03:10.839
for the first word?

00:03:10.840 --> 00:03:15.439
Functions that begin with eshell are called first.

00:03:15.440 --> 00:03:19.079
Next in priority are executables on your $PATH,

00:03:19.080 --> 00:03:22.159
then matching Lisp functions.

00:03:22.160 --> 00:03:23.940
You can actually switch this order

00:03:23.941 --> 00:03:27.559
with the `eshell-prefer-lisp-functions` variable.

NOTE 4. Emacs is better than shell

00:03:27.560 --> 00:03:31.759
4. Emacs is actually better than shell.

00:03:31.760 --> 00:03:35.199
If the following works, why would you call

00:03:35.200 --> 00:03:40.039
expr or bc or dc, or any of those other calculators?

00:03:40.040 --> 00:03:43.639
You can just call a Lisp expression.

00:03:43.640 --> 00:03:47.999
Why call less or more when you could call view-file?

00:03:48.000 --> 00:03:52.839
Here, I’ve aliased less to view-file.

00:03:52.840 --> 00:03:57.559
Load it up, and it shows up in an Emacs mode.

00:03:57.560 --> 00:04:01.519
Just like with less, if you hit q,

00:04:01.520 --> 00:04:05.759
you go back to your Eshell terminal.

00:04:05.760 --> 00:04:08.439
I do have an improvement, though.

00:04:08.440 --> 00:04:10.479
The problem with view-file is

00:04:10.480 --> 00:04:13.399
it takes a single file as an argument.

00:04:13.400 --> 00:04:15.719
In a shell, we might want to view more than one.

00:04:15.720 --> 00:04:18.719
So let’s make a solution to that.

00:04:18.720 --> 00:04:20.999
This function will call the first function

00:04:21.000 --> 00:04:22.159
with the first argument,

00:04:22.160 --> 00:04:26.679
and the second function with each of the rest.

00:04:26.680 --> 00:04:29.559
This allows me to make a version of less

00:04:29.560 --> 00:04:33.159
that calls view-file on the first [argument] given,

00:04:33.160 --> 00:04:36.079
but open in another window for each additional file.

NOTE 5. Better regular expressions

00:04:36.080 --> 00:04:41.239
5. Better regular expressions.

00:04:41.240 --> 00:04:44.799
Can’t remember regular expressions when calling

00:04:44.800 --> 00:04:48.639
grep or some other search function? Use the rx macro.

00:04:48.640 --> 00:04:55.919
Here I call ripgrep again, but this time,

00:04:55.920 --> 00:05:00.679
I’m using a Lisp expression calling the rx macro

00:05:00.680 --> 00:05:04.719
to look for UUIDs in the files in my current directory.

00:05:04.720 --> 00:05:08.159
But I have another improvement for this.

00:05:08.160 --> 00:05:13.479
While the rx macro is freaking cool for Emacs Lisp,

00:05:13.480 --> 00:05:15.919
it doesn’t always translate to regular expressions

00:05:15.920 --> 00:05:20.079
accepted by most commands.

00:05:20.080 --> 00:05:25.199
The (I have no idea how to pronounce this) pcre2el project

00:05:25.200 --> 00:05:28.519
can convert from a Lisp regular expression

00:05:28.520 --> 00:05:31.359
to Perl-compatible regular expressions (PCRE)

00:05:31.360 --> 00:05:33.519
acceptable by most search commands.

00:05:33.520 --> 00:05:37.879
I’ve created a new macro here, prx,

00:05:37.880 --> 00:05:41.319
that translates the output of the rx macro.

00:05:41.320 --> 00:05:46.519
This allows me to type something much more readable,

00:05:46.520 --> 00:05:48.519
and probably easier to remember.

00:05:48.520 --> 00:05:54.679
Certainly easier than this freaking regular expression.

00:05:54.680 --> 00:05:59.439
I’ve got an even better improvement.

00:05:59.440 --> 00:06:03.559
The rx macro with regular expression snippets

00:06:03.560 --> 00:06:05.759
can be assigned to key words

00:06:05.760 --> 00:06:08.679
that I can then take advantage of.

00:06:08.680 --> 00:06:13.479
Now our command would be much simpler to type.

NOTE 6. Loops are better with predicates

00:06:13.480 --> 00:06:16.159
6. Loops are better with predicates.

00:06:16.160 --> 00:06:18.759
Let’s say you want to remove the execute bit

00:06:18.760 --> 00:06:20.479
from files that have it.

00:06:20.480 --> 00:06:24.399
In a shell like bash, you need both a for loop and an if,

00:06:24.400 --> 00:06:26.599
as you can see in this example.

00:06:26.600 --> 00:06:31.559
With eshell, use a predicate to combine into a simple loop.

00:06:31.560 --> 00:06:34.359
The paren x after a file glob

00:06:34.360 --> 00:06:36.879
filters for only files marked as executable.

00:06:36.880 --> 00:06:43.559
Now here is another improvement.

00:06:43.560 --> 00:06:47.959
Since we often type loops to execute on one command,

00:06:47.960 --> 00:06:49.519
what about creating a function

00:06:49.520 --> 00:06:50.999
that can do this all in one go?

00:06:51.000 --> 00:06:57.599
This do function splits the arguments on that double colon,

00:06:57.600 --> 00:07:00.079
where the left side is a single statement to run,

00:07:00.080 --> 00:07:02.599
and the right side is a list of files.

00:07:02.600 --> 00:07:05.839
I have to append and flatten it

00:07:05.840 --> 00:07:07.639
in order for it to work.

00:07:07.640 --> 00:07:09.399
It loops through each file,

00:07:09.400 --> 00:07:12.079
creating an eshell command with the file appended.

00:07:12.080 --> 00:07:15.759
With this, I can remove the execute bit

00:07:15.760 --> 00:07:20.759
on all CSV files that have it.

00:07:20.760 --> 00:07:24.319
I see that my example wasn’t too good, as most commands

00:07:24.320 --> 00:07:29.039
like chmod accept multiple files, but you get the idea.

00:07:29.040 --> 00:07:33.159
In my final, larger form on my website,

00:07:33.160 --> 00:07:35.279
I don’t assume the command expression accepts

00:07:35.280 --> 00:07:36.719
a file as a final argument,

00:07:36.720 --> 00:07:39.639
as I can also replace underscores with the filename.

NOTE 7. Output of last command

00:07:39.640 --> 00:07:45.399
7. Output of last command.

00:07:45.400 --> 00:07:48.799
Most shells have a special variable

00:07:48.800 --> 00:07:52.839
like $? for the exit code of the last command.

00:07:52.840 --> 00:07:55.919
While reading through the source code,

00:07:55.920 --> 00:07:58.799
I noticed that the $$ refers to

00:07:58.800 --> 00:08:00.599
the output of the last command.

00:08:00.600 --> 00:08:05.799
This seems pretty cool.

00:08:05.800 --> 00:08:10.759
However, Eshell returns true or nil

00:08:10.760 --> 00:08:12.719
when running external commands,

00:08:12.720 --> 00:08:15.879
so accessing the output from a call to ls

00:08:15.880 --> 00:08:19.479
doesn’t work as expected.

00:08:19.480 --> 00:08:21.119
But this is Emacs.

00:08:21.120 --> 00:08:23.159
We can fix that.

00:08:23.160 --> 00:08:28.119
After running any command, eshell sets these four variables.

00:08:28.120 --> 00:08:33.519
I can hook a function call after every Eshell command.

00:08:33.520 --> 00:08:36.759
Using buffer-substring,

00:08:36.760 --> 00:08:39.279
I store the output into a global variable,

00:08:39.280 --> 00:08:43.599
and extend Eshell’s special variables list.

00:08:43.600 --> 00:08:46.519
In my Emacs configuration,

00:08:46.520 --> 00:08:48.479
I turned this variable into a ring,

00:08:48.480 --> 00:08:51.439
so while $$ works,

00:08:51.440 --> 00:08:54.399
so does array sub-scripting on that variable.

00:08:54.400 --> 00:08:58.399
This allows me to run a command

00:08:58.400 --> 00:09:02.279
and use the output from that command more than once.

00:09:02.280 --> 00:09:05.279
The code for this is a bit longer,

00:09:05.280 --> 00:09:08.519
so you’ll need to see my Emacs configuration for details.

NOTE 8. Redirection back to Emacs

00:09:08.520 --> 00:09:13.439
8. Redirection back to Emacs.

00:09:13.440 --> 00:09:14.879
Output of any command

00:09:14.880 --> 00:09:18.519
can go to kill-ring (or the clipboard).

00:09:18.520 --> 00:09:21.079
Think of the implications.

00:09:21.080 --> 00:09:23.839
You don’t have to go into text selection mode.

00:09:23.840 --> 00:09:26.239
Just grab the output.

00:09:26.240 --> 00:09:30.279
In fact, with our $$ improvement,

00:09:30.280 --> 00:09:33.239
we can always copy the output from the last command

00:09:33.240 --> 00:09:34.079
to the clipboard.

00:09:34.080 --> 00:09:37.999
Better yet, let’s write the output

00:09:38.000 --> 00:09:39.399
to our engineering notebook.

00:09:39.400 --> 00:09:41.679
Here’s my idea.

00:09:41.680 --> 00:09:46.079
First, create a capture template that takes a string,

00:09:46.080 --> 00:09:48.199
or if called interactively, the region,

00:09:48.200 --> 00:09:51.879
and that does an immediate-finish after inserting

00:09:51.880 --> 00:09:53.879
that string to the default notes file.

00:09:53.880 --> 00:09:57.679
Next, create a wrapper function

00:09:57.680 --> 00:10:01.559
to call org-capture-string to run that template.

00:10:01.560 --> 00:10:07.639
Finally, we add our new function to eshell-virtual-targets.

00:10:07.640 --> 00:10:08.759
Let’s see this in action.

00:10:08.760 --> 00:10:15.707
I have a CSV file of user information.

00:10:15.708 --> 00:10:19.719
I can use grep and cut to extract some of that

00:10:19.720 --> 00:10:26.879
and write it out to this month’s engineering notebook.

NOTE 9. Using Emacs buffers

00:10:26.880 --> 00:10:35.279
9. Using Emacs buffers.

00:10:35.280 --> 00:10:39.159
Why leave the results of eshell commands

00:10:39.160 --> 00:10:40.279
in the *eshell* buffer?

00:10:40.280 --> 00:10:44.119
Send the output into a buffer where you can use it.

00:10:44.120 --> 00:10:47.999
Here’s a call to ripgrep

00:10:48.000 --> 00:10:50.759
that searches for lines with email addresses

00:10:50.760 --> 00:10:53.519
using a complicated regular expression

00:10:53.520 --> 00:10:56.079
that I added to my prx macro.

00:10:56.080 --> 00:11:01.079
When I switch to this almost-grep buffer,

00:11:01.080 --> 00:11:03.319
I can turn on grep-mode.

00:11:03.320 --> 00:11:09.039
Now I can jump around as if I just called grep directly.

00:11:09.040 --> 00:11:14.759
Perhaps I’m proficient with my prx macro

00:11:14.760 --> 00:11:16.639
to filter out entries,

00:11:16.640 --> 00:11:19.279
but not good with shell commands

00:11:19.280 --> 00:11:23.999
that I can use in pipes to extract just one…

00:11:24.000 --> 00:11:26.039
the address column, for instance?

00:11:26.040 --> 00:11:28.959
Let’s just extract it,

00:11:28.960 --> 00:11:33.279
send it to a buffer called email-list,

00:11:33.280 --> 00:11:38.479
and now I can use Emacs commands that I know and love

00:11:38.480 --> 00:11:39.799
to edit the data directly.

00:11:39.800 --> 00:11:55.799
We currently have an over-sight

00:11:55.800 --> 00:11:58.839
that the Eshell’s built-in cat command

00:11:58.840 --> 00:12:02.719
doesn’t pipe buffer contents as standard in.

00:12:02.720 --> 00:12:07.919
So I created a bcat, a buffer cat, function to do this.

00:12:07.920 --> 00:12:09.879
So this command works

00:12:09.880 --> 00:12:14.599
to grab my email addresses I just extracted

00:12:14.600 --> 00:12:16.319
and send them to another program.

00:12:16.320 --> 00:12:20.959
If you’re interested, I have a more elaborate

00:12:20.960 --> 00:12:25.759
and yet simpler workflow surrounding sending data

00:12:25.760 --> 00:12:28.399
back and forth from Eshell to Emacs buffers.

NOTE 10. cd to remote systems

00:12:28.400 --> 00:12:35.679
10. Did I mention that you can cd to remote systems?

00:12:35.680 --> 00:12:39.879
This command uses SSH to jump to my host, goblin,

00:12:39.880 --> 00:12:44.039
start a root session, and jump to the etc directory.

00:12:44.040 --> 00:12:47.719
Remember that Tramp can be finicky

00:12:47.720 --> 00:12:52.839
if you start blinging your remote hosts with oh-my-zshell,

00:12:52.840 --> 00:12:57.790
and funky prompts and things like that,

00:12:57.791 --> 00:12:59.359
so your mileage may vary.

NOTE Summary

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In summary: Use eshell if you want

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a quick way to run commands and Emacs functions as a REPL,

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or to run an OS program but process the output with Emacs.

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Keep in mind that Eshell has two types of subshells,

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and you can mix and match during a command call.

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The rx macro is really cool.

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Eshell loops are better with filters and predicates …

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if you can remember them.

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Take advantage of Emacs buffers

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to really enhance your shell experience.

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You’ve now seen that just like Emacs,

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I’ve crafted Eshell to be my own shell creation,

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tailored to my workflow.

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So, steal my spells, cast your own magic,

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but feel free to share your incantations back to me.

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I’ve gone over my time allotment, so we’ll have to

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continue this discussion on the intertubes.

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Why yes, I have joined the birdless diaspora,

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so toot me over there.

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Thanks.