While I like [[https://github.com/akermu/emacs-libvterm][vterm]], especially for logging into [[file:ha-remoting.org][remote systems]], I find Emacs’ shell, =eshell=, an interesting alternative.
If you find the documentation lacking, I [[http://www.howardism.org/Technical/Emacs/eshell-fun.html][documented most features]], and you might find the following helpful.
** Navigation and Keys
Along with the regular Emacs keybindings, Eshell comes with some interesting features:
- ~M-RET~ can be used to accumulate further commands while a command is currently running. Since all input is passed to the subprocess being executed, there is no automatic input queueing as there is with other shells.
- ~C-c C-t~ can be used to truncate the buffer if it grows too large.
- ~C-c C-r~ will move point to the beginning of the output of the last command. With a prefix argument, it will narrow to view only that output.
- ~C-c C-o~ will delete the output from the last command.
- ~C-c C-f~ will move forward a complete shell argument.
- ~C-c C-b~ will move backward a complete shell argument.
** Control-D Double Duty
Used to ~C-d~ exiting from a shell? Want it to keep working, but still allow deleting a character? We can have it both (thanks to [[https://github.com/wasamasa/dotemacs/blob/master/init.org#eshell][wasamasa]]):
#+begin_src emacs-lisp
(defun ha-eshell-quit-or-delete-char (arg)
"The `C-d' sequence closes window or deletes a character."
If any program wants to pause the output through the =$PAGER= variable, well, we don't really need that:
#+begin_src emacs-lisp
(setenv "PAGER" "cat")
#+end_src
* Aliases
Gotta have some [[http://www.emacswiki.org/emacs/EshellAlias][shell aliases]], right? We have three ways of doing that. First, enter them into an =eshell= session:
#+begin_src sh
alias less 'view-file $1'
#+end_src
Note that you need single quotes, and multiple arguments don’t really work with aliases.
Second, you can create/populate the alias file, =~/.emacs.d/eshell/alias= … as long as you don’t use those single quotes:
#+begin_src shell :tangle ~/.emacs.d/eshell/alias
alias ll ls -l $*
alias clear recenter 0
alias d dired $1
alias e find-file $1
alias less view-file $1
alias more view-file $1
alias find echo 'Please use fd instead.'
#+end_src
Which happens when you type those commands into an =eshell=.
Third, you want /control/, write a function to define the aliases:
#+begin_src emacs-lisp :tangle no
(defun ha-eshell-add-aliases ()
"Call `eshell/alias' to define my aliases."
(eshell/alias "e" "find-file $1")
(eshell/alias "d" "dired $1")
(eshell/alias "gd" "magit-diff-unstaged")
(eshell/alias "gds" "magit-diff-staged")
;; The 'ls' executable requires the Gnu version on the Mac
(eshell/alias "ll" (concat ls " -AlohG --color=always"))))
#+end_src
* Predicate Filters and Modifiers
The =T= predicate filter allows me to limit file results that have have internal =org-mode= tags. For instance, files that have a =#+TAGS:= header with a =mac= label will be given to the =grep= function:
#+begin_src sh
$ grep brew *.org(T'mac')
#+end_src
As described in [[http://www.howardism.org/Technical/Emacs/eshell-fun.html][this essay]], to extend Eshell, we need a two-part function:
1. Parse the Eshell buffer to look for the parameter (and move the point past the parameter).
2. A predicate function that takes a file as a parameter.
For the first step, we have our function /called/ as it helps parse the text at this time. Based on what it sees, it returns the predicate function used to filter the files:
#+begin_src emacs-lisp
(defun eshell-org-file-tags ()
"Helps the eshell parse the text the point is currently on,
looking for parameters surrounded in single quotes. Returns a
function that takes a FILE and returns nil if the file given to
it doesn't contain the org-mode #+TAGS: entry specified."
;; Step 1. Parse the eshell buffer for our tag between quotes
;; Make sure to move point to the end of the match:
*Note:* We can’t add it to the list until after we start our first eshell session, so we just add it to the =eshell-pred-load-hook= which is sufficient.
* Eshell Functions
Any function that begins with =eshell/= can be called with the remaining letters. I used to have a function =eshell/f= as a replacement for =find=, but the [[https://github.com/sharkdp/fd][fd]] project is better. I used to have a number =g=-prefixed aliases to call git-related commands, but now, I just need to call [[file:ha-config.org::*Magit][Magit]] instead.
However, since =eshell= is an /Emacs/ shell, I want to think of how to use Emacs buffers in a shell-focused workflow. For instance, use =view-file= instead of =less=, as it will show a file with syntax coloring, and typing ~q~ returns to your shell session.
While I like eshell’s =for= loop well enough (if I can remember the syntax), as in:
#+begin_src sh :tangle no
for file in *.org {
chmod a+x $file
}
#+end_src
I like the idea of using a /map/ structure, as in:
#+begin_src sh :tangle no
map chmod a+x *.org
#+end_src
How would this work without special syntax? Well, eshell sends the =*.org= as a list of files, which we could use as the delimiter. The downside is that we want to list the files, we need to actually /list/ the files, as in:
#+begin_src sh :tangle no
map chmod a+x (list "a.org" "c.org")
#+end_src
Pretty ugly, but that isn’t my use-case. I could introduce syntax like:
#+begin_src sh :tangle no
map chmod a+x :: *.org b.txt
#+end_src
But what if the file isn’t the last element? Well, I could replace a /keyword/, =_=, with the filename when encountered.
Here is my initial function. After separating the arguments into two groups (split on the =::= string), we iterate over the file elements, creating a /form/ that includes the filename.
#+begin_src emacs-lisp
(defun eshell/map (&rest args)
"Execute a command sequence over a collection of file elements.
The sequence and the elements are separated with a `::' string.
For instance:
map chmod a+x _ :: *.org b.txt
The `_' sequence is substituted with a single filename element,
and if not specified, the filename is appended to the command.
"
(seq-let (forms elements) (--split-when (equal it "::") args)
(dolist (element (-flatten (-concat elements)))
(let* ((form (if (-contains? forms "_")
(-replace "_" element forms)
(-snoc forms element)))
(cmd (car form))
(args (cdr form)))
(eshell-named-command cmd args)))))
#+end_src
The [[help:eshell-named-command][eshell-named-command]] takes the command separately from the arguments, so we use =car= and =cdr= on the form.
My =gst= command is just an alias to =magit-status=, but using the =alias= doesn't pull in the current working directory, so I make it a function, instead:
#+begin_src emacs-lisp
(defun eshell/gst (&rest args)
(magit-status (pop args) nil)
(eshell/echo)) ;; The echo command suppresses output
#+end_src
** Editing Files
Which an alias to [[help:find-file][find-file]] (which takes one argument), we could define a special function that can take multiple arguments, and open them in different windows. We first define a /helper function/ for dealing with multiple arguments. It takes two functions, the first function is called on the first argument, and the second function is called on each of the rest.
#+begin_src emacs-lisp
(defun eshell-fn-on-files (fun1 fun2 args)
(unless (null args)
(let ((filenames (thread-last args
(reverse)
(-flatten)
(-map 'file-expand-wildcards)
(-flatten))))
(apply fun1 (car filenames))
(when (cdr filenames)
(-map fun2 (cdr filenames))))))
#+end_src
This allows us to replace some of our aliases with functions:
The [[https://github.com/mathiasdahl/shell-underscore][shell-underscore]] project looks pretty cool, where the =_= character represents a /filename/ with the contents of the previous command (you know, like if you were planning on it, you’d =tee= at the end of every command). An interesting idea that I could duplicate.
While diving into the =eshell= source code, I noticed that the special variable, =$$= can be used /sometimes/ as the output of the last command. For instance:
#+begin_example
$ echo "hello world"
hello world
$ echo $$
hello world
#+end_example
However, what I would like is something like this to work:
#+begin_example
$ ls *.org(U)
a.org b.org f.org
$ rg "foobar" $$
#+end_example
The problem /may/ be between calling Emacs functions versus external commands, as the =echo= works, but the call to =ls= doesn’t:
#+begin_example
$ ls *.org(U) b.txt
a.org b.org f.org b.txt
$ echo Nam $$
("Nam" nil)
#+end_example
However, we could add a hook that runs /after/ every command to copy the output to a variables of our choosing:
#+begin_src emacs-lisp
(defvar OUTPUT ""
"Contains the output from the last eshell command executed.")
(defvar LAST nil
"Contains a list of elements from the last eshell command executed.")
Why three variables? Well unlike the behavior of the original shell (and most of its descendents, like =bash=), =eshell= doesn’t automatically split on whitespace. For instance, =echo= called this way:
Is given a list of /three elements/: =a=, =b=, and a list of all files in the current directory with an =.org= extension. An interesting side-effect is that spaces in filenames are /often okay/. So we want =$OUTPUT= to contain the command’s output /as a string/, and we have, =$LAST= contains the same stuff, but separated by spaces, into a list. So, if we are passing the output from =ls= to =grep=, we would use =$LAST= to represent files. And, like the =shell-underscore= project mentioned earlier, I may want to have the output stored in a file, so =$OUTAF= will hold this temporary filename… you know, /OUTput As a File/, right?
The following function does the work of saving the output of the last command. We can get this because after every command, eshell updates two variables, [[elisp:(describe-variable 'eshell-last-input-end)][eshell-last-input-end]] (the start of the output), and [[elisp:(describe-variable 'eshell-last-output-start)][eshell-last-output-start]] (the end of the output):
#+begin_src emacs-lisp
(defun ha-eshell-store-last-output ()
"Store the output from the last eshell command.
Called after every command by connecting to the `eshell-post-command-hook'."
Following [[http://blog.liangzan.net/blog/2012/12/12/customizing-your-emacs-eshell-prompt/][these instructions]], we build a better prompt with the Git branch in it (Of course, it matches my Bash prompt). First, we need a function that returns a string with the Git branch in it, e.g. ":master"
#+begin_src emacs-lisp :tangle no
(defun curr-dir-git-branch-string (pwd)
"Returns current git branch as a string, or the empty string if
PWD is not in a git repo (or the git command is not found)."
The function takes the current directory passed in via =pwd= and replaces the =$HOME= part with a tilde. I'm sure this function already exists in the eshell source, but I didn't find it...
#+begin_src emacs-lisp :tangle no
(defun pwd-replace-home (pwd)
"Replace home in PWD with tilde (~) character."
(interactive)
(let* ((home (expand-file-name (getenv "HOME")))
(home-len (length home)))
(if (and
(>= (length pwd) home-len)
(equal home (substring pwd 0 home-len)))
(concat "~" (substring pwd home-len))
pwd)))
#+end_src
Make the directory name be shorter...by replacing all directory names with just its first names. However, we leave the last two to be the full names. Why yes, I did steal this.
#+begin_src emacs-lisp :tangle no
(defun pwd-shorten-dirs (pwd)
"Shorten all directory names in PWD except the last two."
Some prompts, shells and terminal programs that display the exit code as an icon in the fringe. So can the [[http://projects.ryuslash.org/eshell-fringe-status/][eshell-fringe-status]] project. Seems to me, that if would be useful to rejuggle those fringe markers so that the marker matched the command entered (instead of seeing a red mark, and needing to scroll back in order to wonder what command it was that made it). Still...
#+begin_src emacs-lisp
(use-package eshell-fringe-status
:hook (eshell-mode . eshell-fringe-status-mode))
#+end_src
** Opening Banner
Whenever I open a shell, I instinctively type =ls= … so why not do that automatically? Perhaps we hook into the [[elisp:(describe-variable 'eshell-banner-load-hook)][eshell-banner-load-hook]]:
The only thing I would like is to not have the =ls= shown at the top of the buffer, nor added to the /history/. I’ll work on that some day.
* Shell Windows
Now that I often need to quickly pop into remote systems to run a shell or commands, I create helper functions to create those buffer windows. Each begin with =eshell-=:
** Shell There
The basis for opening an shell depends on the /location/. After that, we make the window smaller, give the buffer a good name, as well as immediately display the files with =ls= (since I instinctively just /do that/ … every time).
#+begin_src emacs-lisp
(defun eshell-there (parent)
"Open an eshell session in a PARENT directory
in a smaller window named after this directory."
(let* ((name (thread-first parent
(split-string "/" t)
(last)
(car)))
(eshell-buffer-name (format "*eshell: %s*" name))
(height (/ (window-total-height) 3))
(default-directory parent))
(split-window-vertically (- height))
(eshell)))
#+end_src
** Shell Here
This version of the =eshell= is based on the current buffer’s parent directory:
#+begin_src emacs-lisp
(defun eshell-here ()
"Opens up a new shell in the directory of the current buffer.
The eshell is renamed to match that directory to make multiple
eshell windows easier."
(interactive)
(eshell-there (if (buffer-file-name)
(file-name-directory (buffer-file-name))
default-directory)))
#+end_src
And let’s bind it:
#+begin_src emacs-lisp
(bind-key "C-!" 'eshell-here)
#+end_src
** Shell for a Project
I usually want the =eshell= to start in the project’s root, using [[help:projectile-project-root][projectile-project-root]]:
#+begin_src emacs-lisp
(defun eshell-project ()
"Open a new shell in the project root directory, in a smaller window."
(interactive)
(eshell-there (projectile-project-root)))
#+end_src
And we can attach this function to the =projectile= menu:
#+begin_src emacs-lisp
(ha-leader "p s" '("shell" . eshell-project))
#+end_src
** Shell Over There
Would be nice to be able to run an eshell session and use Tramp to connect to the remote host in one fell swoop:
#+begin_src emacs-lisp
(defun eshell-remote (host)
"Creates an eshell session that uses Tramp to automatically
connect to a remote system, HOST. The hostname can be either the
IP address, or FQDN, and can specify the user account, as in
root@blah.com. HOST can also be a complete Tramp reference."
Since I have Org files that contains tables of system to remotely connect to, I figured I should have a little function that can jump to a host found listed anywhere on the line.
The regular expression associated with IP addresses, hostnames, user accounts (of the form, =jenkins@my.build.server=, or even full Tramp references, is a bit...uhm, hairy. And since I want to reuse these, I will hide them in a function:
#+begin_src emacs-lisp
(defun ha-eshell-host-regexp (regexp)
"Returns a particular regular expression based on symbol, REGEXP"
The function to scan a line for hostname patterns uses different function calls that what I could use for =eshell-there=, so let's =save-excursion= and hunt around:
#+begin_src emacs-lisp
(defun ha-eshell-scan-for-hostnames ()
"Helper function to scan the current line for any hostnames, IP
or Tramp references. This returns a tuple of the username (if
found) and the hostname.
If a Tramp reference is found, the username part of the tuple
(let ((destination (ha-eshell-host->tramp user host (> p 1))))
(message "Connecting to: %s" destination)
(eshell-there destination))))
#+end_src
* Better Command Line History
On [[http://www.reddit.com/r/emacs/comments/1zkj2d/advanced_usage_of_eshell/][this discussion]] a little gem for using IDO to search back through the history, instead of =M-R= to prompt for the history.
#+begin_src emacs-lisp
(defun eshell-insert-history ()
"Displays the eshell history to select and insert back into your eshell."
(interactive)
(insert (completing-read "Eshell history: "
(delete-dups
(ring-elements eshell-history-ring)))))
#+END_SRC
* Command on the File Buffer
Sometimes you just need to change something about the current file you are editing...like the permissions or even execute it. Hitting =Command-1= will prompt for a shell command string and then append the current file to it and execute it.
#+begin_src emacs-lisp
(defun execute-command-on-file-buffer (cmd)
"Executes a shell command, CMD, on the current buffer's file.
If the filename is not specified, then it is appended to the cmd, so
chmod a+x
Works as expected. The special variable `$$' is replaced with the
filename of the buffer. Note that this is command is passed to
`eshell-command', so eshell modifiers are available, for
instance:
mv $$ $$(:r).txt
Will rename the current file to now have a .txt extension.
See `eshell-display-modifier-help' for details on that."
Here is where we associate all the functions and their hooks with =eshell=, through the magic of =use-package=.
Scrolling through the output and searching for results that can be copied to the kill ring is a great feature of Eshell. However, instead of running =end-of-buffer= key-binding, the following setting means any other key will jump back to the prompt:
#+begin_src emacs-lisp
(use-package eshell
:straight (:type built-in)
:init
(setq eshell-scroll-to-bottom-on-input 'all
eshell-error-if-no-glob t
eshell-hist-ignoredups t
eshell-save-history-on-exit t
;; Since eshell starts fast, let's get rid of it quickly:
eshell-kill-on-exit t
eshell-destroy-buffer-when-process-dies t
;; Can you remember the parameter differences between the
;; executables `chmod' and `find' and their Emacs equivalent? Me
;; neither, so this makes it act a bit more shell-like:
