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hamacs/ha-eshell.org
Howard Abrams 334c3f9cff Access past version's of eshell command output 
Simple addition of some rings to store a bit of eshell command
history. I really can't believe how easy this stuff is to write.
2022-09-23 21:56:49 -07:00

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#+TITLE: Eshell
#+AUTHOR: Howard X. Abrams
#+DATE: 2022-09-13
#+FILETAGS: :emacs:
A literate programming file for configuring the Emacs Shell.
#+begin_src emacs-lisp :exports none
;;; ha-eshell --- Emacs Shell configuration. -*- lexical-binding: t; -*-
;;
;; © 2022 Howard X. Abrams
;; This work is licensed under a Creative Commons Attribution 4.0 International License.
;; See http://creativecommons.org/licenses/by/4.0/
;;
;; Author: Howard X. Abrams <http://gitlab.com/howardabrams>
;; Maintainer: Howard X. Abrams
;; Created: September 13, 2022
;;
;; While obvious, GNU Emacs does not include this file or project.
;;
;; *NB:* Do not edit this file. Instead, edit the original literate file at:
;; /Users/howard.abrams/other/hamacs/ha-eshell.org
;; And tangle the file to recreate this one.
;;
;;; Code:
#+end_src
* Introduction
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."
(interactive "p")
(if (and (eolp) (looking-back eshell-prompt-regexp))
(progn
(eshell-life-is-too-much) ; Why not? (eshell/exit)
(ignore-errors
(delete-window)))
(delete-forward-char arg)))
#+END_SRC
** Pager Setup
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
(let ((ls (if (file-exists-p "/usr/local/bin/gls")
"/usr/local/bin/gls"
"/bin/ls")))
(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:
(if (looking-at (rx "'" (group (one-or-more (not (or ")" "'"))))"'"))
(let* ((tag (match-string 1))
(reg (rx line-start
"#+" (optional "file") "tags:"
(one-or-more space)
(zero-or-more any)
(literal tag) word-end)))
(goto-char (match-end 0))
;; Step 2. Return the predicate function:
;; Careful when accessing the `reg' variable.
`(lambda (file)
(with-temp-buffer
(insert-file-contents file)
(re-search-forward ,reg nil t 1))))
(error "The `T' predicate takes an org-mode tag value in single quotes.")))
#+END_src
Then we need add that function to the =eshell-predicate-alist= as the =T= tag:
#+begin_src emacs-lisp
(defun ha-eshell-add-predicates ()
"A hook to add a `eshell-org-file-tags' predicate filter to eshell."
(add-to-list 'eshell-predicate-alist '(?T . (eshell-org-file-tags))))
#+end_src
*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.
** Map
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.
** Git
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:
#+begin_src emacs-lisp
(defun eshell/e (&rest args)
"Edit one or more files in current window."
(eshell-fn-on-files 'find-file 'find-file-other-window args))
(defun eshell/ee (&rest args)
"Edit one or more files in another window."
(eshell-fn-on-files 'find-file-other-window 'find-file-other-window args))
#+end_src
We’ll leave the =e= alias to replace the =eshell= buffer window.
** Last Results
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.")
(defvar OUTAF ""
"Contains a filename that contains the output from the last eshell command.")
#+end_src
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:
#+begin_example
$ echo a b *.txt
("a" "b"
("b.txt" "date today.txt"))
#+end_example
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'."
(setq OUTPUT
(s-trim
(buffer-substring-no-properties eshell-last-input-end eshell-last-output-start)))
(setq OUTAF (make-temp-file "ha-eshell-"))
(setq LAST (split-string OUTPUT))
;; Put the three values in the historical rings (see below):
(ha-eshell-store-output-history OUTPUT LAST OUTAF)
(ring-insert (gethash :text ha-eshell-output) OUTPUT)
(ring-insert (gethash :list ha-eshell-output) LAST)
(ring-insert (gethash :file ha-eshell-output) OUTAF)
(with-temp-file OUTAF
(insert OUTPUT)))
#+end_src
Now we save this output after every command by adding it to the [[elisp:(describe-variable 'eshell-post-command-hook)][eshell-post-command-hook]]:
#+begin_src emacs-lisp
(add-hook 'eshell-post-command-hook 'ha-eshell-store-last-output)
#+end_src
Success:
#+begin_example
$ ls *.org(U) b.txt
a.org b.txt
$ rg Nam $LAST
a.org
8:Nam vestibulum accumsan nisl.
b.txt
1:Nam euismod tellus id erat.
#+end_example
*** Accessing Output from the Past
It would also be great if you could grab /historical/ versions of those output. Instead of storing two or three objects to hold them, what about a hash table as a single interface?
#+begin_src emacs-lisp
(defvar ha-eshell-output (make-hash-table :size 3)
"A collection of rings representing the various historical output")
#+end_src
How would we store the historical lists? This is what [[info:elisp#Rings][rings]] are for:
#+begin_src emacs-lisp
(puthash :text (make-ring 10) ha-eshell-output)
(puthash :file (make-ring 10) ha-eshell-output)
(puthash :list (make-ring 10) ha-eshell-output)
#+end_src
The [[help:ha-eshell-store-last-output][ha-eshell-store-last-output]] function calls this function in order to store the results in the three rings:
#+begin_src emacs-lisp
(defun ha-eshell-store-output-history (last-output last-list last-output-file)
"Store the LAST-OUTPUT as a string in a ring in the `ha-eshell-output'.
The LAST-LIST and LAST-OUTPUT-FILE are also store in separate rings."
(ring-insert (gethash :text ha-eshell-output) last-output)
(ring-insert (gethash :list ha-eshell-output) last-list)
(ring-insert (gethash :file ha-eshell-output) last-output-file))
#+end_src
How best to access this historical data. If there we some other shell, I might have variables like =$OUTPUT_3= or something. I think a function may be sufficient in practice. I’ll just call it [[help:eshell/output][output]] until something better comes along.
#+begin_src emacs-lisp
(defun eshell/output (frmt &optional element)
"Return an eshell command output from its history.
The FORMAT represents how the output should be returned, and must
be `:text', `:list' or `:file'. The ELEMENT is the index into the
historical past, where `0' is the most recent, `1' is the next oldest, etc."
(if-let ((ring (gethash frmt ha-eshell-output)))
(ring-ref ring (or element 0))
""))
#+end_src
How would this function work in practice?
#+begin_example
$ echo (output :text 0) # The same as echo $OUTPUT
#+end_example
A bit verbose. I think some syntactic sugar functions would be in order:
#+begin_src emacs-lisp
(defun eshell/output-t (&optional element)
(eshell/output :text element))
(defun eshell/output-l (&optional element)
(eshell/output :list element))
(defun eshell/output-f (&optional element)
(eshell/output :file element))
#+end_src
How would this look? Something like:
#+begin_example
$ cat (output-f 4)
#+end_example
The final trick is being able to count backwards and remember they are always shifting. I guess if I wanted to remember the output for more than one command, I could do:
#+begin_example
$ setq OUTPUT_A $OUTPUT
#+end_example
* Special Prompt
Following [[http://blog.liangzan.net/blog/2012/12/12/customizing-your-emacs-eshell-prompt/][these instructions]], we build a better prompt with the Git branch in it (Of course, it matches my Bash prompt). First, we need a function that returns a string with the Git branch in it, e.g. ":master"
#+begin_src emacs-lisp :tangle no
(defun curr-dir-git-branch-string (pwd)
"Returns current git branch as a string, or the empty string if
PWD is not in a git repo (or the git command is not found)."
(interactive)
(when (and (not (file-remote-p pwd))
(eshell-search-path "git")
(locate-dominating-file pwd ".git"))
(let* ((git-url (shell-command-to-string "git config --get remote.origin.url"))
(git-repo (file-name-base (s-trim git-url)))
(git-output (shell-command-to-string (concat "git rev-parse --abbrev-ref HEAD")))
(git-branch (s-trim git-output))
(git-icon "\xe0a0")
(git-icon2 (propertize "\xf020" 'face `(:family "octicons"))))
(concat git-repo " " git-icon2 " " git-branch))))
#+end_src
The function takes the current directory passed in via =pwd= and replaces the =$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."
(let ((p-lst (split-string pwd "/")))
(if (> (length p-lst) 2)
(concat
(mapconcat (lambda (elm) (if (zerop (length elm)) ""
(substring elm 0 1)))
(butlast p-lst 2)
"/")
"/"
(mapconcat (lambda (elm) elm)
(last p-lst 2)
"/"))
pwd))) ;; Otherwise, we just return the PWD
#+end_src
Break up the directory into a "parent" and a "base":
#+begin_src emacs-lisp :tangle no
(defun split-directory-prompt (directory)
(if (string-match-p ".*/.*" directory)
(list (file-name-directory directory) (file-name-base directory))
(list "" directory)))
#+END_SRC
Using virtual environments for certain languages is helpful to know, especially since I change them based on the directory.
#+begin_src emacs-lisp :tangle no
(defun ruby-prompt ()
"Returns a string (may be empty) based on the current Ruby Virtual Environment."
(let* ((executable "~/.rvm/bin/rvm-prompt")
(command (concat executable "v g")))
(when (file-exists-p executable)
(let* ((results (shell-command-to-string executable))
(cleaned (string-trim results))
(gem (propertize "\xe92b" 'face `(:family "alltheicons"))))
(when (and cleaned (not (equal cleaned "")))
(s-replace "ruby-" gem cleaned))))))
(defun python-prompt ()
"Returns a string (may be empty) based on the current Python
Virtual Environment. Assuming the M-x command: `pyenv-mode-set'
has been called."
(when (fboundp #'pyenv-mode-version)
(let ((venv (pyenv-mode-version)))
(when venv
(concat
(propertize "\xe928" 'face `(:family "alltheicons"))
(pyenv-mode-version))))))
#+end_src
Now tie it all together with a prompt function can color each of the prompts components.
#+begin_src emacs-lisp :tangle no
(defun eshell/eshell-local-prompt-function ()
"A prompt for eshell that works locally (in that is assumes
that it could run certain commands) in order to make a prettier,
more-helpful local prompt."
(interactive)
(let* ((pwd (eshell/pwd))
(directory (split-directory-prompt
(pwd-shorten-dirs
(pwd-replace-home pwd))))
(parent (car directory))
(name (cadr directory))
(branch (curr-dir-git-branch-string pwd))
(ruby (when (not (file-remote-p pwd)) (ruby-prompt)))
(python (when (not (file-remote-p pwd)) (python-prompt)))
(dark-env (eq 'dark (frame-parameter nil 'background-mode)))
(for-bars `(:weight bold))
(for-parent (if dark-env `(:foreground "dark orange") `(:foreground "blue")))
(for-dir (if dark-env `(:foreground "orange" :weight bold)
`(:foreground "blue" :weight bold)))
(for-git `(:foreground "green"))
(for-ruby `(:foreground "red"))
(for-python `(:foreground "#5555FF")))
(concat
(propertize "⟣─ " 'face for-bars)
(propertize parent 'face for-parent)
(propertize name 'face for-dir)
(when branch
(concat (propertize " ── " 'face for-bars)
(propertize branch 'face for-git)))
;; (when ruby
;; (concat (propertize " ── " 'face for-bars)
;; (propertize ruby 'face for-ruby)))
;; (when python
;; (concat (propertize " ── " 'face for-bars)
;; (propertize python 'face for-python)))
(propertize "\n" 'face for-bars)
(propertize (if (= (user-uid) 0) " #" " $") 'face `(:weight ultra-bold))
;; (propertize " └→" 'face (if (= (user-uid) 0) `(:weight ultra-bold :foreground "red") `(:weight ultra-bold)))
(propertize " " 'face `(:weight bold)))))
(setq-default eshell-prompt-function #'eshell/eshell-local-prompt-function)
#+end_src
Here is the result:
[[http://imgur.com/nkpwII0.png]]
** Fringe Status
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]]:
#+begin_src emacs-lisp :tangle no
(defun ha-eshell-banner (&rest ignored)
"My personal banner."
(insert "ls")
(eshell-send-input))
(add-hook 'eshell-banner-load-hook 'ha-eshell-banner)
(setq eshell-banner-message "")
#+end_src
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."
(interactive "sHost: ")
(let ((destination-path
(cond
((string-match-p "^/" host) host)
((string-match-p (ha-eshell-host-regexp 'full) host)
(string-match (ha-eshell-host-regexp 'full) host) ;; Why!?
(let* ((user1 (match-string 2 host))
(host1 (match-string 3 host))
(user2 (match-string 6 host))
(host2 (match-string 7 host)))
(if host1
(ha-eshell-host->tramp user1 host1)
(ha-eshell-host->tramp user2 host2))))
(t (format "/%s:" host)))))
(eshell-there destination-path)))
#+END_SRC
** Shell Here to There
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"
(let* ((user-regexp "\\(\\([[:alnum:]._-]+\\)@\\)?")
(tramp-regexp "\\b/ssh:[:graph:]+")
(ip-char "[[:digit:]]")
(ip-plus-period (concat ip-char "+" "\\."))
(ip-regexp (concat "\\(\\(" ip-plus-period "\\)\\{3\\}" ip-char "+\\)"))
(host-char "[[:alpha:][:digit:]-]")
(host-plus-period (concat host-char "+" "\\."))
(host-regexp (concat "\\(\\(" host-plus-period "\\)+" host-char "+\\)"))
(horrific-regexp (concat "\\b"
user-regexp ip-regexp
"\\|"
user-regexp host-regexp
"\\b")))
(cond
((eq regexp 'tramp) tramp-regexp)
((eq regexp 'host) host-regexp)
((eq regexp 'full) horrific-regexp))))
#+END_SRC
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
will be `nil'."
(save-excursion
(goto-char (line-beginning-position))
(if (search-forward-regexp (ha-eshell-host-regexp 'tramp) (line-end-position) t)
(cons nil (buffer-substring-no-properties (match-beginning 0) (match-end 0)))
;; Returns the text associated with match expression, NUM or `nil' if no match was found.
(cl-flet ((ha-eshell-get-expression (num) (if-let ((first (match-beginning num))
(end (match-end num)))
(buffer-substring-no-properties first end))))
(search-forward-regexp (ha-eshell-host-regexp 'full) (line-end-position))
;; Until this is completely robust, let's keep this debugging code here:
;; (message (mapconcat (lambda (tup) (if-let ((s (car tup))
;; (e (cadr tup)))
;; (buffer-substring-no-properties s e)
;; "null"))
;; (-partition 2 (match-data t)) " -- "))
(let ((user1 (ha-eshell-get-expression 2))
(host1 (ha-eshell-get-expression 3))
(user2 (ha-eshell-get-expression 6))
(host2 (ha-eshell-get-expression 7)))
(if host1
(cons user1 host1)
(cons user2 host2)))))))
#+end_src
Tramp reference can be long when attempting to connect as another user account using the pipe symbol.
#+begin_src emacs-lisp
(defun ha-eshell-host->tramp (username hostname &optional prefer-root)
"Returns a TRAMP reference based on a USERNAME and HOSTNAME
that refers to any host or IP address."
(cond ((string-match-p "^/" host)
host)
((or (and prefer-root (not username)) (equal username "root"))
(format "/ssh:%s|sudo:%s:" hostname hostname))
((or (null username) (equal username user-login-name))
(format "/ssh:%s:" hostname))
(t
(format "/ssh:%s|sudo:%s|sudo@%s:%s:" hostname hostname username hostname))))
#+end_src
Finally, a function to pull it all together.
#+begin_src emacs-lisp
(defun eshell-here-on-line (p)
"Search the current line for an IP address or hostname, and call the `eshell-here' function.
Call with PREFIX to connect with the `root' useraccount, via
`sudo'."
(interactive "p")
(destructuring-bind (user host) (ha-eshell-scan-for-hostnames)
(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 `$$' is replaced with the
filename of the buffer. Note that this is command is passed to
`eshell-command', so eshell modifiers are available, for
instance:
mv $$ $$(:r).txt
Will rename the current file to now have a .txt extension.
See `eshell-display-modifier-help' for details on that."
(interactive "sCommand to execute: ")
(let* ((file-name (buffer-file-name))
(full-cmd (cond ((string-match (rx "$$") cmd)
(replace-regexp-in-string (rx "$$") file-name cmd))
((string-match (rx (literal file-name)) cmd)
cmd)
(t
(concat cmd " " file-name)))))
(message "Executing: %s" full-cmd)
(eshell-command full-cmd)))
#+end_src
* Configuration
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:
eshell-prefer-lisp-functions nil)
:hook ((eshell-pred-load . ha-eshell-add-predicates)
(eshell-exit . delete-window))
:bind (:map eshell-mode-map
("M-R" . eshell-insert-history)
("C-d" . ha-eshell-quit-or-delete-char)))
#+end_src
Note that the default list to [[emacs-lisp:(describe-variable 'eshell-visual-commands)][eshell-visual-commands]] is mostly good enough.
Finally, add some leader commands to call my previously defined functions:
#+begin_src emacs-lisp
(ha-leader
"a e" '(:ignore t :which-key "eshell")
"a e e" '("new eshell" . eshell-here)
"a e r" '("remote" . eshell-remote)
"a e p" '("project" . eshell-project)
"a e g" '("at point" . eshell-here-on-line)
"a e !" '("exec on file-buffer" . execute-command-on-file-buffer))
#+end_src
No, i’m not sure why =use-package= has an issue with both =:hook=, =:bind= and =:config= directives in sequence.
* Technical Artifacts :noexport:
Let's =provide= a name so we can =require= this file:
#+begin_src emacs-lisp :exports none
(provide 'ha-eshell)
;;; ha-eshell.el ends here
#+end_src
#+DESCRIPTION: Emacs configuration for the Emacs Shell.
#+PROPERTY: header-args:sh :tangle no
#+PROPERTY: header-args:emacs-lisp :tangle yes
#+PROPERTY: header-args :results none :eval no-export :comments no mkdirp yes
#+OPTIONS: num:nil toc:nil todo:nil tasks:nil tags:nil date:nil
#+OPTIONS: skip:nil author:nil email:nil creator:nil timestamp:nil
#+INFOJS_OPT: view:nil toc:nil ltoc:t mouse:underline buttons:0 path:http://orgmode.org/org-info.js
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