Irreal

Álvaro Ramírez points out that Emacs has the built-in capability to calculate the number of days between two dates. It’s easy to do; the tl;dr is:

M-x calendar
<mark the region between the two dates (inclusive)>
M-= (or M-x calendar-count-days-region)

Ramírez has some animated screen shots that show how it works and also a shortcut for going to the endpoints of the date range.

It’s a nice trick and it’s all already there. Read the post and try it out.

This is exactly how I think of Emacs

"Emacs is a Lisp VM with built in primitives for handling its fundamental data structure – buffers (of mostly, but not always text.)"

— unbalancedparen (@unbalancedparen) May 13, 2016

It’s almost a cliché but Emacs really is much more than an editor. It’s the way I organize my workflow.

The other day I wrote about using the SIGUSR2 signal to quit Emacs. It’s usually enough to unjam Emacs and get you into a state where you can at least save your work and restart Emacs.

Marcin Borkowski (mbork) has a very nice post that explores the use of SIGUSR2 and how it interacts with the debugger. If you’re developing in Elisp and often find yourself hung, some of mbork’s techniques may help you figure things out. It’s an informative post and well worth taking a look at.

Howard Abrams has a nifty video on his setup for invoking remote shells. Those of you who have followed his recent videos know that he works with a lot of virtual machines and it is convenient for him to be able to swiftly connect to them—from within Emacs, of course.

To do that he first builds a hash table (this happens automatically) mapping host nickname to IP address or fully qualified domain name. Then he does a completing read to get the nickname, and hence the IP address or FQDN, of the host he wants to connect to. The rest is easy: he essentially executes the code

(defun remote-host (host)
  (let ((default-directory (format "/%s:" host)))
    (shell host)))

where host is the result of the hash table mapping.

Notice the nice trick here. By setting default-directory to a remote host, tramp is automatically invoked and you’re running a shell on the remote machine. By setting default-directory to something like /ssh:host|sudo:host: you can invoke the shell as root. See Abrams’ code for the details.

Naturally, his setup is a little more complex but this captures its essence. He also has a function to run a command on a remote host using the same strategy but calling shell-command instead of shell. He even shows how to run the same command on a list of remote hosts all automatically. You can see how this would be useful if you’re administering several machines.

In the video, he doesn’t spend a lot of time going over the code so you’ll want to check it out at on his github. The video is only 6 minutes 42 seconds so you can enjoy it during a coffee break. Highly recommended.

UPDATE [2016-05-13 Fri]: Fixed link to the github code. Abrams → Abrams’.