Don't yell at your colleagues; yell in your shell

You and I are probably very different; my choice of editor is likely to
make you cringe just thinking about it, and your favorite programming language
is statistically — definitely — not mine.

There is however one thing (and maybe that's the only thing) we all have in common; we are a bunch of lazy bastards.

Note: This article is primarily targetingbash,csh,tcsh, andzsh. If these shells are not your daily driver, see POSIX and the power offc— worth a read no matter which POSIX-compatible shell you use.

Command-line repetition we socially accept

$ ssh some-user@10.240.33.109 $ echo "done with some-user@10.240.33.109" >> ~/work/superfun-client/worklog $ cd ~/work/superfun-client && cat TODO $ ssh some-user@10.240.33.109 # <- forgot something
I am sure we have all ended up in arrow-up-mashing hell when repeating commands in our shell history, but what if we instead could save ourselves the trouble and refer to previous commands and their arguments directly?

$ ssh some-user@10.240.33.109 $ echo "done with !:1" >> ~/work/superfun-client/worklog $ cd !$:h && cat TODO $ !ssh
No yelling — just exclamation marks.

Note: The magic described in this article applies to interactive shells unless configured otherwise, it isnotmeant to be used in your newamazing.shshell script.

Don't Repeat Yourself.

I bet you've heard it before, "do not repeat yourself", either from that
annoying colleague with all the obscure magic (who might smell a little funny) —
or perhaps you said it yourself during the last refactor session that somehow
lasted longer than the federation delay on matrix.org.

$ apt install awesome-package # insufficient permissions $ sudo !! # repeat with sudo
$ mkdir /var/mnt/cache # the usual create directory dance $ cd !$ # cd to the directory, no finger strain needed
Most of us have heard DRY repeated since we were ki–, I mean junior. But is it not funny that we've religiously been taught to apply DRY everywhere… except on the command‑line?

$ touch ~/projects/work/awesome.sh $ cd !$:h # cd to the directory of awesome.sh
$ ssh 10.240.33.109 -p2222 -i ~/.ssh/prod/ed25519 $ ssh 10.240.33.110 !:2* # same flags, another host
$ ffmpeg -i /recordings/a-sunny-day.mov !#:2:r.mkv ffmpeg -i /recordings/a-sunny-day.mov /recordings/a-sunny-day.mkv $ scp !$:r.* example.com:/media scp /recordings/a-sunny-day.* example.com:/media

        What is ~~ this magic ~~ an event designator?

Even though they might look mighty daunting at first glance, event designators always follow the same rather simple pattern:

![event][:word][:modifier] | | | | | '--> modifier [ :h :t :r :e ... ] | '-----------> which part [ :0 :$ :* :2-3 ... ] '------------------> which line [ !! !-2 !ssh !?needle? ... ]

Note: Want to know the bare necessities? Check out yell responsibly for the 4 event designators I consider most useful.

Note: Already fluent? Skip to posix and the power offcfor one of the most useful albeit niche commands I have ever had the pleasure of running — who haven't wished they could edit their long commands in an editor rather than in the shell?

Event Designator

The first part immediately following the exclamation mark denotes which lines we are interested in — here are a few examples which will effectively rerun the referred to command:

$ !! # the previous line $ !-2 # two lines back $ !1337 # the 1337th line, as displayed by `history` $ !ssh # the most recent line starting with "ssh" $ !?dandelion? # the most recent line containing "dandelion" $ !# # the current line, written so far $ ^ssh^scp^ # replace first ssh with scp in previous command

Note: If the!is immediately followed by:, no explicit event is specified and the expression will refer to the immediately previous line.

Word Designator

After the event designator (if any) you may specify which part of the line
you are interested in. All examples below are written as if they follow the
command in the first code block.

$ /path/to/script.sh "hello world" --enable 1337
$ !:0 # 1st word --> "/path/to/script.sh" $ !:1 # 2nd word --> "hello world" $ !:$ # last word --> "1337"
$ !:1-2 # 1st to 2nd --> "hello world" "--enable" $ !:* # all args --> "hello world" "--enable" "1337" $ !:1- # all but last --> "hello world" "--enable" $ !:2* # 3rd to last --> "--enable" "1337"

Note: There are several short-form expressions that work without even specifying a colon, like!$being equivalent to!:$,!*being equivalent to!:*, and so forth.

Modifier

Modifiers are perhaps where we enter "oh-daaaaaaaym"-territory — they allow
you to extract/modify only certain parts of what would otherwise be an entire
argument.

$ !:$:h # strip filename (`dirname`) $ !:1:t # strip leading path (`basename`) $ !:1:r # strip only the extension $ !:1:e # leave only the extension
$ !:s/hello/bye/ # replace first 'hello' with 'bye' $ !:gs/foo/bar/ # replace all 'foo' with 'bar'
$ !ssh:p # print what would run, without running it

        POSIX and the power of `fc`

Whether or not your shell speaks !, fc belongs in your imaginary tool belt.
It can be used to repeat the previous command, but the true power lies in the
fact that you can edit your command-line not in your shell — but in your editor
of choice.

Every shell adventurer should run fc at least once a year, if only to marvel
at its usability:

$ fc # edit the previous command $ fc -2 # edit the command 2 steps back $ fc grep # edit last command starting with grep
$ fc -3 -1 # the last three commands, all in one buffer $ fc ssh -1 # from the last 'ssh' line through the most recent one
$ fc -s ssh # repeat last command starting with 'ssh' $ fc -s hello=world ssh # replace "hello" with "world" on the line starting with 'ssh'
fc will invoke whatever program is specified in $FCEDIT to do the editing,
if no such specification exists POSIX falls back to ed — though many shells
will default to $EDITOR.

You may also specify which editor to invoke using -e:

$ scp api.tar.gz prod-01:/tmp $ ssh prod-01 systemctl restart api $ curl -sf https://prod-01/health
$ fc -e 'sed -i s/prod-01/test-01/g' -3 -1
The above will rerun all three commands, replacing prod-01 with test-01 in
each; a contrived example perhaps but man is it useful when you find yourself in
such trouble.

Note

fclives in the User Portability Utilities of POSIX.- Truly minimal shells like
dashand busyboxashship without it entirely.

Yell responsibly

Event designators, or fc in the case of POSIX, are not going to change your
life and turn you into an über-10x-developer-always-wearing-a-hoodie; they might
however save you anywhere between four and forty-two keystrokes at a time, a few
hundred times a week, over the many years spanning your career.

For what it's worth, it is often enough to simply remember four of them:

• !$the last argument of the previous command
• !:0when you need to rerun that annoyingly located script again
• !$:hfor an easy extraction of the directory part
• !$:tfor when you want the filename and nothing else

We might yell at each other when discussing the best editor, but in our shells we may forever whisper:

• "I am lazy, and the exclamation mark is my weapon".

Frequently Asked Questions

If you have a question or feedback of your own, please feel free to shoot me an email at filip.roseen@atch.se.

• Why not use- ctrl-rinstead of memorizing a bunch of things?- ctrl-r, a.k.a. command-line history search, is extremely powerful, but it will at best give you a template to modify;- event designatorsallow you to extract partial contents.- Also, why search if you already know what you want to run? - !sshvs- ctrl-r+- ssh— the former is also kinda cooler™.

• Why not use- alt-.instead of- !$?- alt-.is great for what it is designed to do, iterating over the previous "last arguments" of your shell history. It's great at doing that, but it is also limited to doing just that- onething.

• Are you not disregarding other useful features?- I am not aiming for some sort of "either or" situation when I publish my articles — whatever gets the work done is what you should use. - And for what it's worth… never do what a stranger tells you online; personal preference and workflows are worth more than any article (no matter the amount of obscure sometimes forgotten magic).

• !just gets in the way, how do I turn this off?- I bet many have been bitten by the "usability" of event designators without realizing what they are for, such as in the example below: - $ echo "!dlrow olleh" bash: !dlrow: event not found- If you would like to turn things off so that you can use - !anywhere, you may use- set +Hin- bashand- setopt nobanghistin- zsh; for other shells I recommend consulting your manual.- You may also go full smelly-colleague-with-magic (please wear deodorant in public), and instead use any character of your liking: - $ histchars='%^#' # event-trigger, substitution, comment $ echo "hello world" hello world $ echo %$:s/world/the internet/ hello the internet- Remember to put your configuration in the relevant dot-rc file to make the changes persistent.

Further Reading

Other articles in this series:

Documentation relevant to event designators: