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Working the Bash Shell Like a Pro

“People drive cars with steering wheels and gas pedals. Does that mean you don’t need wrenches?”
— Rob Pike

I’ve always preferred command-line interfaces (CLI) over GUIs. If I use GUIs at all then it’s mostly for browsing the web. Luckily, there is a plugin for my web browser that allows me to do most of my surfing using vi keystrokes. Yes, I try to avoid the mouse as much as I can.

I believe that most people who prefer GUIs either are bad at typing or haven’t taken the time to learn to use a CLI in an idiomatic way. With this post, I want to share some Bash CLI idioms that can significantly improve your efficiency. I don’t aim for a complete list — I rather present a compilation of the most frequently “not-known” techniques that I’ve encountered when I observed people working with Bash.


First of all, make sure that you have enabled the command-line editing mode that suits you best. You are much more productive when your favorite shortcuts are available:

Often, we need to do something that we’ve already done before. You can easily re-execute the previous command with this shortcut:

Courtesy of this operator, forgetting to put ‘sudo’ in front of a command is not a big deal:

If you want to re-execute “one of the previous commands” instead of the last one, you could use the following abbreviations:

However, I don’t find these history expansions particularly useful. Often, going through the history by pressing ‘Arrow Up’ is equally fast.

The real game changer, however, is CTRL-R. Press CTRL-R and start typing any characters from one of your previous commands. This will start a backwards search through your command-line history and present you with the most recent command containing the characters you typed (or continue to type). Pressing CTRL-R again will find the next most recent command and so on. If you only partly need what you typed in the past, no problem — you can always edit the command-line that CTRL-R found before executing it.


If you want to rename a file, please don’t do it like this:

Even with TAB completion, this requires too much typing. Why not reuse the path of the first argument?

‘!#’ is a shortcut for “the command-line typed so far” ‘:1’ selects the first argument and ‘:h’ strips off the last component (ie. “oldfile”).

In some cases, you don’t want to rename the file entirely but only change the extension. This can be achieved in a similar fashion:

You guessed it: ‘:r’ removes the file extension.

What if you did a mistake and wanted to undo this change? Again, that’s quite easy if you know the trick:

Which translates to “do another move but swap the arguments from the previous command”.

Sometimes, my fingers get ahead of me and I type ‘vm’ instead of ‘mv’:

Of course, you can always edit the last command be pressing ‘Arrow Up’ and change ‘vm’ to ‘mv’, but the following is much easier to type:

‘!*’ is a placeholder for “all arguments of the previous command”.

The word designator that I use the most — by far — is ‘!$’; it expands to the last argument of the last command:

Many times, people gratuitously reach for the mouse to copy the output of a previous command in order to use it as an argument for another command. Why not use ‘$()’ to capture command output?


If I was asked to name my favorite standard command-line tool, no doubt I would pick ‘xargs‘. Even though it is largely useless by itself, it’s the superglue that allowes you to build powerful command-lines. It takes the output of a command and uses it as arguments for another one.

Here’s an example that uses ‘xargs’ to build a tar archive containing all the C files that contain C++ comments:

In rare cases, when I have to do work that involves complicated selection/filtering, I reach out for TUI (usually ncurses-based) applications like ‘tig‘, ‘vifm‘, or ‘mc‘ that run in the shell and can be fully operated by the keyboard. Nevertheless, I first try to get by with the simpler ‘menucmd‘ tool. Here’s an example that builds a menu from all shell script files found in a directory. If the user selects an item, the specified action (‘cp -t /tmp’) is executed on it.

There you go. Even if this bag of tricks is not complete I hope it will serve you well. As always, in order to use a tool efficiently, you have to invest in learning how to use it idiomatically*. But this investment pays nice dividends in the medium-to-long term.

*) What’s the idiomatic way for vi users to underline a headline? 1. Yank the headline (‘yy’). 2. Paste the yanked headline under the exiting headline (‘p’). 3. Select the second headline (‘V’). 4. Replace every character in selected line with an underscore (‘r-‘) — that’s only six keystrokes! Awesome!

Why I don’t Use Apple Products

Every now and then, people ask me why I steer clear of iThings. Explaining my view over and over again is tedious, so I’ve decided to present my reasons in writing. When this topic comes up next time I just need to point people to this post, which will save a lot of time on both sides.

Open-source veteran Richard Stallman, founder of GNU and the Free Software Foundation (FSF) has already contributed his share to the topic. I do agree with most of his arguments but I still want to tell the story from my point of view.

First of all, let me emphasize that it has not always been like that. As a matter of fact, I used to be an Apple fan myself, even though this was in the early 1980s. My first home computer was an Apple II clone and I badly wanted to own a real Apple II, I can tell you. Alas, it was too expensive for an eighth grader’s measly monthly allowance.
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Two German Maxims That Will Save Your Neck (and Others’ Necks as Well)

I quite remember the uneasy sensation that I had when a former coworker told me a story — a story about a senior engineer who went to jail because of a bug, a fatal one, as it turned out.

The bug lurked in an electronic control unit (ECU) which was, among other things, controlling the manual deactivation of the front passenger seat’s airbag. Under normal circumstances, you wouldn’t want to disable an airbag, a feature that saves lives every day around the world. However, if you intend to put a rearward-facing baby seat in the front, you have to do it, or you risk severe injury of your child in case the airbag deploys during an accident.

Now, this unfortunate engineer discovered that under extremely rare conditions there was a tiny window of opportunity for the airbag deactivation mechanism to fail silently; that is, it would appear to be deactivated when in fact it wasn’t. I don’t remember the necessary prerequisites, but what I do remember is that the combination of inputs and actions sounded so silly, so unusual, so improbable that he — like probably most of us would have — expected that the fault would never ever show up in practice. But what a terrible mistake this was, as this is exactly what happened and a child lost its life.

How unlikely or likely is the higly improbable? The chances of winning a 6-number lottery game are typically 1 against many tens of millions; yet, the likelihood that some player (not a particular player, of course) wins is quite high. Why? Because there are millions of players who take part in such lotteries. The same is true for ECUs which frequently find their way into millions of cars.

The developer was punished not for creating the bug but for not telling his managers about his discovery, for keeping it secret. But why didn’t he report the problem to his superiors? I can only guess. Maybe there was a lot of schedule pressure, perhaps he didn’t want to upset his boss. Or, the product was already released and a recall would have cost a lot of money, let alone reputation. If you ask me, it was a deadly cocktail of fear and pride.

When I did my military training at the German Armed Forces, one of the first rules I learned was “Melden macht frei”, which more or less translates to “reporting is liberating”. It is your duty to report an incident and it has a liberating effect on you, both emotionally and legally. After reporting, it is your superior’s problem. He has to decide what to do next. That’s not dodging responsibility — it’s passing on an issue that is outside your area of responsibility to the right person.

In the same spirit, as professionals we also have to report any issue that is harmful to customers or the company, regardless of how unlikely it appears to us. Even if management makes a (hopefully prudent) decision to ignore the problem (like it was the case in the Space Shuttle Challenger disaster, where engineers clearly raised their concerns that the O-rings on the rocket boosters would not seal at low temperatures), at least you have behaved professionally and are saved from prosecution and guilt feeling.

There is, however, a strange phenomenon: People sometimes forget that you informed them, especially when they have to testify in court. That’s why I want to share another important German wisdom with you: “Wer schreibt, der bleibt”, which can be translated as “you write, you stay”. It means that (only) if you write something down, you will be remembered. In other words: always keep a paper trail; email usually suffices.

The Game of Life


“Imagine there’s no heaven
It’s easy if you try
No hell below us
Above us only sky”

— John Lennon “Imagine”

Once again, like every year, time has come to celebrate Towel Day, a great occasion to ponder Life, the Universe and Everything.

Speaking of Life — a surprising number of people, including software developers, don’t know about LIFE, also called Conway’s Game of Life; an even smaller number is aware of the corollaries, let alone accept them as a fact of life (pun intended!). So what is LIFE?

In LIFE, which isn’t really a game, but rather a simulation, there is an infinite field of cells; cells can be in either of two states: dead or alive. Conway defined four simple rules:

  1. A live cell with fewer than two live neighbors dies (think: dies of loneliness).
  2. A live cell with two or three live neighbors continues to live.
  3. A live cell with more than three live neighbors dies (think: dies of overpopulation).
  4. A dead cell with exactly three live neighbors becomes a live cell (think: birth of a cell).

You start with an initial (e.g. random) set of live and dead cells, let time increase in discrete steps and after every step you apply these four rules. That’s all. After every step the board contains a new set of live and dead cells.

It is quite fascinating to see how structures, patterns (or objects) emerge, move, disappear and reappear. Some of these objects have been given names that aptly describe their nature, like “pulsars”, “gliders”, “glider guns”, just to name a few.

What is even more fascinating is that these objects are governed by higher-order “laws” that are not obvious from the four simple rules. For instance, you can observe that “blocks” never move, “gliders” always move diagonally and “lightweight spaceships” always move from right to left. (Here is a great site for trying out various patterns yourself.)

Isn’t this very much like our own universe? In our universe, we have some fundamental laws, which give rise to higher-level structures and laws, up to highest-level laws of physics or principles of human behavior.

What Conway proved was that complex structures can emerge from simple rules; he proved that you don’t need a Creator to obtain a complex universe, just simple rules, time and favorable circumstances.

Religious people often have a hard time accepting that. One the one hand, they argue, Conway didn’t prove the absence of a Creator, and second, Conway himself acted as a Creator himself since he — after all — created the rules of the game. Isn’t there, in our world, at least room for such a “Creator of Rules”?

Nobody knows, but I personally don’t think so. What Conway did was not create the rules — he rather zoomed in on a particular universe with a particular rule set, chosen from an infinite set of rules: He just shed light on one particular universe that is favorable of life in an infinite multiverse.

Let me close this post with the words of Stephen Hawking. Like all human beings, he doesn’t know everything, but he is probably one of the persons who has the best grasp of our universe:

“We are each free to believe what we want and it is my view that the simplest explanation is there is no God. No one created the universe and no one directs our fate. This leads me to a profound realization. There is probably no heaven, and no afterlife either. We have this one life to appreciate the grand design of the universe, and for that, I am extremely grateful.”

The Reason We Have a Job

“There’s truths you have to grow into.”
― H.G. Wells, Love and Mr. Lewisham

Let me ask you a simple question. Why do you have a job?

Maybe you are convinced that you have a job because you have a lot of obligations, like hungry mouth to feed and bills to pay. Or because someone told you that every decent citizen simply must have a job these days.

But no, that’s not the answer I am looking for. These are all valid reasons why you want or need or should have a job.

Or maybe you believe the reason is that you are such an irresistibly smart person that every company just wants to posses.

No, again, such factors only make you attractive to your employer, they give you a competitive edge over other people.

So what is the real reason you have a job? Here is my answer: unless you work for a non-profit organization (or the government) the only reason why you have a job is that someone — the business owner — believes that, overall, you generate much more money than you cost.

The verb believes is essential here. It could be that you, objectively, turn out not to be such a great investment for your company, maybe even a massive waste of money, but that doesn’t matter much: you can still keep your job as long as your boss’ belief in your money-generating abilities remains strong.

However, once this belief (or hope) is gone, your days are numbered. You may stay on the payroll for quite some time, but you will be walking around neither dead nor alive, just like a zombie. The question is not if you will lose your job — the question is when.

But how cruel are these greedy company owners? What about social responsibility? Is it always just about the money?

This attitude arises from a common misconception, and yes, it is always just about the money. It is not the responsibility of a business owner to make employees rich (not even happy) — it is just the other way around. Sure, there are hip companies which treat their employees extremely well, pay high salaries and grant extraordinary benefits; but let’s not forget: it is only because there is (still) an enormous belief in a high return on investment. If everything turns out well in this gamble there is a win-win situation: happy business owner, happy employees — all the ingredients for a long-lasting virtuous circle.

In the not-so-fortunate case — and every company will face stormy weather, even the hippest — a business owner has to eliminate cost to ensure that his business stays profitable; not performing these life-saving amputations would put his and his employees’ future at risk. Unprofitable companies cannot exist for an extended period of time in a free market; they will sooner or later be eaten by the competition. And that’s not a statement — that’s a fact.

So wise developers should avoid becoming dependent on an employer’s dreams and beliefs. Instead, developers should constantly and aggressively invest in their knowledge portfolio and keep their resume up-to-date. They should neither mentally nor financially become too attached to a company or technology. Instead, they should always be ready to move on.

Give an outstanding performance for your money, but treat every day as if it would be your last. Get rid of those personal items on your desk. Accept that employments are transient. This not only gives you independence and self-confidence, it also makes you indispensable for your current employer — and your next.

Growing a Solid Software Company — Update

Yesterday, on October 21, all Lufhansa pilots went on strike in Germany. Nevertheless, Lufhansa managed to conduct half of their flights. They achieved this miracle by using a two-fold strategy: subcontractors and — lo and behold — their own managers, who, according to Lufthansa, work in most cases as part-time pilots, anyway.

Pilots that manage, managers that fly. Exactly my words, friends, exactly my words…

Let’s sing a song together, shall we?

I see trees of green, red roses, too,
I see them bloom, for me and you
And I think to myself
What a wonderful world.