147 lines
6.5 KiB
Markdown
147 lines
6.5 KiB
Markdown
2022-05-29
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# The Joy of One-Liners
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There is an engineering idiom which withstands time like no other. As
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old as the hills but never forgotten. In informational technology
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relations, one could say it is ancient. Its dawn proclaimed from the
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shores of Seattle, defeated by an apocalyptic horseman with the
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melodious name *NT*. Shot! Point blank into the chest. Buried under the
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hills of an IT dark age which we call the nineties, dead. But is it?
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Well, not exactly. There is still life in the old dog. Like Beatrix
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Kiddo, it one-inch punches itself back to daylight. Coal black as a
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miner. Topsoil sticks to its beige 1978's leather jacket, it trickles to
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the ground with every step taken to the nearest diner. The door opens
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again. "May I have a glass of water, please?"
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An art passed down from the ancestors. Its most visible interface: *The
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Shell*. Its name: *The Unix Philosophy*.
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Coined by Doug McIlroy in the [Bell System Technical
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Journal](https://archive.org/details/bstj57-6-1899/mode/2up) as a
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foreword to the UNIX Time-Sharing System. There is an even more concise
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version[[1]](#references) and
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according to [Eric Steven
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Raymond](http://www.catb.org/~esr/writings/taoup/html/ch01s06.html) this
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is [[2]](#references):
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> "This is the Unix philosophy: Write programs that do one thing and do
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> it well. Write programs to work together. Write programs to handle
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> text streams, because that is a universal interface."
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> --- Doug McIlroy ---
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In some way, this is similar to the concept of the on vogue philosophy
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of microservices everywhere. Services are written to do one thing and do
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it well. They work together. Also, text is the connecting link between
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programs, services, and humans. The possibility to read a program's
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output as text seems benign, as long as everything is working well. The
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advantage is interactivity at any time, testability of every component,
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and debuggability at every step of the process in an on the fly manner.
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Impromptu, out of reflex like a punch.
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## [Pipe Dreams](#pipe-dreams)
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------------------------------------------------------------------------
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Mc Ilroy made another very important contribution, which is the Unix
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pipe. It is the practical implementation of connecting the programs
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inside the shell. He saw the programs as tools, plugged together via
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pipes building a
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[toolbox](http://www.princeton.edu/~hos/Mahoney/expotape.htm). Program
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A's `stdout` is put into the `stdin` of program B. This leaves us with a
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single line of chained, well-defined programs to solve a problem that
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would otherwise be an extensive, multi-line program in any programming
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language of your choice.
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Let's say we've got two programs. The first is one is *fortune*, the
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fortune cookie program from BSD games, which outputs random quotes as
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text. The second one is *cowsay*, which displays various kinds of
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animals as ASCII art. In order to work in a coherent manner a `|` is
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used. The pipe connects the first one to the second one.
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```sh
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fortune | cowsay
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_________________________________________
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/ Gil-galad was an Elven-king. Of him the \
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| harpers sadly sing: the last whose |
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| realm was fair and free between the |
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| Mountains and the Sea. |
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| |
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| His sword was long, his lance was keen, |
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| his shining helm afar was seen; the |
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| countless stars of heaven's field were |
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| mirrored in his silver shield. |
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| |
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| But long ago he rode away, and where he |
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| dwelleth none can say; for into |
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| darkness fell his star in Mordor where |
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| the shadows are. |
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\ -- J. R. R. Tolkien /
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-----------------------------------------
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\ ^__^
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\ (oo)\_______
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(__)\ )\/\
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||----w |
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|| ||
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```
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To mix in some colors pipe everything through lolcat. Try it out!
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```sh
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fortune | cowsay | lolcat
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```
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So far so good, let us gain some real-world practice.
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## [Punching Lines and Retire Your Password Generator](#punching-lines-and-retire-your-password-generator)
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------------------------------------------------------------------------
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Have you ever questioned the integrity of your one-click, GUI,
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proprietary password generator? Is its randomness really as
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unpredictable as it proclaims? Are you the only one which ends up
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knowing your generated password? There is a one-liner that ups your
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opsec instantly. Right from the source of randomness:
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```sh
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head -n 42 /dev/urandom | tr -cd '[:alnum:]' | cut -c-12
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```
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So, what is going on here? Everything is a file, that is the way \*nix
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systems see it, even the device which puts out random data. To read the
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upper part of a file we use `head`. It will be sent to `stdout` and
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displayed via the shell. Parameter `-n` reads exactly 42 lines of the
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file given to gather enough randomness. The output of `head` will be
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sent to `tr`. In order to select only alphanumeric characters for our
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password, we use `'[:alnum:]'`. Parameters `-c` selects the complement
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of alphanumeric characters and `-d` deletes them. `cut` does exactly
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what it says, `-c-12` cuts after 12 characters with leaves us with a
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random password of length 12. Every time you execute this one-liner a
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freshly made random password is returned.
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To extend the pool of possible symbols the manual of `tr` lists various
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sets of filtered symbols. In the case of a password generator, further
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sensible filters are `'[:alpha:]'` or `'[:digit:]'`. While `'[:graph:]'`
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is also viable in this case it returns one of the greater sets of
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symbols. Use it with caution, especially if you create passwords for
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database users. These might be terminated prematurely through `` ` `` or
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`'` inside the returned string.
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## [Sunday Punch](#sunday-punch)
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------------------------------------------------------------------------
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This blog entrance can be seen as a prelude to a series of one-liners I
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use time and time again. The are multiple in the pipeline. One-liners
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should save you the time you otherwise would spend coding a complex
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solution. There is little better than solving a challenging problem in a
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single line.
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## [References](#references)
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[[1] A Quarter Century of Unix, 1994, Peter Salus,
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ISBN:9780201547771](https://www.bookfinder.com/?isbn=9780201547771)
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[[2] The Art of UNIX Programming, 2003, Eric Raymond,
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ISBN:9780131429017](https://www.bookfinder.com/?isbn=9780131429017)
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