echo 'I wrote a Bash book' >> /dev/world

https://paperless.blog/newline-guide-to-bash-scripting

by l0b0 • 5 years ago

60 30 5 years ago

l0b010• 5 years ago

This one hopefully has a bit of an original twist by being focused on maintainability and understanding some of why Bash is different from most programming languages, and by being aimed at software developers mainly working in other languages.

I'd like to write a follow-up article about the process of getting there if there's any interest. AMA.

hackthefender• 5 years ago

It is not even theoretically possible to write a piece of software which will behave the same no matter how and where it is run.

Can you elaborate on that? I'm sure it's both true and false depending on your definition of "how and where it is run," but wondering what you had in mind specifically.

hdjjhhvvhga• 5 years ago

As for the "theoretically" part, it is enough to prove that at least one such a system exists that will yield another result than expected. There could be various reasons, from human/software errors to hardware errors like memory bit flips. Since we know these do exist, it is not even theoretically possible to write a piece of software which will behave the same no matter how and where it is run, although it is certainly possible to write it in such a way that it will behave the same in a vast majority of cases.

chubot2• 5 years ago

I'd say that containers are actually something that makes Unix shell a lot more valuable and predictable, and one reason that I'm working on https://www.oilshell.org/ .

A container is basically a "virtualenv" for shell, and it's honestly better than that because:

- it's more general (it isolates every language, not just Python), and

- not even bigger (e.g. an Alpine Linux container is not that much bigger than the Python install in every virtualenv!)

Traditionally you do indeed have the problem that copying a shell script from one machine to another basically guarantees you nothing about how it will work. These days we deploy containers, which solve the problem, and that's why shell is used so much in the cloud (e.g. anything with Github Actions has a boatload of shell)

Even more on that: https://www.oilshell.org/blog/2021/07/cloud-review.html

l0b010• 5 years ago

I remember reading (sorry, can't remember the source) that it's been proven mathematically that there's no way to write code which will run the same on any Turing-equivalent processor. Obviously that's not saying much since Bash is pretty far abstracted from the CPU, it's more of a caveat that I've hardly ever seen a discussion about Bash which doesn't involve at least one "well, actually" comment about how the suggested code doesn't do what the autor purports on some incredibly niche platform or with some highly unusual configuration.

Hitton• 5 years ago

Author didn't write a book, he made a course.

szszrk2• 5 years ago

Judging by the index it is more like a "shell 101" plus some bash. Also a paid one.

It's cool, people need such stuff but the title is misleading and the article is basically an ad for a paid service.

l0b010• 5 years ago

Thank you for the feedback! It's not a beginner's guide; it really is intended for people with at least a reasonable understanding of programming concepts such as scope and the difference between imperative and other types of programming.

l0b010• 5 years ago

It was originally a book, however the publisher reformatted it to a book just before release, possibly because of the length.

Y_Y• 5 years ago

Please refrain from appending to /dev/world as it is already a huge mess.

choeger• 5 years ago

Imagine they'd used '>' instead. I don't think that I would appreciate a hard reset of that particular block device.

l0b010• 5 years ago

Don't worry, I always `set -o noclobber`!

l0b010• 5 years ago

You're right, I should probably have used `patch` instead.

hulitu• 5 years ago

they shall symlink /dev/world to /dev/null

ape42• 5 years ago

Slightly off topic, is there a nice/modern way to deal with filenames that can have spaces in bash scripts? The only solutions I have seen use tons of quotes are are unreadable/unmaintainable.

chubot2• 5 years ago

You can set IFS='' globally, which disables splitting. (And you have to make sure it stays that way, since there are some idioms which modify IFS)

Although there is the "empty elision" case related to splitting: if x='', then $x is different than "$x", even if IFS=''.

You could also use zsh which doesn't do word splitting, but does "empty elision". (I'd say zsh is a better interactive shell than a scripting language, but I've seen it used on occasion.)

Or you can use OSH, which will run your bash script as is. And then you can opt into shopt -s simple_word_eval or the group shopt -s oil:basic, and EVERYTHING will be "unmolested", quotes or not:

http://www.oilshell.org/blog/2021/04/simple-word-eval.html

OskarS• 5 years ago

Just be careful to quote filename variables. Don't write this:

    cp $FILENAME $TARGET

Write this:

    cp "$FILENAME" "$TARGET"

It's a bit annoying, but it's not that bad, and certainly not unmaintainable.

ebeip902• 5 years ago

This is the correct answer!

ape42• 5 years ago

There are tons of other cases, eg:

    find . -name "*.csv" -print | while IFS= read -r file; do
    done

ilyash• 5 years ago

... and hope that $FILENAME does not start with a dash... just in case you don't have enough landmines to step on.

enriquto• 5 years ago

the true (and unpopular) solution is to disallow spaces in filenames

pama• 5 years ago

I strongly recommend the book Unix Power Tools for all such questions. Quotes become easier to grok once you think of different ways to remove meaning of special characters. Basically, 1) backslash removes special meaning of the next character, 2) surrounding by double quote removes special meaning of all characters except backslash, dollar, and backtick, and 3) surrounding by single quotes removes all special meanings.

ebeip902• 5 years ago

Coffee is for closers^W quoters. ABQ.

Always. Be. Quoting.

Also, you should be checking your Bash scripts with shellcheck, which will tell you when to do this with ~99% accuracy.

(For the uninitiated: https://www.youtube.com/watch?v=GrhSLf0I-HM)

l0b010• 5 years ago

I'm afraid quotes are the way to go. The alternatives are basically escaping (which looks even worse) or using a different language. The book also mentions a few more tricks you probably want to know about for dealing with the really tricky stuff, like filenames starting with a hyphen or ending with a newline.

sramsay• 5 years ago

I'm a huge fan of Bash, and am always interested in upping my skills. My only question is this: Is it better than the (free) Bash Guide?

https://mywiki.wooledge.org/FullBashGuide

Because that is a pretty amazing resource.

l0b010• 5 years ago

I agree, Greg's Wiki has a lot of amazing content. Certainly there will be a bit of overlap, but the focus of the book is a bit different:

- It is more relevant for scripting than the interactive command line. For example, it includes

- I've taken a lot of care to write non-trivial example code, which is useful to show when and where constructs are useful, and which other constructs they are usually used with. For example, the argument parsing part shows not just how to use `getopt`, but also how it's meant to be used with `eval`, `unset`, `while`, `case`, and `shift`; the standard `--` option/argument separator; how to handle unimplemented options (anything mentioned by `getopt` but not matched by any `case` statements); and how to deal with the remaining arguments.

- The non-trivial code has been linted using `shellcheck` and a lot of it is tested with `shunit2` (533 lines of tests in total, which are included as a download).

LambdaComplex• 5 years ago

I'm at the level where any Bash book/guide/etc that wants my attention needs to prove that it's more useful than Greg's Wiki.

Chances are, it isn't.

https://mywiki.wooledge.org/BashGuide

https://mywiki.wooledge.org/BashFAQ

https://mywiki.wooledge.org/BashPitfalls

l0b010• 5 years ago

Certainly there's a lot of stuff in common. I read every single article on Greg's Wiki a couple years before starting this book, and it's informed a lot of my opinions and understanding of the fundamentals of Bash. I do disagree with what seems to be the prevailing wisdom on Greg's Wiki on some points though. For example, I strongly support using errexit rather than trying to implement all the error handling yourself.

echo 'I wrote a Bash book' &gt;&gt; /dev/world

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echo 'I wrote a Bash book' >> /dev/world