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Comment by shmerl | Hacker News Reader

> And now for the final lolz. I’ve said above that these are the commands you use to evaluate expressions… but the shell also has expressions of its own via the !, &&, and || operators—all of which work on command exit statuses.

It works for simulating very basic boolean expressions, but it gets ugly quickly if you need some more complex combos of NOT, OR and AND. I wish Bash had proper boolean expressions support.

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It works fine, you can satisfy your boolean logic needs with bash tests and exit codes.

You'd be amazed at how much of the world runs (just fine!) on bash conditionals.

You'd be surprised how much of the world runs on cobol and Fortran.

Doesn't mean those are good or even okay or that people should choose to use them.

Modern post-2012 Fortran is excellent, and the compiler produces very fast code, GPU or otherwise. And it is very portable.

What do you mean? Bash does have (), {}, !, &&, ||

What else do you need for "proper Boolean expressions support"?

I don't think you can assign boolean variables to boolean expressions, becasue there is no boolean type.

Something like this won't work to become false:

    foo=true
    bar=false

    baz=$foo && $bar
    echo $baz

Or even simply:

    foo=! $foo

With numeric expressions, you can at least use $((...))

Yeh you'd have to do something like

    foo=true
    bar=false

    $($foo) && $($bar); baz=$?
    case $baz in
    1) echo false;;
    0) echo true;;
    esac

It just ain't worth it.

Yeah, that's very convoluted. It would be useful to have some context for boolean expressions, similarly how $((...)) works for numeric ones.

But you can do

    foo=0 # true
    bar=1 # false

    [ $foo = 0 ] && [ $bar = 0 ]
    baz=$?
    echo $baz

The syntax is a bit unusual coming from more modern languages, as is the use of 0 as true. But you can express whatever conditionals you want. Remember that C originally had no dedicated boolean type either.

You could also use numerical expressions although I don't recommend it due to being even less readable (even more so if you have expression complex enough that you need to protect against overflow):

    baz=$((foo + bar)) // foo && bar
    baz=$((foo * bar)) // foo || bar

That still doesn't make it look nice, since if you use false / true, you can use variables directly in if checks. For example:

    foo=true

    if $foo; then
      echo yes
    fi

But with 0 / 1 - that won't work. I.e. you can get some, but not all features of a normal boolean type in various ways.

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