this post was submitted on 15 Jan 2025
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    My heart goes out to shell programmers who have to support posix sh (lemmy.world)
    submitted 2 days ago by renzev@lemmy.world to c/linuxmemes@lemmy.world
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    Explanation for newbies:

    • Shell is the programming language that you use when you open a terminal on linux or mac os. Well, actually "shell" is a family of languages with many different implementations (bash, dash, ash, zsh, ksh, fish, ....)

    • Writing programs in shell (called "shell scripts") is a harrowing experience because the language is optimized for interactive use at a terminal, not writing extensive applications

    • The two lines in the meme change the shell's behavior to be slightly less headache-inducing for the programmer:

      • set -euo pipefail is the short form of the following three commands:
        • set -e: exit on the first command that fails, rather than plowing through ignoring all errors
        • set -u: treat references to undefined variables as errors
        • set -o pipefail: If a command piped into another command fails, treat that as an error
      • export LC_ALL=C tells other programs to not do weird things depending on locale. For example, it forces seq to output numbers with a period as the decimal separator, even on systems where coma is the default decimal separator (russian, dutch, etc.).

    • The title text references "posix", which is a document that standardizes, among other things, what features a shell must have. Posix does not require a shell to implement pipefail, so if you want your script to run on as many different platforms as possible, then you cannot use that feature.

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    [–] syklemil@discuss.tchncs.de 11 points 1 day ago (2 children) 
    #!/bin/bash
set -euo pipefail

if [[ -z "${1:-}" ]]
then
  echo "we need an argument!" >&2
  exit 1
fi
    [–] rumba@lemmy.zip 3 points 1 day ago (1 children)

    God I love bash. There's always something to learn.

    my logical steps

    • #! yup
    • if sure!
    • [[ -z makes sense
    • ${1:-} WHAT IN SATANS UNDERPANTS.... parameter expansion I think... reads docs ... default value! shit that's nice.

    it's like buying a really simple generic car then getting excited because it actually has a spare and cupholders.

    [–] syklemil@discuss.tchncs.de 3 points 12 hours ago

    Yeah, there's also a subtle difference between ${1:-} and ${1-}: The first substitutes if 1 is unset or ""; the second only if 1 is unset. So possibly ${foo-} is actually the better to use for a lot of stuff, if the empty string is a valid value. There's a lot to bash parameter expansion, and it's all punctuation, which ups the line noise-iness of your scripts.

    I don't find it particularly legible or memorable; plus I'm generally not a fan of the variable amount of numbered arguments rather than being able to specify argument numbers and names like we are in practically every other programming language still in common use.

    [–] tetris11@lemmy.ml 3 points 1 day ago* (last edited 1 day ago) (1 children)

    That's good, but if you like to name your arguments first before testing them, then it falls apart

    #!/bin/bash
set -euo pipefail

myarg=$1

if [[ -z "${myarg}" ]]
then
  echo "we need an argument!" >&2
  exit 1
fi

    This fails. The solution is to do myarg=${1:-} and then test

    Edit: Oh, I just saw you did that initialisation in the if statement. Take your trophy and leave.

    [–] syklemil@discuss.tchncs.de 2 points 1 day ago* (last edited 1 day ago) (1 children)

    Yeah, another way to do it is

    #!/bin/bash
set -euo pipefail

if [[ $# -lt 1 ]]
then
  echo "Usage: $0 argument1" >&2
  exit 1
fi

    i.e. just count arguments. Related, fish has kind of the orthogonal situation here, where you can name arguments in a better way, but there's no set -u

    function foo --argument-names bar
  ...
end

    in the end my conclusion is that argument handling in shells is generally bad. Add in historic workarounds like if [ "x" = "x$1" ] and it's clear shells have always been Shortcut City

    Side note: One point I have to award to Perl for using eq/lt/gt/etc for string comparisons and ==/</> for numeric comparisons. In shells it's reversed for some reason? The absolute state of things when I can point to Perl as an example of something that did it better

    [–] tetris11@lemmy.ml 2 points 1 day ago (1 children)

    Perl is the original GOAT! It took a look at shell, realised it could do (slightly) better, and forged its own hacky path!

    [–] dx1@lemmy.world 2 points 1 day ago* (last edited 1 day ago)

    I was about to say, half the things people write complex shell scripts for, I'll just do in something like Perl, Ruby, Python, even node/TS, because they have actual type systems and readability. And library support. Always situation-dependent though.