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@zephyr@lemmy.world to Programming@programming.dev • 2 years ago

How do you shell expand your variables and why?

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How do you shell expand your variables and why?

lemmy.world

@zephyr@lemmy.world to Programming@programming.dev • 2 years ago
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  • thingsiplay
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    60•2 years ago

    @zephyr echo "${HOME}/docs"

    • @bloopernova@programming.dev
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      13•
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      2 years ago

      This is the best way. It’s also the way the Shellcheck wants sometimes recommends.

      • thingsiplay
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        8•2 years ago

        @bloopernova As you mention it, here the links for anyone interested: Online tool https://www.shellcheck.net/ and you can install it locally too https://github.com/koalaman/shellcheck .

        • @hascat@programming.dev
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          4•2 years ago

          While this looks like a handy tool, it does make me think shell scripting itself needs a cleaner approach than what we have currently.

          • thingsiplay
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            1•2 years ago

            deleted by creator

      • Gamma
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        2 years ago

        This isn’t true. Shellcheck doesn’t insist on braces unless it thinks you need them.

        • @bloopernova@programming.dev
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          3•2 years ago

          Oh! I didn’t know that (um, obviously lol)

          I’ll edit my comment.

    • Drew Belloc
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      5•2 years ago

      This is the way

    • @Simulation6@sopuli.xyz
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      4•2 years ago

      I also do this so the variables are more easily spotted.

    • @brennesel@feddit.de
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      3•2 years ago

      This is the right way

    • Gamma
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      3•2 years ago

      This has never stuck with me, and I hadn’t thought about why until now. I have two reasons why I will always write ${x}_$y.z instead of ${x}_${y}.z:

      • Syntax highlighting and shellcheck have always caught the cases I need to add braces to prevent $x_ being expanded as ${x_}.
      • I write a lot of Zsh. In Zsh, braces are optional in way more cases. "$#array[3]" actually prints the length of the third item in array, rather than (Bash:) the number of positional parameters, then the string 'array[3]'.
      • thingsiplay
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        3•2 years ago

        @gamma I just use them out of consistency and principle, so I don’t need to think in which case it is required or not.

      • Cyclohexane
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        1•2 years ago

        I will always write ${x}_$y.z instead of ${x}_${y}.z:

        The difference between the two seems different to what’s in the OP. Is there a typo here?

        • Gamma
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          1•2 years ago

          in the OP

          My reply is to a commenter who said they prefer "${HOME}/docs" over both options in the original image ("$HOME/docs" or "$HOME"/docs). Many people prefer to always include braces around the parameter name out of consistency, instead of only when they are required.

          My comment explained why my habit is to only include braces when they are necessary.

  • @ilega_dh@feddit.nl
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    38•2 years ago

    find “$(echo $HOME > variable_holder.txt && cat variable_holder.txt)/$(cat alphabet.txt | grep “d”) $(cat alphabet.txt | grep “o”)$(cat alphabet.txt | grep “c”)$(cat alphabet.txt | grep “s”)”

    This is the easiest method

    • Eager Eagle
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      7•2 years ago

      when you’re paid by character written

    • igorlogius
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      7•2 years ago

      no eval ?

    • @ale@lemmy.world
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      5•2 years ago

      This really enterprises my bash.

    • thingsiplay
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      3•
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      2 years ago

      @ilega_dh You don’t need cat in cases when grep "d" alphabet.txt can read from file too. Edit: But obviously your comment was more of a joke to over complicate it. So never mind then.

      • gendulf
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        3•2 years ago

        To be safe, should probably output grep to a file, then cat that.

        • @ilega_dh@feddit.nl
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          2•2 years ago

          Agreed. Everything in Linux is a file so let’s keep it that way.

          • @ImpossibleRubiksCube@programming.dev
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            2 years ago

            deleted by creator

    • monsterpiece42
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      1•2 years ago

      What should I search to better understand what is written here? Don’t mind learning myself, just looking for the correct keywords. Thanks!

      • @oneiros@lemmy.blahaj.zone
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        2•2 years ago

        This comment is a joke and you wouldn’t want to do it like that in reality, but here are some related keywords you could look up: “Unix cat”, “Unix pipeline”, “grep”, “output redirection”, “command substitution”.

        • monsterpiece42
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          1•2 years ago

          Perfect, I have some light reading for the evening!

      • @marcos@lemmy.world
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        2•2 years ago

        Read the Bash manual. That one patter on the GP is called “Command Substitution”, you can search for it.

        • monsterpiece42
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          1•2 years ago

          Thanks!

      • @priapus@sh.itjust.works
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        1•2 years ago

        ExplainShell should help

  • key
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    17•2 years ago

    First one, then the other, then I forget the quotes, then I put them in single quotes by accident, then I utilize that “default value” colon syntax in case I’m missing HOME , then I just stick to ~ for the rest of the file.

  • Gamma
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    2 years ago

    Typically find "$HOME/docs", but with a few caveats:

    • In Zsh or Fish, the quotes are unnecessary: find $HOME/docs

    • If I’m using anything potentially destructive: mv "${HOME:?}/bin" ...

    • Of course, if it’s followed by a valid identifier character, I’ll add braces: "${basename}_$num.txt"

  • @karlhungus@lemmy.ca
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    5•2 years ago

    I do what the linter tells me to: https://github.com/koalaman/shellcheck

  • @ImpossibleRubiksCube@programming.dev
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    2 years ago

    deleted by creator

  • thingsiplay
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    1•2 years ago

    deleted by creator

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