Which command substitution do you prefer in shell scripts: backquotes `` or $() syntax?

a year ago by kiri to c/linux

Looks like $(...) is better, but I still pretty often see `...` in some articles.

IanTwenty 18 points a year ago

$() for me, to quote from

https://www.shellcheck.net/wiki/SC2006

Backtick command substitution `...` is legacy syntax with several issues.

It has a series of undefined behaviors related to quoting in POSIX.

It imposes a custom escaping mode with surprising results.

It's exceptionally hard to nest.

$(...) command substitution has none of these problems, and is therefore strongly encouraged.

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confusedpuppy 4 points a year ago

Shellcheck is a great tool for scripting.

When I'm building a new script, I usually add the following function to the script and run the function before anything else. The script will exit immediately if any issues are found so I have a chance to correct things. If no issues are found, the script will simply continue.

It's small and simple so it's easy to remove when I'm done building a script.

script_check() {
    if ! shellcheck "${0}"; then
        exit 1
    fi
}

script_check

Shellcheck has helped me learn a lot about scripting and I strongly recommend using it too.

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IanTwenty 5 points a year ago

That's good. There are also editors that can run it for you and highlight the issues whilst you type, neovim being one.

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nous 3 points a year ago

Why wrap it in a function at all? Why not just put the if at the top of the file?

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HelloRoot 18 points a year ago

never backquotes, it's unintuitive

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30p87 10 points a year ago

$()

Backticks are pretty old syntax.

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MonkderVierte 1 point a year ago

Deprecated btw.

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red_bull_of_juarez 7 points a year ago

I'm using fish, so it's ().

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trevor 2 points a year ago

I prefer this as well, but just adding that Fish also supports $() for those that don't know.

I keep hearing people that haven't used modern versions of Fish say that it's somewhat different from Bash and strays from POSIX compatibility quite a bit. While the latter is true, Fish has added many bash-isms over the years, so most scripting idioms you're familiar with will work there too.

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excess0680 3 points a year ago

By some sheer coincidence, I searched this topic today. I’ve been a consistent user of the parenthesis expansion, but never thought of why I preferred one or the other.

I suppose the primary advantage is that $() will expand in a consistent way. You can even nest quotes and more expansions in one, while you’d struggle the same with backtick notation.

So I’ll just keep using parentheses.

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Moss_the_TeXie 1 point a year ago

@kiri
$()
Better reachable on german keyboard. Also muscle memory … YmmMV. ;-)

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aubeynarf -1 points a year ago

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