Fish equivalent of bash $(command) notation

Question

I am currently trying out the fish shell instead of using bash. One type of notation I'm having trouble learning the fish-equivalent notation for is $(command), similar to how it is described in this SOF post. How do I write this using fish? Keep in mind that I could use backslash characters around the command I want to evaluate, but the linked post and other posts discourage this because it is an old style of evaluating commands.

Specifically, this is the bash command I want to convert to fish syntax (for initializing rbenv during startup of the shell):

eval "$(rbenv init -)"

• iscfrc: Per this entry in the fish FAQ, sub-commands are denoted by surrounding them with parenthesis. e.g., set foo (echo bar); echo $foo outputs bar.

Answer 1

In fish, $ is used only for variables. Correct notation equivalent to bash $(command) is just (command) in fish.

• Leo Cavalcante: eval (docker-machine env default --no-proxy --shell=fish) :D thanks for the help too

Answer 2

FYI: If you additionally need to use this inside a string:

echo "Found "(count $PATH)" paths in PATH env var"

• aasutossh: So there is no way around temporarily closing the quote and reopening right after. fishshell.com/docs/current/tutorial.html#command-substitutions

Answer 3

Since fish 3.4 (released March 2022), $()-substitution is supported. It works the same as ()-substitution, but can be used inside double-quoted strings.

• Pranav: I want to use ``` alias math=math ()" ``` so that I can use brackets in the calculation by default. Is this doable?
• ash: @Pranav please ask a new question for the best chance of someone writing an answer :)

Answer 4

Watch out that () and $() in fish are not totally equivalent to $() in bash.

Fish only splits command substitutions on newlines.

• In fish cmd $(echo "A B C") is equivalent to cmd 'A B C', but
• in bash cmd $(echo "A B C") is equivalent to cmd A B C.

But cmd $(echo -e "A\nB\nC") is indeed equivalent in fish and bash.