how to debug fish script?

Question

You can debug a bash script like this:

bash -x script [arg1 ...]`

Question

What is the fish equivalent?

Answer 1

Fish use a similar flag system:

fish -d 3 script.fish

Where d is the debug flag followed by the verbosity level:

-d or --debug-level=DEBUG_LEVEL specify the verbosity level of fish. A higher number means higher verbosity. The default level is 1.

Answer 2

Since https://github.com/fish-shell/fish-shell/issues/3427 was merged there is now

fish_trace=on script.fish

fish_trace is just a variable, so you can set it globally or scope it locally inside functions and scripts

function im-still-debugging
   set -l fish_trace on
   ... etc
end

and turn it off with

set --erase fish_trace

as of fish 3.2, fish ignores the actual value you set, it only cares that it is set.