Define function in fish, use it with watch

Question

I want to define a function, and call that function every n seconds. As an example:

function h
    echo hello
end

Calling h works:

david@f5 ~> h
hello

But when using watch, it doesn't...

watch -n 60 "h"

...and I get:

Every 60.0s: h                                      f5: Wed Oct 10 21:04:15 2018

sh: 1: h: not found

How can I run watch in fish, with the function I've just defined?

Answer 1

Another way would be to save the function, then ask watch to invoke fish:

bash$ fish
fish$ function h
    echo hello
end
fish$ funcsave h
fish-or-bash$ watch -n 60 "fish -c h"

funcsave saves the named function definition into a file in the path ~/.config/fish/functions/, so ~/.config/fish/function/h.fish in the above case.

Answer 2

There is no easy way. By default watch uses /bin/sh to run commands but takes -x:

   -x, --exec
          Pass  command  to  exec(2)  instead  of  sh -c which reduces           
          the need to use extra quoting to get the desired effect.

However, nothing will not work with fish because h function is not exported to environment:

$ watch -n 5 --exec  fish -c h
Every 5.0s: fish -c h                                                                                                                                                                 comp: Wed Oct 10 21:30:14 2018

fish: Unknown command 'h'
fish:
h
^

In bash you could export a function to environment with export -f and use it inside watch like this:

$ h1 () {
> echo hi
> }
$ type h1
h1 is a function
h1 ()
{
    echo hi
}
$ export -f h1
$ watch -n 60 bash -c h1
Every 60.0s: bash -c h1                                                                                                                                                               comp: Wed Oct 10 21:29:22 2018

hi

If you use fish you can create a wrapper script and call it with watch:

$ cat stuff.sh
#!/usr/bin/env fish

function h
    date
end

h

$ watch -n5 ./stuff.sh

Also note that fish has . and source so you can define function in another file and be able to re-use it in other scripts like that:

$ cat function
function h
    echo hi
end
$ cat call.sh
#!/usr/bin/env fish

. function

h
$ watch ./call.sh

Answer 3

Yes, I did it! It does the job, but I still wish fish had something native. I choose the name blotch so it doesn't interfere with bash's watch.

function blotch
    # 2018-10-10
    # 
    # This is like the watch command of bash,
    # but re-implemented in fish.
    # 
    # It takes two arguments:
    #   n: the interval in seconds
    #   fun: a fish function
    # 
    # Therefore, it is always used as:
    # 
    #   blotch n fun
    # 
    # Take note that you should start fish with
    # 
    #   sudo fish
    #   
    # before doing anything with blotch that
    # requires administrator privileges.

    set time (string split " " -- $argv)[1]
    set command (string split " " -- $argv)[2]
    while true
        sleep $time
        eval $command
    end
end

And save the function for later use.

funcsave blotch

Answer 4

Another quite easy way would be...

function fonzie
    echo "This is Fonzie!"
end

while true
    fonzie
    sleep 10
end