Stop fish complaining: fish: $? is not the exit status. In fish, please use $status

Question

I am building a script that should work in csh, bash, and fish with no change:

This does the right thing in all the shells,

perl -e '$bash=shift;$csh=shift;for(@ARGV){unlink;rmdir;}if($bash=~s/h//){exit$bash;}exit$csh;' "$?h" "$status" $PARALLEL_TMP
                                                                                      

except that fish complains:

fish: $? is not the exit status. In fish, please use $status.

Is there a compatible way I can tell fish: Please do not warn, I know what I am doing.

Answer 1

$ bash -c 'false; echo "[$status]" "[`echo \$?h`]"'
[] [1h]
$ csh -c 'false; echo "[$status]" "[`echo \$?h`]"'
[1] [0]
$ fish -c 'false; echo "[$status]" "[`echo \$?h`]"'
[1] [`echo $?h`]

Uses the fact that ` is not special in fish, and that Bourne-like shells do an extra level of backslash processing within `...`.

You should also be able to use eval, supported by all three shells, and have different code ready for all three in some environment variable, which would simplify things.

if ($csh || $fish) {
   ENV{CHECK_STATUS} = q{perl -e '...' $status};
} else {
   ENV{CHECK_STATUS} = q{perl -e '...' "$?"};
}
exec $shell, "-c", ...;

and the shell code would be eval "$CHECK_STATUS" (beware that for csh, $CHECK_STATUS must not contain newline characters).

Answer 2

Is there a compatible way I can tell fish: Please do not warn, I know what I am doing.

There is not. Cross-compatible scripts between fish and other shells are not a thing, because fish is not compatible.

In most cases what you want to do is to pick a shell and write a script for it, with a shebang and everything, the most widely available choice being "/bin/sh".

Then fish can just run your script like it can run a script written in python or ruby, or programs written in C.

In some cases you do need the shell to source your script because you want it to effect environment changes in your shell. In that case the simplest way to allow that would be to have the script print

export var=val

lines and have fish source it via /path/to/script | source (and other shells similarly).