How to check if the is fish?

[maandree]

Is it possbile for a shell script to determine if the executing shell is the fish shell?

[terlar]

Maybe this could work:

➤ basename $SHELL
fish

[maandree]

basename?

$SHELL is not set by fish.
I do known when $SHELL is set, but on by user it is always /bin/bash which is my default shell.

[terlar]

Ah, I see. Nevermind then, will think about it.

[zanchey]

You could check for the existence of variables like __fish_bin_dir, but realistically the shell you are executing is fish if you can parse fish syntax. What are you trying to achieve?

[maandree]

In case a script is not runnable in fish, I want to suggest other shells to execute with that does work, indeed of have a lot of error messages printed out, alternatively use fish version of the script.

In case the user use fish as his shell, but /bin/sh links to /bin/bash, bash will be the executing shell but fish's variables will still exist, so checking for variables is not safe.

The only safe possibility I can think of is if there is a built in function that will print fish.

[stestagg]

Running a correctly written bash script from fish shouldn't break things. Could you provide a more concrete example?

It may help with understanding what type of detection you need, too.

[maandree]

shells have different syntax compatibility, for example, bash extends posix;
so it is usable for all shells to implement.

The instruction
(hash chmod 2>/dev/null) || (br=1 ; ro=1 ; echo 'Missing chmod, install coreutils [build+runtime required]'
gives 3 error messages in fish.

[stestagg]

That makes sense, but I'm not sure I understand why you'd want to run a bash command in a fish environment?

if this is in a script, then wouldn't adding #!/bin/bash at the top work?

[maandree]

It works on all shells that I have have tested except fish, is I think using #!/bin/sh is preferable.

[ridiculousfish]

The answer at http://stackoverflow.com/questions/3199893/howto-detect-bash-from-shell-script suggests that $BASH_VERSION is an unexported variable, and that zsh follows suit with $ZSH_VERSION.

fish and tcsh both have the version variable; neither of them is exported.

It seems like adding an unexported $FISH_VERSION would be helpful.

[zanchey]

Seems like a good idea.

(Note that setting /bin/sh to a non-POSIX-sh-compatible shell is a terrible idea, though, and large parts of your system will probably stop working.)

[maandree]

Naturally that [setting /bin/sh] is a bad idea.
Roughly how compatible is fish with POSIX?

[ridiculousfish]

fish's built-ins are generally compliant (e.g. test) but fish itself is not POSIX compliant because it has its own syntax for things like variables. A shell script that does anything more than just run commands will not run successfully in fish.

[zanchey]

zanchey@259c6fc

[maandree]

That should do the trick.