What's the equivalent to ${var:-defaultvalue} in fish?

Question

Hello I am trying to translate my .bashrc to fish format almost done, mostly is clear on the documentation but this part is giving me a headache.. is so my gnupg works with

Answer 1

You should not change your login shell until you have a much better understanding of fish syntax and behavior. For example, in fish the equivalent of $$ is %self or $fish_pid depending on which fish version you are using. You should always specify the version of the program you are having problems with.

Assuming you're using fish 2.x that would be written as

if not set -q gnupg_SSH_AUTH_SOCK_by
or test $gnupg_SSH_AUTH_SOCK_by -ne %self
    set -gx SSH_AUTH_SOCK "/run/user/$UID/gnupg/S.gpg-agent.ssh"
end

Also, notice that there is no equal-sign between the var name and value in the set -x.

Answer 2

Since ${var:-value} expands to value if $var is empty, you can always replace it by writing your code out the long way:

begin
  if test -n "$gnupg_SSH_AUTH_SOCK_by"
    set result "$gnupg_SSH_AUTH_SOCK_by"
  else
    set result 0
  end

  if [ "$result" -ne %self ]
    set -x SSH_AUTH_SOCK "/run/user/$UID/gnupg/S.gpg-agent.ssh"
  end
  set -e result
end

_{Note that I don't use (a) endorse, (b) condone the use of, or (c) fail to hold unwarranted prejudices against users of, fish. Thus, my advice is very much suspect, and it's likely that there are considerably better ways to do this.}

Answer 3

I had a similar question, related to XDG_* variables.

var1="${XDG_CACHE_HOME:-$HOME/.cache}"/foo
var2="${XDG_CONFIG_HOME:-$HOME/.config}"/foo
var3="${XDG_DATA_HOME:-$HOME/.local/share}"/foo
some-command "$var1" "$var2" ...

What I found as the best alternative is to simply set univeral variables once for the defaults--

set -U XDG_CACHE_HOME ~/.cache
set -U XDG_CONFIG_HOME ~/.config
set -U XDG_DATA_HOME ~/.local/share

Then in fish config file(s) or scripts, simply use "$XDG_CONFIG_HOME"/.... The value of an exported environment variable will override the universal variable if set, otherwise the universal variable is there as a default/fallback. If the universal variable is used, it is not exported to child processes, while an exported environment variable is, which provides the full equivalent to bash|zsh parameter expansion.