Improve interactiveness checks (#3449)

* [bash] return instead of not executing an if-block, when non-interactive

This should keep the code more readable, be less error prone (accidentally doing
something outside the if-block and aligns the code with what’s already done for
zsh.

`0` is returned, because it shall not be considered an error when the script is
(accidentally) sourced from a non-interactive shell.

If executed as a script (rather than sourced), the results are not specified by
POSIX but depend on the shell, with bash giving an error in that case.

Signed-off-by: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>

* [shell] exit immediately when called from non-interactive shell

The shell execution environment shouldn’t be modified at all, when called from a
non-interactive shell.

It shall be noted that the current check may become error prone for bash, namely
in case there should ever be a differentiation between `i` and `I` in the
special variable `-` and bash’s `nocasematch`-shell-option be used.

Signed-off-by: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>

shell/key-bindings.bash

@@ -11,6 +11,9 @@
 # - $FZF_ALT_C_COMMAND
 # - $FZF_ALT_C_OPTS
 
+[[ $- =~ i ]] || return 0
+
+
 # Key bindings
 # ------------
 __fzf_select__() {
@@ -27,8 +30,6 @@ __fzf_select__() {
     done
 }
 
-if [[ $- =~ i ]]; then
-
 __fzfcmd() {
   [[ -n "${TMUX_PANE-}" ]] && { [[ "${FZF_TMUX:-0}" != 0 ]] || [[ -n "${FZF_TMUX_OPTS-}" ]]; } &&
     echo "fzf-tmux ${FZF_TMUX_OPTS:--d${FZF_TMUX_HEIGHT:-40%}} -- " || echo "fzf"
@@ -130,5 +131,3 @@ fi
 bind -m emacs-standard '"\ec": " \C-b\C-k \C-u`__fzf_cd__`\e\C-e\er\C-m\C-y\C-h\e \C-y\ey\C-x\C-x\C-d"'
 bind -m vi-command '"\ec": "\C-z\ec\C-z"'
 bind -m vi-insert '"\ec": "\C-z\ec\C-z"'
-
-fi