env: add set_preferred function

.config/shell/env

@@ -3,30 +3,37 @@
 # This file should be compatible with standard sh
 # shellcheck disable=SC2034
 
-# path_append from https://superuser.com/questions/39751/add-directory-to-path-if-its-not-already-there
 # checks if a path is already in the PATH and if it exists
 path_append() {
    if [ -d "$1" ]; then
-      # posix SH doesn't have [[, so we skip testing if the path is already in the PATH for simplicity
-      # shellcheck disable=SC3010
-      if command '[[' > /dev/null 2>&1 && [[ ":$PATH:" != *":$1:"* ]]; then
-         PATH="${PATH:+"$PATH:"}$1"
-      else
-         PATH="$PATH:$1"
-      fi
+      case ":$PATH:" in
+         (:"$1":) ;;
+         (*)
+            PATH="${PATH:+"$PATH:"}$1" ;;
+      esac
    fi
 }
 path_prepend() {
    if [ -d "$1" ]; then
-      # posix SH doesn't have [[, so we skip testing if the path is in the PATH already for simplicity
-      # shellcheck disable=SC3010
-      if command '[[' > /dev/null 2>&1 && [[ ":$PATH:" != *":$1:"* ]]; then
-         PATH="$1${PATH:+":$PATH"}"
-      else
-         PATH="$1:$PATH"
-      fi
+      case ":$PATH:" in
+         (:"$1":) ;;
+         (*)
+            PATH="$1${PATH:+":$PATH"}" ;;
+      esac
    fi
 }
+set_preferred() {
+   var="$1"
+   shift
+   for p; do
+      if command -v "$p" > /dev/null; then
+         eval "$var="'"$p"'
+         return
+      fi
+   done
+   echo "Error (env): couldn't find a valid candidate for \$$var"
+   unset var
+}
 
 # these would be temp vars, but ZSH does something weird where it makes them evaluate at runtime instead of
 export CONFIG_HOME="${XDG_DATA_HOME:-$HOME/.config}"
@@ -59,21 +66,21 @@ if [ "${EDITOR:-}" = "" ] ||
    [ "${EDITOR##*/}" = "nano" ] ||
    ! command -v "$EDITOR" > /dev/null
 then
-   if command -v nvim > /dev/null;then
-      export EDITOR=nvim
-   elif command -v vim > /dev/null;then
-      export EDITOR=vim
-   elif command -v vi > /dev/null;then
-      export EDITOR=vi
-   elif command -v nano > /dev/null; then
-      export EDITOR=nano
-   else
-      echo "Error: couldn't find a valid candidate for \$EDITOR" >&2
-   fi
+   set_preferred EDITOR nvim vim vi nano
 fi
 export SYSTEMD_EDITOR="$EDITOR"
 export VISUAL="$EDITOR"
 
+# Set a preferred terminal emulator
+if [ "${TERM_EMU:-}" = "" ]; then
+   set_preferred TERM_EMU kitty alacritty
+fi
+
+# Set a preferred terminal emulator
+if [ "${PAGER:-}" = "" ]; then
+   set_preferred PAGER less more
+fi
+
 # Tell zellij to auto attach by default instead of opening a new session
 export ZELLIJ_AUTO_ATTACH=true