feat: unset all enviroment variables ASDF_{PLUGIN}_VERSION

lib/commands/command-export-shell-version.bash

@@ -2,20 +2,49 @@
 # shellcheck source=lib/functions/versions.bash
 . "$(dirname "$(dirname "$0")")/lib/functions/versions.bash"
 
+unset_all_fish() {
+  printf "for var in (env | awk -F= '/^ASDF_[A-Za-z0-9_]+_VERSION=/ {print \$1}')\n"
+  printf "    echo Removing Env: \$var\n"
+  printf "    set -e \$var\n"
+  printf "end\n"
+}
+unset_all() {
+  printf "for var in \$(env | awk -F= '/^ASDF_[A-Za-z0-9_]+_VERSION=/ {print \$1}'); do\n"
+  printf "    echo Removing Env: "
+  printf "    \$var\n"
+  printf "    unset -v \$var\n"
+  printf "done\n"
+}
+
 # Output from this command must be executable shell code
 shell_command() {
   local asdf_shell="$1"
   shift
 
+  if [ "$1" = '--unset-all' ]; then
+    case "$asdf_shell" in
+    fish)
+      unset_all_fish
+      ;;
+    elvish)
+      # TODO
+      printf "asdf: Flag '--unset-all' not implemented for Elvish shell" >&2
+      ;;
+    *)
+      unset_all
+      ;;
+    esac
+    exit 0
+  fi
+
   if [ "$#" -lt "2" ]; then
-    printf "Usage: asdf shell <name> {<version>|--unset}\n" >&2
+    printf "Usage: asdf shell {<name> {<version>|--unset}|--unset-all}\n" >&2
     printf "false\n"
     exit 1
   fi
 
   local plugin=$1
   local version=$2
-
   local upcase_name
   upcase_name=$(tr '[:lower:]-' '[:upper:]_' <<<"$plugin")
   local version_env_var="ASDF_${upcase_name}_VERSION"