Simplify command validation and help

src/libexec/saturnin-iam

 # self help
 #
 
-available_commands() {
-    echo afk
-    echo at
-    echo back
-    echo gone
-    echo ooo
-    echo wfh
-    echo undocking
-    echo zleeping
-}
+available_commands="afk at back gone ooo wfh undocking zleeping"
 
 usage() {
-    cmd_hint=$(
-        available_commands \
-            | head -c -1 \
-            | tr '\n' '|'
-    )
-    mkusage "$cmd_hint"
+    mkusage $available_commands
 }
 
 
 
 test -n "$cmd" || usage
 
-available_commands | grep -qse ^$1 || usage
+echo $available_commands | grep -qw "$cmd" || usage
 
 shift