Builtin Commands

  [I/O]           read        echo       printf
                  readarray   mapfile
  [Run Code]      source .    cmd/eval   trap
  [Set Options]   set         shopt
  [Working Dir]   cd          chdir      pwd       
                  pushd       popd       dirs
  [Completion]    complete    compgen    compopt   compadjust   compexport
  [Shell Process] exec      X logout 
                  umask       ulimit     times
  [Child Process] jobs        wait
                  fg        X bg       X kill        X disown 
  [External]      test [      getopts
  [Conditional]   cmd/true    cmd/false                colon :
  [Introspection] help        hash       cmd/type    X caller
  [Word Lookup]   command     builtin
  [Interactive]   alias       unalias    history       fc     X bind
X [Unsupported]   enable
