Cross Reference: /ast/src/cmd/coshell/title

# add to (+), delete from (-), set [=], or print (.) window title
# arguments are eval'd before printing
# title text string exported in TITLE_TEXT

function title # [ + | - | = | . ] title ...
{
    typeset x t="$TITLE_TEXT"

    case $1 in
    +)  shift
        case $# in
        0)  ;;
        *)  for x
            do  case " $t " in
                *" $x "*)   ;;
                "  ")       t=$x ;;
                *)      t="$t $x" ;;
                esac
            done
            case $t in
            $TITLE_TEXT)    return 1 ;;
            esac
            ;;
        esac
        ;;
    -)  shift
        case $# in
        0)  ;;
        *)  for x
            do  case " $t " in
                *" $x "*)   t="${t%?( )$x*}${t##*$x?( )}" ;;
                esac
            done
            case $t in
            $TITLE_TEXT)    return 1 ;;
            esac
            ;;
        esac
        ;;
    .)  print -r -- "$TITLE_TEXT"
        return 0
        ;;
    =)  shift
        t="$*"
        ;;
    *)  t="$*"
        ;;
    esac
    export TITLE_TEXT="$t"
    eval x=\"$t\"
    case $TERM in
    630*)           print -nr -- $'\E[?'"${#x}"$';0v'"${x}" ;;
    uwin*|*vt100|xterm*)    print -nr -- $'\E]0;'"${x}"$'\a' ;;
    *)          return 1 ;;
    esac
    return 0
}