Program components

SCO Visual Tcl Reference Guide
Chapter 3, SCO Visual Tcl - graphical scripting language

Program components

SCO Visual Tcl has three executable binary components:

vtcl: The SCO Visual Tcl interpreter that is executed on a per-script basis.
xm_vtcld: The SCO Visual Tcl server (running as a daemon) that invokes the GUI (OSF/Motif) calls.
cm_vtcld: The SCO Visual Tcl server that invokes the curses calls.

The vtcl process interprets the SCO Visual Tcl script and sends commands over a communications channel to the appropriate SCO Visual Tcl server. The server interprets the commands received and makes appropriate calls to the underlying display system.

In graphical mode (running under OSF/Motif on an X server), there is only one xm_vtcld daemon per display and user. A single xm_vtcld process may have several vtcl processes sending it commands. The daemon remains active until the user associated with the daemon logs out or the daemon is explicitly killed. Consequently, after the first application is invoked, all subsequent SCO Visual Tcl applications can start up faster, since the initialization of the server need only be performed once. In contrast, in character mode (running under curses on a character terminal), there is one cm_vtcld process for each vtcl process.

This means that with use of the graphical SCO Visual Tcl, multiple scripts may be interacting with a single display, but with the character SCO Visual Tcl, only a single script may be interacting with the terminal at any one time.

SCO Visual Tcl will automatically run in character mode (that is, run the cm_vtcld process) on character terminals. To have the vtcl script run in character mode on graphical displays (for example, ScoTerm), the environment variable CHARM must be set to TRUE or the environment variable DISPLAY needs to be unset.