If starting from Workbench you can specify the window-description
and the startup script (default S:ZStart , see above) with ToolTypes:
eg.     WINDOW=con:20/50/400/100/Moin
        SCRIPT=ram:hello
        WINDOW=             {this would not open a window}
Make sure that WINDOW and SCRIPT are in capital letters.
(You can edit the ToolTypes by selecting an icon and then choosing
"Information" from the Workbench-Menu.)

All ToolTypes:
 SCRIPT=name : Start script named "name" (default S:ZStart)
 WINDOW=desc : Open window with window-description "desc"
 COMMAND=cmd : Start command named "cmd"
 NORAW=      : Switches off the internal  command-line-editing 
 ICONNAME=name : Specify name of the icon for  iconifying  (OS2.0+)
 XPOS=number : Give the position of the icon (OS2.0+)
 YPOS=number : Give the position of the icon (OS2.0+)
 ICONIFY=    : Start in iconifyed mode (OS2.0+)
 SCREEN=depth/displayID/overscan/title : Opens a  Public Screen  (OS2.0+)
 HELPMAN=file: Determine the file (with path) of the online help (default: S:ZShell.doc)

These two are handled by Workbench 2.0+:
 DONOTWAIT   : Use this if you put ZShell in the WBStartup-drawer
               (preferably together with the ICONIFY ToolType)
 TOOLPRI=pri : Sets the  priority  of the process