Executing a macro string variable as a command using DOCOMMAND

The macro command, DOCOMMAND, executes a macro string variable as a command. This enables you to construct a command from string variables and then have that command run as a macro statement. Suppose you have a function to create a copy of a boundary and then fit arcs to the copy:

FUNCTION CopyAndArcfit(ENTITY Ent) {
    STRING $NewName = new_entity_name('boundary')
    COPY BOUNDARY $Ent
    EDIT BOUNDARY $NewName ARCFIT 0.01
}

If you then want to use the same function to copy a pattern and then fit arcs to the copy. You can replace all instances of 'boundary' with 'pattern' when you give the function a pattern entity. Unfortunately you cannot do this by using variables directly because the PowerMill command syntax does not allow variable substitution in network KEYWORDS for example you cannot use $Type like this:

COPY $Type $Ent

However, you can build the command as a string and then use DOCOMMAND to execute the resulting string as a command:

FUNCTION CopyAndArcFit(Entity Ent) {
    STRING $NewName = new_entity_name(Ent.RootType)
    STRING Cmd = "COPY "+ Ent.RootType + " " + Ent.name
    DOCOMMAND $Cmd
    $Cmd = "EDIT " + Ent.RootType + " " + Newname + " ARCFIT 0.01"
    DOCOMMAND $Cmd
}

You can use this technique whenever you find that a variable value cannot be used in a particular point in a command.