Passing Arguments from Command Line into a Tcl Script

In addition to the above answer, I found the following helpful:

For running within QuestaSim/ModelSim/Quartus I followed the following resource:

Typically we can run .tcl scripts with the source command, but this doesn't inherently process arguments like base .tcl scripts can use normally. So by using a process, you can achieve the same thing.

For demonstrating how to pass arguments from the command line into a TCL script:

Create a text file named args.tcl that contains the following commands:

# If no command line arguments are passed perform no actions
if {$argc > 0} {
# argv0 conatins the filename of the script
puts "The name of the script is: $argv0"
# argc contains the count of the arguments passed
puts "Total count of arguments passed is: $argc"
# argv contains a list of the arguments
puts "The arguments passed are: $argv"
# Using the List Index of argv print a specific argument
puts "The first argument passed was [lindex $argv 0]"
}

After you have created the file invoke the script with the following command line:

> Tclsh85 args.Tcl ONE 2 3
The name of the script is: args.Tcl
Total count of arguments passed is: 3
The arguments passed are: ONE 2 3
The first argument passed was ONE
>

Reference: Tcl/Tk 8.5 Programming Cookbook

I find that it's often easiest to parse arguments (the useful ones of which are always passed as a list in the global argv variable, with the length of that list in the global argc variable; C programmers will recognise the names) like this:

switch $argc {
    2 {
        # Split the arguments and set the default for the optional
        lassign $argv firstArg secondArg
        set thirdArg "default value"
    }
    3 {
        # Split all the arguments
        lassign $argv firstArg secondArg thirdArg
    }
    default {
        # Oh no! Give the user an error message and stop
        error "wrong # args: should be \"$argv0 firstArg secondArg ?thirdArg?\""
    }
}

The global argv0 is the name of the script. Properly it would be one of the arguments in argv/argc (along with potentially the name of the Tcl interpreter) but almost nobody usually uses it in the same way so it is split out for you. As I said, the useful arguments are in argv.

You can also use any other list handling command with argv; foreach works great for a sequence of filenames, for example.