Running Programs

KerboScript supports running executing code saved in files on the local or archive disks. The terms “program” and “script” are generally used interchangably when describing this behavior. Programs can either be run using one of the Run Functions or the Run Keyword. Supported file types are:

Raw Text KerboScript files
These files contain KerboScript text commands, as if you had typed them directly into the terminal. They are easily read, written, and edited by humans. These files traditionally have a ".ks" extension, however it is not required.
Compiled Machine Language Files
These files contain encoded and compressed machine language opcodes. They are not formatted to allow humans to read, write, or edit the files. These files traditionally have a ".ksm" extension, however it is not required.

See also

KerboScript Machine Code
An explaination of how scripts are compiled, as well as an explaination of how COMPILE stores opcodes.
Filename Warning
Warning detailing issues with case sensitive host file systems.


If you attempt to run the same program twice from within another script, the previously compiled version will be executed without attempting to recompile even if the original source script has been modified. However once the program has finished executing and returns to the main terminal input, the memory containing the programs is released. This means that every time that a script file is run from the terminal it is recompiled, even if the script file has not changed.

Run Functions


Changed in version 1.0.0: The RUNPATH and RUNONCEPATH functions were added in version 1.0.0. Previously, only the more limited RUN command existed.

RUNPATH(path, commaSeperatedArgs...)
RUNONCEPATH(path, commaSeperatedArgs...)
  • path (String or Path) – Path information pointing to the script file. May be an Absolute or Relative path.
  • commaSeperatedArgs... (Optional) – A comma seperated list of arguments to pass to the program


The RUNPATH or RUNONCEPATH functions are nearly identical to each other except for what is described below under the heading Running a program “ONCE”.

RUNPATH or RUNONCEPATH take a list of arguments, the first of which is the filename of the program to run, and must evaluate to a string. Any additional arguments after that are optional, and are passed in to the program as its parameters it can read:

RUNPATH( "myfile.ks" ). // Run a program called myfile.ks.
RUNPATH( "myfile" ). // Run a program called myfile, where kOS will guess
                     // the filename extension you meant, and probably
                     // pick ".ks" for you.
RUNPATH( "myfile.ks", 1, 2 ). // Run a program called myfile.ks, and
                              // pass in the values 1 and 2 as its first
                              // two parameters.

RUNPATH or RUNONCEPATH can also work with any expression for the filename as long as it results in a string:

SET file_base to "prog_num_".
SET file_num to 3.
SET file_ending to ".ks".
RUNPATH( file_base + file_num + file_ending, 1, 2 ).
    // The above has the same effect as if you had done:
    RUNPATH("prog_num_3.ks", 1, 2).

Run Keyword


You should prefer RUNPATH over RUN

The RUN command is older, and less powerful than the newer Run Functions, and is kept around mostly for backward compatibility. You can’t use a variable or expression to refer to the file name. The following examples will throw exceptions (but are compatible with the Run Functions):

SET filename_variable TO "myfile.ks".
RUN filename_variable. // Error: a file called "filename_variable" not found.

RUN "my" + "file" + ".ks".  // Syntax error - a single literal string expected,
                            // not an expression that returns a string.

Due to a parsing ambiguity issue, it was impossible to make RUN work with any arbitrary expression as the filename without changing its syntax a little in a way that would break every old kOS script. Therefore it was deemed better to just add a new function that uses the new syntax instead of changing the syntax of RUN.

RUN [ONCE] path [(commaSeperatedArgs...)]
  • once – By using the optional ONCE keyword parameter you can modify the behavior of the RUN keyword to obey the run once logic
  • path (String or bare word literal) – The string (i.e. "filename.ks") describing the path pointing to the script file. May be an Absolute or Relative path.
  • commaSeperatedArgs... (Optional) – A comma seperated list of arguments to pass to the program, surrounded by parenthesis (i.e. (arg1, arg2))

The RUN keyword is only capable of using hard-coded program names that were known at the time you wrote the script, and expressed as a simple bare word or literal string in quotes. For example, you can do this:

RUN "myfile.ks".
RUN myfile.ks. // using a bare word literal string

If you wish to pass arguments to the program, you may optionally add a set of parentheses with an argument list to the end of the syntax, like so:

// All 3 of these work:
RUN myfile(1,2,3).
RUN myfile.ks(1,2,3).
RUM "myfile.ks"(1,2,3).

Details Of Running Programs

Running a program “ONCE”

If the RUNONCEPATH function is used instead of the RUNPATH function, or the optional ONCE keyword is added to the RUN command, it means the run will not actually occur if the program has already been run once during the current program context. This is intended mostly for loading library program files that may have mainline code in them for initialization purposes that you don’t want to get run a second time just because you use the library in two different subprograms.

RUN ONCE and RUNONCEPATH mean “Run unless it’s already been run, in which case skip it.”


The “ONCE” component has no effect on how frequently a given program is compiled. Every unique program is compiled exactly once per program context execution, and remains in memory until the program finishes and returns control to the terminal.

Automatic guessing of full filename

For all 3 types of run command (RUN, RUNPATH, and RUNONCEPATH), the following filename “guess” rules are used when the filename given is incomplete:

  • 1: If no path information was present in the filename, then assume the file is in the current directory (that’s pretty much standard for all filename commands).
  • 2: Assume if no filename extension such as ".ks" or ".ksm" was given, and there is no file found that lacks an extension in the way the filename was given, then first try to find a file with the ”.ksm” extension appended to it, and if that file is not found then try to find a file with the ”.ks” extension appended to it.


Although the syntax is a bit different for RUN versus RUNPATH (and RUNONCEPATH), all 3 techniques allow you to pass arguments into the program that it sees as its main script parameter values.

The following commands do equivalent things:

RUN "AutoLaunch.ks"( 75000, true, "hello" ).
RUNPATH("AutoLaunch.ksm", 75000, true, "hello" ).

In both of the above examples, had the program “AutoLaunch.ks” started with these lines:

// AutoLaunch.ks program file:
parameter final_alt, do_countdown, message.
// rest of program not shown...

Then inside AutoLaunch.ks, final_alt would be 75000, and do_countdown would be true, and message would be "hello".