(octave.info)Script Files


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11.10 Script Files
==================

A script file is a file containing (almost) any sequence of Octave
commands.  It is read and evaluated just as if you had typed each
command at the Octave prompt, and provides a convenient way to perform a
sequence of commands that do not logically belong inside a function.

   Unlike a function file, a script file must _not_ begin with the
keyword ‘function’.  If it does, Octave will assume that it is a
function file, and that it defines a single function that should be
evaluated as soon as it is defined.

   A script file also differs from a function file in that the variables
named in a script file are not local variables, but are in the same
scope as the other variables that are visible on the command line.

   Even though a script file may not begin with the ‘function’ keyword,
it is possible to define more than one function in a single script file
and load (but not execute) all of them at once.  To do this, the first
token in the file (ignoring comments and other white space) must be
something other than ‘function’.  If you have no other statements to
evaluate, you can use a statement that has no effect, like this:

     # Prevent Octave from thinking that this
     # is a function file:

     1;

     # Define function one:

     function one ()
       ...

   To have Octave read and compile these functions into an internal
form, you need to make sure that the file is in Octave’s load path
(accessible through the ‘path’ function), then simply type the base name
of the file that contains the commands.  (Octave uses the same rules to
search for script files as it does to search for function files.)

   If the first token in a file (ignoring comments) is ‘function’,
Octave will compile the function and try to execute it, printing a
message warning about any non-whitespace characters that appear after
the function definition.

   Note that Octave does not try to look up the definition of any
identifier until it needs to evaluate it.  This means that Octave will
compile the following statements if they appear in a script file, or are
typed at the command line,

     # not a function file:
     1;
     function foo ()
       do_something ();
     endfunction
     function do_something ()
       do_something_else ();
     endfunction

even though the function ‘do_something’ is not defined before it is
referenced in the function ‘foo’.  This is not an error because Octave
does not need to resolve all symbols that are referenced by a function
until the function is actually evaluated.

   Since Octave doesn’t look for definitions until they are needed, the
following code will always print ‘bar = 3’ whether it is typed directly
on the command line, read from a script file, or is part of a function
body, even if there is a function or script file called ‘bar.m’ in
Octave’s path.

     eval ("bar = 3");
     bar

   Code like this appearing within a function body could fool Octave if
definitions were resolved as the function was being compiled.  It would
be virtually impossible to make Octave clever enough to evaluate this
code in a consistent fashion.  The parser would have to be able to
perform the call to ‘eval’ at compile time, and that would be impossible
unless all the references in the string to be evaluated could also be
resolved, and requiring that would be too restrictive (the string might
come from user input, or depend on things that are not known until the
function is evaluated).

   Although Octave normally executes commands from script files that
have the name ‘FILE.m’, you can use the function ‘source’ to execute
commands from any file.

 -- : source (FILE)
 -- : source (FILE, CONTEXT)
     Parse and execute the contents of FILE.

     Without specifying CONTEXT, this is equivalent to executing
     commands from a script file, but without requiring the file to be
     named ‘FILE.m’ or to be on the execution path.

     Instead of the current context, the script may be executed in
     either the context of the function that called the present function
     ("caller"), or the top-level context ("base").

     See also: Note: run.

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