(octave.info)Executable Octave Programs

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2.6 Executable Octave Programs
==============================

Once you have learned Octave, you may want to write self-contained
Octave scripts, using the ‘#!’ script mechanism.  You can do this on GNU
systems and on many Unix systems (1).

   Self-contained Octave scripts are useful when you want to write a
program which users can invoke without knowing that the program is
written in the Octave language.  Octave scripts are also used for batch
processing of data files.  Once an algorithm has been developed and
tested in the interactive portion of Octave, it can be committed to an
executable script and used again and again on new data files.

   As a trivial example of an executable Octave script, you might create
a text file named ‘hello’, containing the following lines:

     #! OCTAVE-INTERPRETER-NAME -qf
     # a sample Octave program
     printf ("Hello, world!\n");

(where OCTAVE-INTERPRETER-NAME should be replaced with the full path and
name of your Octave binary).  Note that this will only work if ‘#!’
appears at the very beginning of the file.  After making the file
executable (with the ‘chmod’ command on Unix systems), you can simply
type:

     hello

at the shell, and the system will arrange to run Octave as if you had
typed:

     octave hello

   The line beginning with ‘#!’ lists the full path and filename of an
interpreter to be run, and an optional initial command line argument to
pass to that interpreter.  The operating system then runs the
interpreter with the given argument and the full argument list of the
executed program.  The first argument in the list is the full filename
of the Octave executable.  The rest of the argument list will either be
options to Octave, or data files, or both.  The ‘-qf’ options are
usually specified in stand-alone Octave programs to prevent them from
printing the normal startup message, and to keep them from behaving
differently depending on the contents of a particular user’s
‘~/.octaverc’ file.  Note: Invoking Octave from the Command Line.

   Note that some operating systems may place a limit on the number of
characters that are recognized after ‘#!’.  Also, the arguments
appearing in a ‘#!’ line are parsed differently by various
shells/systems.  The majority of them group all the arguments together
in one string and pass it to the interpreter as a single argument.  In
this case, the following script:

     #! OCTAVE-INTERPRETER-NAME -q -f # comment

is equivalent to typing at the command line:

     octave "-q -f # comment"

which will produce an error message.  Unfortunately, it is not possible
for Octave to determine whether it has been called from the command line
or from a ‘#!’ script, so some care is needed when using the ‘#!’
mechanism.

   Note that when Octave is started from an executable script, the
built-in function ‘argv’ returns a cell array containing the command
line arguments passed to the executable Octave script, not the arguments
passed to the Octave interpreter on the ‘#!’ line of the script.  For
example, the following program will reproduce the command line that was
used to execute the script, not ‘-qf’.

     #! /bin/octave -qf
     printf ("%s", program_name ());
     arg_list = argv ();
     for i = 1:nargin
       printf (" %s", arg_list{i});
     endfor
     printf ("\n");

   ---------- Footnotes ----------

   (1) The ‘#!’ mechanism works on Unix systems derived from Berkeley
Unix, System V Release 4, and some System V Release 3 systems.