Getting Started
***************

This chapter explains some of Octave's basic features, including how to start an Octave session, get help at the command prompt, edit the command line, and write Octave programs that can be executed as commands from your shell.

Invoking Octave from the Command Line
=====================================

Normally, Octave is used interactively by running the program octave without any arguments.  Once started, Octave reads commands from the terminal until you tell it to exit.

You can also specify the name of a file on the command line, and Octave will read and execute the commands from the named file and then exit when it is finished.

You can further control how Octave starts by using the command-line options described in the next section, and Octave itself can remind you of the options available.  Type octave --help to display all available options and briefly describe their use (octave -h is a shorter equivalent).

Command Line Options
--------------------

Here is a complete list of all the command line options that Octave accepts.

--debug
-d
     Enter parser debugging mode.  Using this option will cause Octave's parser to print a lot of information about the commands it reads, and is probably only useful if you are actually trying to debug the parser.

--echo-commands
-x
     Echo commands as they are executed.

--eval CODE
     Evaluate CODE and exit when done unless --persist is also specified.

--exec-path PATH
     Specify the path to search for programs to run.  The value of PATH specified on the command line will override any value of OCTAVE_EXEC_PATH found in the environment, but not any commands in the system or user startup files that set the built-in variable EXEC_PATH.

--help
-h
-?
     Print short help message and exit.

--image-path PATH
     Specify the path to search for images.  The value of PATH specified on the command line will set the value of IMAGE_PATH found in the environment.

--info-file FILENAME
     Specify the name of the info file to use.  The value of FILENAME specified on the command line will override any value of OCTAVE_INFO_FILE found in the environment, but not any commands in the system or user startup files that use the the info_file function.

--info-program PROGRAM
     Specify the name of the info program to use.  The value of PROGRAM specified on the command line will override any value of OCTAVE_INFO_PROGRAM found in the environment, but not any commands in the system or user startup files that use the info_program function.

--interactive
-i
     Force interactive behavior.  This can be useful for running Octave via a remote shell command or inside an Emacs shell buffer.  For another way to run Octave within Emacs, see Emacs.

--no-history
-H
     Disable command-line history.

--no-init-file
     Don't read the ~/.octaverc or .octaverc files.

--no-line-editing
     Disable command-line editing.

--no-site-file
     Don't read the site-wide octaverc file.

--norc
-f
     Don't read any of the system or user initialization files at startup. This is equivalent to using both of the options --no-init-file and --no-site-file.

--path PATH
-p PATH
     Specify the path to search for function files.  The value of PATH specified on the command line will override any value of OCTAVE_PATH found in the environment, but not any commands in the system or user startup files that set the internal variable LOADPATH through one of the path functions.

--persist
     Go to interactive mode after --eval or reading from a file named on the command line.

--silent
--quiet
-q
     Don't print the usual greeting and version message at startup.

--traditional
--braindead
     For compatibility with MATLAB, set initial values for user-preferences to the following values

            PS1                             = ">> "
            PS2                             = ""
            beep_on_error                   = true
            crash_dumps_octave_core         = false
            default_save_options            = "-mat-binary"
            fixed_point_format              = true
            history_timestamp_format_string = "%%-- %D %I:%M %p --%%"
            page_screen_output              = false
            print_empty_dimensions          = false

     and disable the following warnings

            Octave:fopen-file-in-path
            Octave:function-name-clash
            Octave:load-file-in-path

--verbose
-V
     Turn on verbose output.

--version
-v
     Print the program version number and exit.

FILE
     Execute commands from FILE.  Exit when done unless --persist is also specified.

Octave also includes several built-in variables that contain information about the command line, including the number of arguments and all of the options.

(argv)

(program_name)

(program_invocation_name)

Here is an example of using these functions to reproduce Octave's command line.

     printf ("%s", program_name ());
     arg_list = argv ();
     for i = 1:nargin
       printf (" %s", arg_list{i});
     endfor
     printf ("\n");

See Index Expressions, for an explanation of how to properly index arrays of strings and substrings in Octave, and see Defining Functions, for information about the variable nargin.

Startup Files
-------------

When Octave starts, it looks for commands to execute from the files in the following list. These files may contain any valid Octave commands, including function definitions.

OCTAVE-HOME/share/octave/site/m/startup/octaverc
     Where OCTAVE-HOME is the directory in which all of Octave is installed (the default is OCTAVEHOME).  This file is provided so that changes to the default Octave environment can be made globally for all users at your site for all versions of Octave you have installed.  Some care should be taken when making changes to this file, since all users of Octave at your site will be affected.

OCTAVE-HOME/share/octave/VERSION/m/startup/octaverc
     Where OCTAVE-HOME is the directory in which all of Octave is installed (the default is OCTAVEHOME), and VERSION is the version number of Octave.  This file is provided so that changes to the default Octave environment can be made globally for all users for a particular version of Octave.  Some care should be taken when making changes to this file, since all users of Octave at your site will be affected.

~/.octaverc
     This file is normally used to make personal changes to the default Octave environment.

.octaverc
     This file can be used to make changes to the default Octave environment for a particular project.  Octave searches for this file in the current directory after it reads ~/.octaverc.  Any use of the cd command in the ~/.octaverc file will affect the directory that Octave searches for the file .octaverc.

     If you start Octave in your home directory, commands from from the file ~/.octaverc will only be executed once.

A message will be displayed as each of the startup files is read if you invoke Octave with the --verbose option but without the --silent option.

(OCTAVE_HOME)

(version)

(ver)

Quitting Octave
===============

(quit)

(atexit)

Commands for Getting Help
=========================

The entire text of this manual is available from the Octave prompt via the command doc.  In addition, the documentation for individual user-written functions and variables is also available via the help command.  This section describes the commands used for reading the manual and the documentation strings for user-supplied functions and variables.  See Function Files, for more information about how to document the functions you write.

(help)

(doc)

(lookfor)

The following function can be used to change which programs are used for displaying the documentation, and where the documentation can be found.

(info_file)

(info_program)

(makeinfo_program)

(suppress_verbose_help_message)

Command Line Editing
====================

Octave uses the GNU readline library to provide an extensive set of command-line editing and history features.  Only the most common features are described in this manual.  Please see The GNU Readline Library manual for more information.

To insert printing characters (letters, digits, symbols, etc.), simply type the character.  Octave will insert the character at the cursor and advance the cursor forward.

Many of the command-line editing functions operate using control characters.  For example, the character Control-a moves the cursor to the beginning of the line.  To type C-a, hold down CTRL and then press a.  In the following sections, control characters such as Control-a are written as C-a.

Another set of command-line editing functions use Meta characters.  On some terminals, you type M-u by holding down META and pressing u.  If your terminal does not have a META key, you can still type Meta charcters using two-character sequences starting with ESC.  Thus, to enter M-u, you could type ESCu.  The ESC character sequences are also allowed on terminals with real Meta keys.  In the following sections, Meta characters such as Meta-u are written as M-u.

Cursor Motion
-------------

The following commands allow you to position the cursor.

C-b
     Move back one character.

C-f
     Move forward one character.

DEL
     Delete the character to the left of the cursor.

C-d
     Delete the character underneath the cursor.

M-f
     Move forward a word.

M-b
     Move backward a word.

C-a
     Move to the start of the line.

C-e
     Move to the end of the line.

C-l
     Clear the screen, reprinting the current line at the top.

C-_
C-/
     Undo the last thing that you did.  You can undo all the way back to an empty line.

M-r
     Undo all changes made to this line.  This is like typing the `undo' command enough times to get back to the beginning.

The above table describes the most basic possible keystrokes that you need in order to do editing of the input line.  On most terminals, you can also use the arrow keys in place of C-f and C-b to move forward and backward.

Notice how C-f moves forward a character, while M-f moves forward a word.  It is a loose convention that control keystrokes operate on characters while meta keystrokes operate on words.

The function clc will allow you to clear the screen from within Octave programs.

(clc)

Killing and Yanking
-------------------

Killing text means to delete the text from the line, but to save it away for later use, usually by yanking it back into the line. If the description for a command says that it `kills' text, then you can be sure that you can get the text back in a different (or the same) place later.

Here is the list of commands for killing text.

C-k
     Kill the text from the current cursor position to the end of the line.

M-d
     Kill from the cursor to the end of the current word, or if between words, to the end of the next word.

M-DEL
     Kill from the cursor to the start of the previous word, or if between words, to the start of the previous word.

C-w
     Kill from the cursor to the previous whitespace.  This is different than M-DEL because the word boundaries differ.

And, here is how to yank the text back into the line.  Yanking means to copy the most-recently-killed text from the kill buffer.

C-y
     Yank the most recently killed text back into the buffer at the cursor.

M-y
     Rotate the kill-ring, and yank the new top.  You can only do this if the prior command is C-y or M-y.

When you use a kill command, the text is saved in a kill-ring. Any number of consecutive kills save all of the killed text together, so that when you yank it back, you get it in one clean sweep.  The kill ring is not line specific; the text that you killed on a previously typed line is available to be yanked back later, when you are typing another line.

Commands For Changing Text
--------------------------

The following commands can be used for entering characters that would otherwise have a special meaning (e.g., TAB, C-q, etc.), or for quickly correcting typing mistakes.

C-q
C-v
     Add the next character that you type to the line verbatim.  This is how to insert things like C-q for example.

M-TAB
     Insert a tab character.

C-t
     Drag the character before the cursor forward over the character at the cursor, also moving the cursor forward.  If the cursor is at the end of the line, then transpose the two characters before it.

M-t
     Drag the word behind the cursor past the word in front of the cursor moving the cursor over that word as well.

M-u
     Uppercase the characters following the cursor to the end of the current (or following) word, moving the cursor to the end of the word.

M-l
     Lowercase the characters following the cursor to the end of the current (or following) word, moving the cursor to the end of the word.

M-c
     Uppercase the character following the cursor (or the beginning of the next word if the cursor is between words), moving the cursor to the end of the word.

Letting Readline Type For You
-----------------------------

The following commands allow Octave to complete command and variable names for you.

TAB
     Attempt to do completion on the text before the cursor.  Octave can complete the names of commands and variables.

M-?
     List the possible completions of the text before the cursor.

(completion_append_char)

(completion_matches)

Commands For Manipulating The History
-------------------------------------

Octave normally keeps track of the commands you type so that you can recall previous commands to edit or execute them again.  When you exit Octave, the most recent commands you have typed, up to the number specified by the variable history_size, are saved in a file. When Octave starts, it loads an initial list of commands from the file named by the variable history_file.

Here are the commands for simple browsing and searching the history list.

LFD
RET
     Accept the line regardless of where the cursor is.  If this line is non-empty, add it to the history list.  If this line was a history line, then restore the history line to its original state.

C-p
     Move `up' through the history list.

C-n
     Move `down' through the history list.

M-<
     Move to the first line in the history.

M->
     Move to the end of the input history, i.e., the line you are entering!

C-r
     Search backward starting at the current line and moving `up' through the history as necessary.  This is an incremental search.

C-s
     Search forward starting at the current line and moving `down' through the history as necessary.

On most terminals, you can also use the arrow keys in place of C-p and C-n to move through the history list.

In addition to the keyboard commands for moving through the history list, Octave provides three functions for viewing, editing, and re-running chunks of commands from the history list.

(history)

(edit_history)

(run_history)

Octave also allows you customize the details of how and where the history is saved.

(history_file)

(history_size)

(saving_history)

(history_timestamp_format_string)

(EDITOR)

Customizing readline
--------------------

As mentioned earlier Octave uses the GNU readline library for command-line editing and history features. It is possible to customize how readline works through a configuration file.

(read_readline_init_file)

Customizing the Prompt
----------------------

The following variables are available for customizing the appearance of the command-line prompts.  Octave allows the prompt to be customized by inserting a number of backslash-escaped special characters that are decoded as follows:

\t
     The time.

\d
     The date.

\n
     Begins a new line by printing the equivalent of a carriage return followed by a line feed.

\s
     The name of the program (usually just octave).

\w
     The current working directory.

\W
     The basename of the current working directory.

\u
     The username of the current user.

\h
     The hostname, up to the first `.'.

\H
     The hostname.

\#
     The command number of this command, counting from when Octave starts.

\!
     The history number of this command.  This differs from \# by the number of commands in the history list when Octave starts.

\$
     If the effective UID is 0, a #, otherwise a $.

\nnn
     The character whose character code in octal is NNN.

\\
     A backslash.

(PS1)

(PS2)

(PS4)

Diary and Echo Commands
-----------------------

Octave's diary feature allows you to keep a log of all or part of an interactive session by recording the input you type and the output that Octave produces in a separate file.

(diary)

Sometimes it is useful to see the commands in a function or script as they are being evaluated.  This can be especially helpful for debugging some kinds of problems.

(echo)

(echo_executing_commands)

How Octave Reports Errors
=========================

Octave reports two kinds of errors for invalid programs.

A parse error occurs if Octave cannot understand something you have typed.  For example, if you misspell a keyword,

     octave:13> functon y = f (x) y = x^2; endfunction

Octave will respond immediately with a message like this:

     parse error:

       functon y = f (x) y = x^2; endfunction
               ^

For most parse errors, Octave uses a caret (^) to mark the point on the line where it was unable to make sense of your input.  In this case, Octave generated an error message because the keyword function was misspelled.  Instead of seeing function f, Octave saw two consecutive variable names, which is invalid in this context.  It marked the error at y because the first name by itself was accepted as valid input.

Another class of error message occurs at evaluation time.  These errors are called run-time errors, or sometimes evaluation errors because they occur when your program is being run, or evaluated.  For example, if after correcting the mistake in the previous function definition, you type

     octave:13> f ()

Octave will respond with

     error: `x' undefined near line 1 column 24
     error: evaluating expression near line 1, column 24
     error: evaluating assignment expression near line 1, column 22
     error: called from `f'

This error message has several parts, and gives you quite a bit of information to help you locate the source of the error.  The messages are generated from the point of the innermost error, and provide a traceback of enclosing expressions and function calls.

In the example above, the first line indicates that a variable named x was found to be undefined near line 1 and column 24 of some function or expression.  For errors occurring within functions, lines are counted from the beginning of the file containing the function definition.  For errors occurring at the top level, the line number indicates the input line number, which is usually displayed in the prompt string.

The second and third lines in the example indicate that the error occurred within an assignment expression, and the last line of the error message indicates that the error occurred within the function f. If the function f had been called from another function, for example, g, the list of errors would have ended with one more line:

     error: called from `g'

These lists of function calls usually make it fairly easy to trace the path your program took before the error occurred, and to correct the error before trying again.

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

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.

For example, you could 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 file name for your Octave binary).  Note that this will only work if #! appears at the very beginning of the file. After making this file executable (with the chmod command), 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 file name 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 file name of the Octave program. The rest of the argument list will either be options to Octave, or data files, or both.  The -qf option is 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.  See 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 various shells/systems parse differently the arguments appearing in a #! line.  The majority of them group together all the arguments in a string and pass it to the interepreter as a single argument.  In this case, the following script:

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

is equivalent to type at the command line:

     octave "-q -f # comment"

which would obviously produce an error message.  Unfortunately, it is impossible for Octave to know 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 an 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 is used to execute 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");

Comments in Octave Programs
===========================

A comment is some text that is included in a program for the sake of human readers, and that is not really part of the program.  Comments can explain what the program does, and how it works.  Nearly all programming languages have provisions for comments, because programs are typically hard to understand without them.

In the Octave language, a comment starts with either the sharp sign character, #, or the percent symbol % and continues to the end of the line.  The Octave interpreter ignores the rest of a line following a sharp sign or percent symbol.  For example, we could have put the following into the function f:

     function xdot = f (x, t)

     # usage: f (x, t)
     #
     # This function defines the right hand
     # side functions for a set of nonlinear
     # differential equations.

       r = 0.25;
       ...
     endfunction

The help command (see Getting Help) is able to find the first block of comments in a function (even those that are composed directly on the command line).  This means that users of Octave can use the same commands to get help for built-in functions, and for functions that you have defined.  For example, after defining the function f above, the command help f produces the output

      usage: f (x, t)

      This function defines the right hand
      side functions for a set of nonlinear
      differential equations.

Although it is possible to put comment lines into keyboard-composed throw-away Octave programs, it usually isn't very useful, because the purpose of a comment is to help you or another person understand the program at a later time.