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System Utilities

This chapter describes the functions that are available to allow you to get information about what is happening outside of Octave, while it is still running, and use this information in your program. For example, you can get information about environment variables, the current time, and even start other programs from the Octave prompt.

Timing Utilities

Loadable Function: time (): Return the current time as the number of seconds since the epoch. The epoch is referenced to 00:00:00 CUT (Coordinated Universal Time) 1 Jan 1970.

Several of Octave's time functions a data structure for time that includes the following elements:

usec: Microseconds after the second (0-999999).
sec: Seconds after the minute (0-61). This number can be 61 to account for leap seconds.
min: Minutes after the hour (0-59).
hour: Hours since midnight (0-23).
mday: Day of the month (1-31).
mon: Months since January (0-11).
year: Years since 1900.
wday: Days since Sunday (0-6).
yday: Days since January 1 (0-365).
isdst: Daylight Savings Time flag.
zone: Time zone.

Loadable Function: mktime (time_struct): Convert a time structure to the number of seconds since the epoch.

Loadable Function: localtime (t): Given a value returned from time (or any nonnegative integer), return a time structure corresponding to the local time zone.

Loadable Function: gmtime (t): Given a value returned from time (or any nonnegative integer), return a time structure corresponding to CUT.

Function File: asctime (time_struct): Convert a time structure to a string using the following five-field format: Thu Mar 28 08:40:14 1996. The function ctime (time) is equivalent to asctime (localtime (time)).

Loadable Function: strftime (time_struct)

Format a time structure in a flexible way using `%' substitutions similar to those in printf. Except where noted, substituted fields have a fixed size; numeric fields are padded if necessary. Padding is with zeros by default; for fields that display a single number, padding can be changed or inhibited by following the `%' with one of the modifiers described below. Unknown field specifiers are copied as normal characters. All other characters are copied to the output without change.

Octave's strftime function supports a superset of the ANSI C field specifiers.

Literal character fields:

%: % character.
n: Newline character.
t: Tab character.

Numeric modifiers (a nonstandard extension):

-: Do not pad the field.
_: Pad the field with spaces.

Time fields:

%H: Hour (00-23).
%I: Hour (01-12).
%k: Hour (0-23).
%l: Hour (1-12).
%M: Minute (00-59).
%p: Locale's AM or PM.
%r: Time, 12-hour (hh:mm:ss [AP]M).
%R: Time, 24-hour (hh:mm).
%s: Time in seconds since 00:00:00, Jan 1, 1970 (a nonstandard extension).
%S: Second (00-61).
%T: Time, 24-hour (hh:mm:ss).
%X: Locale's time representation (%H:%M:%S).
%Z: Time zone (EDT), or nothing if no time zone is determinable.

Date fields:

%a: Locale's abbreviated weekday name (Sun-Sat).
%A: Locale's full weekday name, variable length (Sunday-Saturday).
%b: Locale's abbreviated month name (Jan-Dec).
%B: Locale's full month name, variable length (January-December).
%c: Locale's date and time (Sat Nov 04 12:02:33 EST 1989).
%C: Century (00-99).
%d: Day of month (01-31).
%e: Day of month ( 1-31).
%D: Date (mm/dd/yy).
%h: Same as %b.
%j: Day of year (001-366).
%m: Month (01-12).
%U: Week number of year with Sunday as first day of week (00-53).
%w: Day of week (0-6).
%W: Week number of year with Monday as first day of week (00-53).
%x: Locale's date representation (mm/dd/yy).
%y: Last two digits of year (00-99).
%Y: Year (1970-).

Function File: clock ()

Return a vector containing the current year, month (1-12), day (1-31), hour (0-23), minute (0-59) and second (0-61). For example,

octave:13> clock
ans =

  1993     8    20     4    56     1

The function clock is more accurate on systems that have the gettimeofday function.

Function File: date ()

Returns the date as a character string in the form DD-MMM-YY. For example,

octave:13> date
ans = 20-Aug-93

Function File: tic ()

Function File: toc ()

These functions set and check a wall-clock timer. For example,

tic ();
# many computations later...
elapsed_time = toc ();

will set the variable elapsed_time to the number of seconds since the most recent call to the function tic.

Function File: etime (t1, t2)

Return the difference (in seconds) between two time values returned from clock. For example:

t0 = clock ();
# many computations later...
elapsed_time = etime (clock (), t0);

will set the variable elapsed_time to the number of seconds since the variable t0 was set.

Built-in Function: [total, user, system] = cputime ();: Return the CPU time used by your Octave session. The first output is the total time spent executing your process and is equal to the sum of second and third outputs, which are the number of CPU seconds spent executing in user mode and the number of CPU seconds spent executing in system mode, respectively. If your system does not have a way to report CPU time usage, cputime returns 0 for each of its output values.

Function File: is_leap_year (year)

Return 1 if the given year is a leap year and 0 otherwise. If no arguments are provided, is_leap_year will use the current year. For example,

octave:13> is_leap_year (2000)
ans = 1

Filesystem Utilities

Octave includes the following functions for renaming and deleting files, creating, deleting, and reading directories, and for getting information about the status of files.

Built-in Function: rename (from, to): Rename a file.

Built-in Function: unlink (file): Delete a file.

Built-in Function: readdir (dir): Returns names of files in the directory dir as an array of strings.

Built-in Function: mkdir (dir): Create a directory

Built-in Function: rmdir (dir): Remove a directory.

Built-in Function: umask (mask): Set permission mask for file creation.

Built-in Function: stat (file): Get information about a file. If file is a symbolic link, stat returns information about the file that the symbolic link references.

Built-in Function: lstat (file): Get information about a symbolic link. If file is not a symbolic link, lstat is equivalent to stat.

Built-in Function: glob (pattern): Given an array of strings in pattern, return the list of file names that any of them, or an empty string if no patterns match. Tilde expansion is performed on each of the patterns before looking for matching file names.

Built-in Function: fnmatch (pattern, string): Return 1 or zero for each element of string that matches any of the elements of the string array pattern, using the rules of filename pattern matching.

Interacting with the OS

Built-in Function: fork (): Create a copy of the current process.

Built-in Function: exec (file, args): Replace current process with a new process.

Built-in Function: fid = dup2 (old, new): Duplicate a file descriptor.

Built-in Function: [file_ids, status] = pipe (): Create an interprocess channel.

Built-in Function: fcntl (fid, request, argument)

Control open file descriptors.

F_DUPFD
F_GETFD
F_GETFL
F_SETFD
F_SETFL
O_APPEND
O_CREAT
O_EXCL
O_NONBLOCK
O_RDONLY
O_RDWR
O_TRUNC
O_WRONLY

Built-in Function: getpgrp (): Return the process group id of the current process.

Built-in Function: getpid (): Return the process id of the current process.

Built-in Function: getppid (): Return the process id of the parent process.

Built-in Function: geteuid (): Return the effective user id of the current process.

Built-in Function: getuid (): Return the real user id of the current process.

Built-in Function: getegid (): Return the effective group id of the current process.

Built-in Function: getgid (): Return the real group id of the current process.

Built-in Function: mkfifo: Create a FIFO special file.

Built-in Function: waitpid: Check the status of or wait for subprocesses.

Built-in Function: atexit (fcn): Register function to be called when Octave exits.

Built-in Function: system (string, return_output, type)

Execute a shell command specified by string. The second argument is optional. If type is "async", the process is started in the background and the process id of the child proces is returned immediately. Otherwise, the process is started, and Octave waits until it exits. If type argument is omitted, a value of "sync" is assumed.

If two input arguments are given (the actual value of return_output is irrelevant) and the subprocess is started synchronously, or if system is called with one input argument and one or more output arguments, the output from the command is returned. Otherwise, if the subprocess is executed synchronously, it's output is sent to the standard output. To send the output of a command executed with system through the pager, use a command like

disp (system (cmd, 1));

printf ("%s\n", system (cmd, 1));

The system function can return two values. The first is any output from the command that was written to the standard output stream, and the second is the output status of the command. For example,

[output, status] = system ("echo foo; exit 2");

will set the variable output to the string `foo', and the variable status to the integer `2'.

Built-in Variable: EXEC_PATH

The variable EXEC_PATH is a colon separated list of directories to search when executing subprograms. Its initial value is taken from the environment variable OCTAVE_EXEC_PATH (if it exists) or PATH, but that value can be overridden by the the command line argument --exec-path PATH, or by setting the value of EXEC_PATH in a startup script. If the value of EXEC_PATH begins (ends) with a colon, the directories

OCTAVE_HOME/libexec/octave/site/exec/ARCH
OCTAVE_HOME/libexec/octave/VERSION/exec/ARCH
OCTAVE_HOME/bin

are prepended (appended) to EXEC_PATH, where OCTAVE_HOME is the top-level directory where all of Octave is installed (`/usr/local' by default). If you don't specify a value for EXEC_PATH explicitly, these special directories are prepended to your shell path.

Built-in Function: getenv (var)

Returns the value of the environment variable var. For example,

getenv ("PATH")

returns a string containing the value of your path.

Built-in Function: putenv (var, value): Set the value of the environment variable var to value.

Built-in Function: clc ()
Built-in Function: home (): Clear the terminal screen and move the cursor to the upper left corner.

Command: cd dir

Command: chdir dir

Change the current working directory to dir. For example,

cd ~/octave

Changes the current working directory to `~/octave'. If the directory does not exist, an error message is printed and the working directory is not changed.

Built-in Function: pwd (): Returns the current working directory.

Built-in Variable: PWD: The current working directory. The value of PWD is updated each time the current working directory is changed with the `cd' command.

Command: ls

Command: dir

List directory contents. For example,

octave:13> ls -l
total 12
-rw-r--r--   1 jwe      users        4488 Aug 19 04:02 foo.m
-rw-r--r--   1 jwe      users        1315 Aug 17 23:14 bar.m

The dir and ls commands are implemented by calling your system's directory listing command, so the available options may vary from system to system.

Password Database Functions

Octave's password database functions return information in a structure with the following fields.

name: The user name.
passwd: The encrypted password, if available.
uid: The numeric user id.
gid: The numeric group id.
gecos: The GECOS field.
dir: The home directory.
shell: The initial shell.

Loadable Function: passwd_struct = getpwent (): Return an entry from the password database, opening it if necessary. Once the end of the data has been reached, getpwent returns 0.

Loadable Function: passwd_struct = getpwuid (uid).: Return the first entry from the password database with the user ID uid. If the user ID does not exist in the database, getpwuid returns 0.

Loadable Function: passwd_struct = getpwnam (name): Return the first entry from the password database with the user name name. If the user name does not exist in the database, getpwname returns 0.

Loadable Function: setpwent (): Return the internal pointer to the beginning of the password database.

Loadable Function: endpwent (): Close the password database.

Group Database Functions

Octave's group database functions return information in a structure with the following fields.

name: The user name.
passwd: The encrypted password, if available.
gid: The numeric group id.
mem: The members of the group.

Loadable Function: group_struct = getgrent (): Return an entry from the group database, opening it if necessary. Once the end of the data has been reached, getgrent returns 0.

Loadable Function: group_struct = getgrgid (gid).: Return the first entry from the group database with the group ID gid. If the group ID does not exist in the database, getgrgid returns 0.

Loadable Function: group_struct = getgrnam (name): Return the first entry from the group database with the group name name. If the group name does not exist in the database, getgrname returns 0.

Loadable Function: setgrent (): Return the internal pointer to the beginning of the group database.

Loadable Function: endgrent (): Close the group database.

System Information

Built-in Function: computer ()

Returns a string of the form cpu-vendor-os that identifies the kind of computer Octave is running on. For example,

octave:13> computer
sparc-sun-sunos4.1.2

Built-in Function: isieee (): Return 1 if your computer claims to conform to the IEEE standard for floating point calculations.

Built-in Function: version (): Returns Octave's version number as a string. This is also the value of the built-in variable OCTAVE_VERSION. See section Built-in Variables.

Loadable Function: getrusage ()

Return a structure containing a number of statistics about the current Octave process. Not all fields are available on all systems. If it is not possible to get CPU time statistics, the CPU time slots are set to zero. Other missing data are replaced by NaN. Here is a list of all the possible fields that can be present in the structure returned by getrusage:


idrss: Unshared data size.
inblock: Number of block input operations.
isrss: Unshared stack size.
ixrss: Shared memory size.
majflt: Number of major page faults.
maxrss: Maximum data size.
minflt: Number of minor page faults.
msgrcv: Number of messages received.
msgsnd: Number of messages sent.
nivcsw: Number of involuntary context switches.
nsignals: Number of signals received.
nswap: Number of swaps.
nvcsw: Number of voluntary context switches.
oublock: Number of block output operations.
stime: A structure containing the system CPU time used. The structure has the elements sec (seconds) usec (microseconds).
utime: A structure containing the user CPU time used. The structure has the elements sec (seconds) usec (microseconds).

Other Functions

Built-in Function: tilde_expand (string): Performs tilde expansion on string.

Built-in Function: pause (seconds)

Suspend the execution of the program. If invoked without any arguments, Octave waits until you type a character. With a numeric argument, it pauses for the given number of seconds. For example, the following statement prints a message and then waits 5 seconds before clearing the screen.

fprintf (stderr, "wait please...\n");
pause (5);
clc;

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