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<H1><A NAME="SEC165" HREF="octave_toc.html#TOC165">System Utilities</A></H1>

<P>
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.

</P>



<H2><A NAME="SEC166" HREF="octave_toc.html#TOC166">Timing Utilities</A></H2>

<P>
Octave's core set of functions for manipulating time values are
patterned after the corresponding functions from the standard C library.
Several of these functions use a data structure for time that includes
the following elements:

</P>
<DL COMPACT>

<DT><CODE>usec</CODE>
<DD>
Microseconds after the second (0-999999).

<DT><CODE>sec</CODE>
<DD>
Seconds after the minute (0-61).  This number can be 61 to account
for leap seconds.

<DT><CODE>min</CODE>
<DD>
Minutes after the hour (0-59).

<DT><CODE>hour</CODE>
<DD>
Hours since midnight (0-23).

<DT><CODE>mday</CODE>
<DD>
Day of the month (1-31).

<DT><CODE>mon</CODE>
<DD>
Months since January (0-11).

<DT><CODE>year</CODE>
<DD>
Years since 1900.

<DT><CODE>wday</CODE>
<DD>
Days since Sunday (0-6).

<DT><CODE>yday</CODE>
<DD>
Days since January 1 (0-365).

<DT><CODE>isdst</CODE>
<DD>
Daylight Savings Time flag.

<DT><CODE>zone</CODE>
<DD>
Time zone.
</DL>

<P>
In the descriptions of the following functions, this structure is
referred to as a <VAR>tm_struct</VAR>.

</P>
<P>
<DL>
<DT><U>Loadable Function:</U>  <B>time</B> <I>()</I>
<DD><A NAME="IDX842"></A>
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.  For example, on Monday February 17, 1997 at 07:15:06 CUT, the
value returned by <CODE>time</CODE> was 856163706.
</DL>

</P>
<P>
<DL>
<DT><U>Function File:</U>  <B>ctime</B> <I>(<VAR>t</VAR>)</I>
<DD><A NAME="IDX843"></A>
Convert a value returned from <CODE>time</CODE> (or any other nonnegative
integer), to the local time and return a string of the same form as
<CODE>asctime</CODE>.  The function <CODE>ctime (time)</CODE> is equivalent to
<CODE>asctime (localtime (time))</CODE>.  For example,

</P>

<PRE>
ctime (time ())
     => "Mon Feb 17 01:15:06 1997"
</PRE>

</DL>

<P>
<DL>
<DT><U>Loadable Function:</U>  <B>gmtime</B> <I>(<VAR>t</VAR>)</I>
<DD><A NAME="IDX844"></A>
Given a value returned from time (or any nonnegative integer),
return a time structure corresponding to CUT.  For example,

</P>

<PRE>
gmtime (time ())
     => {
           usec = 0
           year = 97
           mon = 1
           mday = 17
           sec = 6
           zone = CST
           min = 15
           wday = 1
           hour = 7
           isdst = 0
           yday = 47
         }
</PRE>

</DL>

<P>
<DL>
<DT><U>Loadable Function:</U>  <B>localtime</B> <I>(<VAR>t</VAR>)</I>
<DD><A NAME="IDX845"></A>
Given a value returned from time (or any nonnegative integer),
return a time structure corresponding to the local time zone.

</P>

<PRE>
localtime (time ())
     => {
           usec = 0
           year = 97
           mon = 1
           mday = 17
           sec = 6
           zone = CST
           min = 15
           wday = 1
           hour = 1
           isdst = 0
           yday = 47
         }
</PRE>

</DL>

<P>
<DL>
<DT><U>Loadable Function:</U>  <B>mktime</B> <I>(<VAR>tm_struct</VAR>)</I>
<DD><A NAME="IDX846"></A>
Convert a time structure corresponding to the local time to the number
of seconds since the epoch.  For example,

</P>

<PRE>
mktime (localtime (time ())
     => 856163706
</PRE>

</DL>

<P>
<DL>
<DT><U>Function File:</U>  <B>asctime</B> <I>(<VAR>tm_struct</VAR>)</I>
<DD><A NAME="IDX847"></A>
Convert a time structure to a string using the following five-field
format: Thu Mar 28 08:40:14 1996.  For example,

</P>

<PRE>
asctime (localtime (time ())
     => "Mon Feb 17 01:15:06 1997\n"
</PRE>

<P>
This is equivalent to <CODE>ctime (time ())</CODE>.
</DL>

</P>
<P>
<DL>
<DT><U>Loadable Function:</U>  <B>strftime</B> <I>(<VAR>tm_struct</VAR>)</I>
<DD><A NAME="IDX848"></A>
Format a time structure in a flexible way using <SAMP>`%'</SAMP> substitutions
similar to those in <CODE>printf</CODE>.  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 <SAMP>`%'</SAMP>
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.  For example,

</P>

<PRE>
strftime ("%r (%Z) %A %e %B %Y", localtime (time ())
     => "01:15:06 AM (CST) Monday 17 February 1997"
</PRE>

<P>
Octave's <CODE>strftime</CODE> function supports a superset of the ANSI C
field specifiers.

</P>
<P>
Literal character fields:

</P>
<DL COMPACT>

<DT><CODE>%</CODE>
<DD>
% character.

<DT><CODE>n</CODE>
<DD>
Newline character.

<DT><CODE>t</CODE>
<DD>
Tab character.
</DL>

<P>
Numeric modifiers (a nonstandard extension):

</P>
<DL COMPACT>

<DT><CODE>- (dash)</CODE>
<DD>
Do not pad the field.

<DT><CODE>_ (underscore)</CODE>
<DD>
Pad the field with spaces.
</DL>

<P>
Time fields:

</P>
<DL COMPACT>

<DT><CODE>%H</CODE>
<DD>
Hour (00-23).

<DT><CODE>%I</CODE>
<DD>
Hour (01-12).

<DT><CODE>%k</CODE>
<DD>
Hour (0-23).

<DT><CODE>%l</CODE>
<DD>
Hour (1-12).

<DT><CODE>%M</CODE>
<DD>
Minute (00-59).

<DT><CODE>%p</CODE>
<DD>
Locale's AM or PM.

<DT><CODE>%r</CODE>
<DD>
Time, 12-hour (hh:mm:ss [AP]M).

<DT><CODE>%R</CODE>
<DD>
Time, 24-hour (hh:mm).

<DT><CODE>%s</CODE>
<DD>
Time in seconds since 00:00:00, Jan 1, 1970 (a nonstandard extension).

<DT><CODE>%S</CODE>
<DD>
Second (00-61).

<DT><CODE>%T</CODE>
<DD>
Time, 24-hour (hh:mm:ss).

<DT><CODE>%X</CODE>
<DD>
Locale's time representation (%H:%M:%S).

<DT><CODE>%Z</CODE>
<DD>
Time zone (EDT), or nothing if no time zone is determinable.
</DL>

<P>
Date fields:

</P>
<DL COMPACT>

<DT><CODE>%a</CODE>
<DD>
Locale's abbreviated weekday name (Sun-Sat).

<DT><CODE>%A</CODE>
<DD>
Locale's full weekday name, variable length (Sunday-Saturday).

<DT><CODE>%b</CODE>
<DD>
Locale's abbreviated month name (Jan-Dec).

<DT><CODE>%B</CODE>
<DD>
Locale's full month name, variable length (January-December).

<DT><CODE>%c</CODE>
<DD>
Locale's date and time (Sat Nov 04 12:02:33 EST 1989).

<DT><CODE>%C</CODE>
<DD>
Century (00-99).

<DT><CODE>%d</CODE>
<DD>
Day of month (01-31).

<DT><CODE>%e</CODE>
<DD>
Day of month ( 1-31).

<DT><CODE>%D</CODE>
<DD>
Date (mm/dd/yy).

<DT><CODE>%h</CODE>
<DD>
Same as %b.

<DT><CODE>%j</CODE>
<DD>
Day of year (001-366).

<DT><CODE>%m</CODE>
<DD>
Month (01-12).

<DT><CODE>%U</CODE>
<DD>
Week number of year with Sunday as first day of week (00-53).

<DT><CODE>%w</CODE>
<DD>
Day of week (0-6).

<DT><CODE>%W</CODE>
<DD>
Week number of year with Monday as first day of week (00-53).

<DT><CODE>%x</CODE>
<DD>
Locale's date representation (mm/dd/yy).

<DT><CODE>%y</CODE>
<DD>
Last two digits of year (00-99).

<DT><CODE>%Y</CODE>
<DD>
Year (1970-).
</DL>
</DL>

<P>
Most of the remaining functions described in this section are not
patterned after the standard C library.  Some are available for
compatiblity with MATLAB and others are provided because they are
useful.

</P>
<P>
<DL>
<DT><U>Function File:</U>  <B>clock</B> <I>()</I>
<DD><A NAME="IDX849"></A>
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,

</P>

<PRE>
clock ()
     => [ 1993, 8, 20, 4, 56, 1 ]
</PRE>

<P>
The function clock is more accurate on systems that have the
<CODE>gettimeofday</CODE> function.
</DL>

</P>
<P>
<DL>
<DT><U>Function File:</U>  <B>date</B> <I>()</I>
<DD><A NAME="IDX850"></A>
Return the date as a character string in the form DD-MMM-YY.  For
example,

</P>

<PRE>
date ()
     => "20-Aug-93"
</PRE>

</DL>

<P>
<DL>
<DT><U>Function File:</U>  <B>etime</B> <I>(<VAR>t1</VAR>, <VAR>t2</VAR>)</I>
<DD><A NAME="IDX851"></A>
Return the difference (in seconds) between two time values returned from
<CODE>clock</CODE>.  For example:

</P>

<PRE>
t0 = clock ();
# many computations later...
elapsed_time = etime (clock (), t0);
</PRE>

<P>
will set the variable <CODE>elapsed_time</CODE> to the number of seconds since
the variable <CODE>t0</CODE> was set.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>total</VAR>, <VAR>user</VAR>, <VAR>system</VAR>] = <B>cputime</B> <I>();</I>
<DD><A NAME="IDX852"></A>
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, <CODE>cputime</CODE> returns 0 for each of its output values.
Note that because Octave used some CPU time to start, it is reasonable
to check to see if <CODE>cputime</CODE> works by checking to see if the total
CPU time used is nonzero.
</DL>

</P>
<P>
<DL>
<DT><U>Function File:</U>  <B>is_leap_year</B> <I>(<VAR>year</VAR>)</I>
<DD><A NAME="IDX853"></A>
Return 1 if the given year is a leap year and 0 otherwise.  If no
arguments are provided, <CODE>is_leap_year</CODE> will use the current year.
For example,

</P>

<PRE>
is_leap_year (2000)
     => 1
</PRE>

</DL>

<P>
<DL>
<DT><U>Function File:</U>  <B>tic</B> <I>()</I>
<DD><A NAME="IDX854"></A>
<DT><U>Function File:</U>  <B>toc</B> <I>()</I>
<DD><A NAME="IDX855"></A>
These functions set and check a wall-clock timer.  For example,

</P>

<PRE>
tic ();
# many computations later...
elapsed_time = toc ();
</PRE>

<P>
will set the variable <CODE>elapsed_time</CODE> to the number of seconds since
the most recent call to the function <CODE>tic</CODE>.

</P>
<P>
If you are more interested in the CPU time that your process used, you
should use the <CODE>cputime</CODE> function instead.  The <CODE>tic</CODE> and
<CODE>toc</CODE> functions report the actual wall clock time that elapsed
between the calls.  This may include time spent processing other jobs or
doing nothing at all.  For example,

</P>

<PRE>
tic (); sleep (5); toc ()
     => 5
t = cputime (); sleep (5); cputime () - t
     => 0
</PRE>

<P>
(This example also illustrates that the CPU timer may have a fairly
coarse resolution.)
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>pause</B> <I>(<VAR>seconds</VAR>)</I>
<DD><A NAME="IDX856"></A>
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.

</P>

<PRE>
fprintf (stderr, "wait please...\n");
pause (5);
clc;
</PRE>

</DL>

<P>
<DL>
<DT><U>Built-in Function:</U>  <B>sleep</B> <I>(<VAR>seconds</VAR>)</I>
<DD><A NAME="IDX857"></A>
Suspend the execution of the program for the given number of seconds.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>usleep</B> <I>(<VAR>microseconds</VAR>)</I>
<DD><A NAME="IDX858"></A>
Suspend the execution of the program for the given number of
microseconds.  On systems where it is not possible to sleep for periods
of time less than one second, <CODE>usleep</CODE> will pause the execution for
<CODE>round (<VAR>microseconds</VAR> / 1e6)</CODE> seconds.
</DL>

</P>


<H2><A NAME="SEC167" HREF="octave_toc.html#TOC167">Filesystem Utilities</A></H2>

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

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>err</VAR>, <VAR>msg</VAR>] = <B>rename</B> <I>(<VAR>old</VAR>, <VAR>new</VAR>)</I>
<DD><A NAME="IDX859"></A>
Change the name of file <VAR>old</VAR> to <VAR>new</VAR>.

</P>
<P>
If successful, <VAR>err</VAR> is 0 and <VAR>msg</VAR> is an empty string.
Otherwise, <VAR>err</VAR> is nonzero and <VAR>msg</VAR> contains a
system-dependent error message.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>err</VAR>, <VAR>msg</VAR>] = <B>unlink</B> <I>(<VAR>file</VAR>)</I>
<DD><A NAME="IDX860"></A>
Delete <VAR>file</VAR>.

</P>
<P>
If successful, <VAR>err</VAR> is 0 and <VAR>msg</VAR> is an empty string.
Otherwise, <VAR>err</VAR> is nonzero and <VAR>msg</VAR> contains a
system-dependent error message.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>files</VAR>, <VAR>err</VAR>, <VAR>msg</VAR>] = <B>readdir</B> <I>(<VAR>dir</VAR>)</I>
<DD><A NAME="IDX861"></A>
Return names of the files in the directory <VAR>dir</VAR> as an array of
strings.  If an error occurs, return an empty matrix in <VAR>files</VAR>.

</P>
<P>
If successful, <VAR>err</VAR> is 0 and <VAR>msg</VAR> is an empty string.
Otherwise, <VAR>err</VAR> is nonzero and <VAR>msg</VAR> contains a
system-dependent error message.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>err</VAR>, <VAR>msg</VAR>] = <B>mkdir</B> <I>(<VAR>dir</VAR>)</I>
<DD><A NAME="IDX862"></A>
Create a directory named <VAR>dir</VAR>.

</P>
<P>
If successful, <VAR>err</VAR> is 0 and <VAR>msg</VAR> is an empty string.
Otherwise, <VAR>err</VAR> is nonzero and <VAR>msg</VAR> contains a
system-dependent error message.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>err</VAR>, <VAR>msg</VAR>] = <B>rmdir</B> <I>(<VAR>dir</VAR>)</I>
<DD><A NAME="IDX863"></A>
Remove the directory named <VAR>dir</VAR>.

</P>
<P>
If successful, <VAR>err</VAR> is 0 and <VAR>msg</VAR> is an empty string.
Otherwise, <VAR>err</VAR> is nonzero and <VAR>msg</VAR> contains a
system-dependent error message.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>err</VAR>, <VAR>msg</VAR>] = <B>mkfifo</B> <I>(<VAR>name</VAR>)</I>
<DD><A NAME="IDX864"></A>
Create a FIFO special file.

</P>
<P>
If successful, <VAR>err</VAR> is 0 and <VAR>msg</VAR> is an empty string.
Otherwise, <VAR>err</VAR> is nonzero and <VAR>msg</VAR> contains a
system-dependent error message.
</DL>

</P>

<P>
<DL>
<DT><U>Built-in Function:</U>  <B>umask</B> <I>(<VAR>mask</VAR>)</I>
<DD><A NAME="IDX865"></A>
Set the permission mask for file creation.  The parameter <VAR>mask</VAR> is
interpreted as an octal number.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>info</VAR>, <VAR>err</VAR>, <VAR>msg</VAR>] = <B>stat</B> <I>(<VAR>file</VAR>)</I>
<DD><A NAME="IDX866"></A>
<DT><U>Built-in Function:</U> [<VAR>info</VAR>, <VAR>err</VAR>, <VAR>msg</VAR>] = <B>lstat</B> <I>(<VAR>file</VAR>)</I>
<DD><A NAME="IDX867"></A>
Return a structure <VAR>s</VAR> containing the following information about
<VAR>file</VAR>.

</P>
<DL COMPACT>

<DT><CODE>dev</CODE>
<DD>
ID of device containing a directory entry for this file.

<DT><CODE>ino</CODE>
<DD>
File number of the file.

<DT><CODE>modestr</CODE>
<DD>
File mode, as a string of ten letters or dashes as would be returned by
<KBD>ls -l</KBD>.

<DT><CODE>nlink</CODE>
<DD>
Number of links.

<DT><CODE>uid</CODE>
<DD>
User ID of file's owner.

<DT><CODE>gid</CODE>
<DD>
Group ID of file's group.

<DT><CODE>rdev</CODE>
<DD>
ID of device for block or character special files.

<DT><CODE>size</CODE>
<DD>
Size in bytes.

<DT><CODE>atime</CODE>
<DD>
Time of last access in the same form as time values returned from
<CODE>time</CODE>.  See section <A HREF="octave_30.html#SEC166">Timing Utilities</A>.

<DT><CODE>mtime</CODE>
<DD>
Time of last modification in the same form as time values returned from
<CODE>time</CODE>.  See section <A HREF="octave_30.html#SEC166">Timing Utilities</A>.

<DT><CODE>ctime</CODE>
<DD>
Time of last file status change in the same form as time values returned from
<CODE>time</CODE>.  See section <A HREF="octave_30.html#SEC166">Timing Utilities</A>.

<DT><CODE>blksize</CODE>
<DD>
Size of blocks in the file.

<DT><CODE>blocks</CODE>
<DD>
Number of blocks allocated for file.
</DL>

<P>
If the call is successful <VAR>err</VAR> is 0 and <VAR>msg</VAR> is an empty
string.  If the file does not exist, or some other error occurs, <VAR>s</VAR>
is an empty matrix, <VAR>err</VAR> is -1, and <VAR>msg</VAR> contains the
corresponding system error message.

</P>
<P>
If <VAR>file</VAR> is a symbolic link, <CODE>stat</CODE> will return information
about the actual file the is referenced by the link.  Use <CODE>lstat</CODE>
if you want information about the symbolic link itself.

</P>
<P>
For example,

</P>

<PRE>
[s, err, msg] = stat ("/vmlinuz")
     => s =
        {
          atime = 855399756
          rdev = 0
          ctime = 847219094
          uid = 0
          size = 389218
          blksize = 4096
          mtime = 847219094
          gid = 6
          nlink = 1
          blocks = 768
          modestr = -rw-r--r--
          ino = 9316
          dev = 2049
        }
     => err = 0
     => msg = 
</PRE>

</DL>

<P>
<DL>
<DT><U>Built-in Function:</U>  <B>glob</B> <I>(<VAR>pattern</VAR>)</I>
<DD><A NAME="IDX868"></A>
Given an array of strings in <VAR>pattern</VAR>, 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.  For example,

</P>

<PRE>
glob ("/vm*")
     => "/vmlinuz"
</PRE>

<P>
Note that multiple values are returned in a string matrix with the fill
character set to ASCII NUL.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>fnmatch</B> <I>(<VAR>pattern</VAR>, <VAR>string</VAR>)</I>
<DD><A NAME="IDX869"></A>
Return 1 or zero for each element of <VAR>string</VAR> that matches any of
the elements of the string array <VAR>pattern</VAR>, using the rules of
filename pattern matching.  For example,

</P>

<PRE>
fnmatch ("a*b", ["ab"; "axyzb"; "xyzab"])
     => [ 1; 1; 0 ]
</PRE>

</DL>

<P>
<DL>
<DT><U>Built-in Function:</U>  <B>file_in_path</B> <I>(<VAR>path</VAR>, <VAR>file</VAR>)</I>
<DD><A NAME="IDX870"></A>
Return the absolute name name of <VAR>file</VAR> if it can be found in
<VAR>path</VAR>.  The value of <VAR>path</VAR> should be a colon-separated list of
directories in the format described for the built-in variable
<CODE>LOADPATH</CODE>.

</P>
<P>
If the file cannot be found in the path, an empty matrix is returned.
For example,

</P>

<PRE>
file_in_path (LOADPATH, "nargchk.m")
     => "/usr/local/share/octave/2.0/m/general/nargchk.m"
</PRE>

</DL>

<P>
<DL>
<DT><U>Built-in Function:</U>  <B>tilde_expand</B> <I>(<VAR>string</VAR>)</I>
<DD><A NAME="IDX871"></A>
Performs tilde expansion on <VAR>string</VAR>.  If <VAR>string</VAR> begins with a
tilde character, (<SAMP>`~'</SAMP>), all of the characters preceding the first
slash (or all characters, if there is no slash) are treated as a
possible user name, and the tilde and the following characters up to the
slash are replaced by the home directory of the named user.  If the
tilde is followed immediately by a slash, the tilde is replaced by the
home directory of the user running Octave.  For example,

</P>

<PRE>
tilde_expand ("~joeuser/bin")
     => "/home/joeuser/bin"
tilde_expand ("~/bin")
     => "/home/jwe/bin"
</PRE>

</DL>



<H2><A NAME="SEC168" HREF="octave_toc.html#TOC168">Controlling Subprocesses</A></H2>

<P>
Octave includes some high-level commands like <CODE>system</CODE> and
<CODE>popen</CODE> for starting subprocesses.  If you want to run another
program to perform some task and then look at its output, you will
probably want to use these functions.

</P>
<P>
Octave also provides several very low-level Unix-like functions which
can also be used for starting subprocesses, but you should probably only
use them if you can't find any way to do what you need with the
higher-level functions.

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>system</B> <I>(<VAR>string</VAR>, <VAR>return_output</VAR>, <VAR>type</VAR>)</I>
<DD><A NAME="IDX872"></A>
Execute a shell command specified by <VAR>string</VAR>.  The second argument is optional.
If <VAR>type</VAR> is <CODE>"async"</CODE>, the process is started in the
background and the process id of the child process is returned
immediately.  Otherwise, the process is started, and Octave waits until
it exits.  If <VAR>type</VAR> argument is omitted, a value of <CODE>"sync"</CODE>
is assumed.

</P>
<P>
If two input arguments are given (the actual value of
<VAR>return_output</VAR> is irrelevant) and the subprocess is started
synchronously, or if <VAR>system</VAR> 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 <VAR>system</VAR> through the pager, use a command like

</P>

<PRE>
disp (system (cmd, 1));
</PRE>

<P>
or

</P>

<PRE>
printf ("%s\n", system (cmd, 1));
</PRE>

<P>
The <CODE>system</CODE> 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,

</P>

<PRE>
[output, status] = system ("echo foo; exit 2");
</PRE>

<P>
will set the variable <CODE>output</CODE> to the string <SAMP>`foo'</SAMP>, and the
variable <CODE>status</CODE> to the integer <SAMP>`2'</SAMP>.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> fid = <B>popen</B> <I>(<VAR>command</VAR>, <VAR>mode</VAR>)</I>
<DD><A NAME="IDX873"></A>
Start a process and create a pipe.  The name of the command to run is
given by <VAR>command</VAR>.  The file identifier corresponding to the input
or output stream of the process is returned in <VAR>fid</VAR>.  The argument
<VAR>mode</VAR> may be

</P>
<DL COMPACT>

<DT><CODE>"r"</CODE>
<DD>
The pipe will be connected to the standard output of the process, and
open for reading.

<DT><CODE>"w"</CODE>
<DD>
The pipe will be connected to the standard input of the process, and
open for writing.
</DL>

<P>
For example,

</P>

<PRE>
fid = popen ("ls -ltr / | tail -3", "r");
while (isstr (s = fgets (fid)))
  fputs (stdout, s);
endwhile
     -| drwxr-xr-x  33 root  root  3072 Feb 15 13:28 etc
     -| drwxr-xr-x   3 root  root  1024 Feb 15 13:28 lib
     -| drwxrwxrwt  15 root  root  2048 Feb 17 14:53 tmp
</PRE>

</DL>

<P>
<DL>
<DT><U>Built-in Function:</U>  <B>pclose</B> <I>(<VAR>fid</VAR>)</I>
<DD><A NAME="IDX874"></A>
Close a file identifier that was opened by <CODE>popen</CODE>.  You may also
use <CODE>fclose</CODE> for the same purpose.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>in</VAR>, <VAR>out</VAR>, <VAR>pid</VAR>] = <B>popen2</B> <I>(<VAR>command</VAR>, <VAR>args</VAR>)</I>
<DD><A NAME="IDX875"></A>
Start a subprocess with two-way communication.  The name of the process
is given by <VAR>command</VAR>, and <VAR>args</VAR> is an array of strings
containing options for the command.  The file identifiers for the input
and output streams of the subprocess are returned in <VAR>in</VAR> and
<VAR>out</VAR>.  If execution of the command is successful, <VAR>pid</VAR>
contains the process ID of the subprocess.  Otherwise, <VAR>pid</VAR> is
-1.

</P>
<P>
For example,

</P>

<PRE>
[in, out, pid] = popen2 ("sort", "-nr");
fputs (in, "these\nare\nsome\nstrings\n");
fclose (in);
while (isstr (s = fgets (out)))
  fputs (stdout, s);
endwhile
fclose (out);
     -| are
     -| some
     -| strings
     -| these
</PRE>

</DL>

<P>
<DL>
<DT><U>Built-in Variable:</U> <B>EXEC_PATH</B>
<DD><A NAME="IDX876"></A>
The variable <CODE>EXEC_PATH</CODE> is a colon separated list of directories
to search when executing subprograms.  Its initial value is taken from
the environment variable <CODE>OCTAVE_EXEC_PATH</CODE> (if it exists) or
<CODE>PATH</CODE>, but that value can be overridden by the command line
argument <CODE>--exec-path PATH</CODE>, or by setting the value of
<CODE>EXEC_PATH</CODE> in a startup script.  If the value of <CODE>EXEC_PATH</CODE>
begins (ends) with a colon, the directories

</P>

<PRE>
<VAR>octave-home</VAR>/libexec/octave/site/exec/<VAR>arch</VAR>
<VAR>octave-home</VAR>/libexec/octave/<VAR>version</VAR>/exec/<VAR>arch</VAR>
</PRE>

<P>
are prepended (appended) to <CODE>EXEC_PATH</CODE>, where <VAR>octave-home</VAR>
is the top-level directory where all of Octave is installed
(the default value is <TT>`/usr/local'</TT>).  If you don't specify
a value for <CODE>EXEC_PATH</CODE> explicitly, these special directories are
prepended to your shell path.
</DL>

</P>
<P>
In most cases, the following functions simply decode their arguments and
make the corresponding Unix system calls.  For a complete example of how
they can be used, look at the definition of the function <CODE>popen2</CODE>.

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>pid</VAR>, <VAR>msg</VAR>] = <B>fork</B> <I>()</I>
<DD><A NAME="IDX877"></A>
Create a copy of the current process.

</P>
<P>
Fork can return one of the following values:

</P>
<DL COMPACT>

<DT>&#62; 0
<DD>
You are in the parent process.  The value returned from <CODE>fork</CODE> is
the process id of the child process.  You should probably arrange to
wait for any child processes to exit.

<DT>0
<DD>
You are in the child process.  You can call <CODE>exec</CODE> to start another
process.  If that fails, you should probably call <CODE>exit</CODE>.

<DT>&#60; 0
<DD>
The call to <CODE>fork</CODE> failed for some reason.  You must take evasive
action.  A system dependent error message will be waiting in <VAR>msg</VAR>.
</DL>
</DL>

<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>err</VAR>, <VAR>msg</VAR>] = <B>exec</B> <I>(<VAR>file</VAR>, <VAR>args</VAR>)</I>
<DD><A NAME="IDX878"></A>
Replace current process with a new process.  Calling <CODE>exec</CODE> without
first calling <CODE>fork</CODE> will terminate your current Octave process and
replace it with the program named by <VAR>file</VAR>.  For example,

</P>

<PRE>
exec ("ls" "-l")
</PRE>

<P>
will run <CODE>ls</CODE> and return you to your shell prompt.

</P>
<P>
If successful, <CODE>exec</CODE> does not return.  If <CODE>exec</CODE> does return,
<VAR>err</VAR> will be nonzero, and <VAR>msg</VAR> will contain a system-dependent
error message.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>file_ids</VAR>, <VAR>err</VAR>, <VAR>msg</VAR>] = <B>pipe</B> <I>()</I>
<DD><A NAME="IDX879"></A>
Create a pipe and return the vector <VAR>file_ids</VAR>, which corresponding
to the reading and writing ends of the pipe.

</P>
<P>
If successful, <VAR>err</VAR> is 0 and <VAR>msg</VAR> is an empty string.
Otherwise, <VAR>err</VAR> is nonzero and <VAR>msg</VAR> contains a
system-dependent error message.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>fid</VAR>, <VAR>msg</VAR>] = <B>dup2</B> <I>(<VAR>old</VAR>, <VAR>new</VAR>)</I>
<DD><A NAME="IDX880"></A>
Duplicate a file descriptor.

</P>
<P>
If successful, <VAR>fid</VAR> is greater than zero and contains the new file
ID.  Otherwise, <VAR>fid</VAR> is negative and <VAR>msg</VAR> contains a
system-dependent error message.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>pid</VAR>, <VAR>msg</VAR>] = <B>waitpid</B> <I>(<VAR>pid</VAR>, <VAR>options</VAR>)</I>
<DD><A NAME="IDX881"></A>
Wait for process <VAR>pid</VAR> to terminate.  The <VAR>pid</VAR> argument can be:

</P>
<DL COMPACT>

<DT>-1
<DD>
Wait for any child process.

<DT>0
<DD>
Wait for any child process whose process group ID is equal to that of
the Octave interpreter process.

<DT>&#62; 0
<DD>
Wait for termination of the child process with ID <VAR>pid</VAR>.
</DL>

<P>
The <VAR>options</VAR> argument can be:

</P>
<DL COMPACT>

<DT>0
<DD>
Wait until signal is received or a child process exits (this is the
default if the <VAR>options</VAR> argument is missing).

<DT>1
<DD>
Do not hang if status is not immediately available.

<DT>2
<DD>
Report the status of any child processes that are stopped, and whose
status has not yet been reported since they stopped.

<DT>3
<DD>
Implies both 1 and 2.
</DL>

<P>
If the returned value of <VAR>pid</VAR> is greater than 0, it is the process
ID of the child process that exited.  If an error occurs, <VAR>pid</VAR> will
be less than zero and <VAR>msg</VAR> will contain a system-dependent error
message.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U> [<VAR>err</VAR>, <VAR>msg</VAR>] = <B>fcntl</B> <I>(<VAR>fid</VAR>, <VAR>request</VAR>, <VAR>arg</VAR>)</I>
<DD><A NAME="IDX882"></A>
Change the properties of the open file <VAR>fid</VAR>.  The following values
may be passed as <VAR>request</VAR>:

</P>
<DL COMPACT>

<DT><CODE>F_DUPFD</CODE>
<DD>
<A NAME="IDX883"></A>
Return a duplicate file descriptor.

<DT><CODE>F_GETFD</CODE>
<DD>
<A NAME="IDX884"></A>
Return the file descriptor flags for <VAR>fid</VAR>.

<DT><CODE>F_SETFD</CODE>
<DD>
<A NAME="IDX885"></A>
Set the file descriptor flags for <VAR>fid</VAR>.

<DT><CODE>F_GETFL</CODE>
<DD>
<A NAME="IDX886"></A>
Return the file status flags for <VAR>fid</VAR>.  The following codes may be
returned (some of the flags may be undefined on some systems).

<DL COMPACT>

<DT><CODE>O_RDONLY</CODE>
<DD>
<A NAME="IDX887"></A>
Open for reading only.

<DT><CODE>O_WRONLY</CODE>
<DD>
<A NAME="IDX888"></A>
Open for writing only.

<DT><CODE>O_RDWR</CODE>
<DD>
<A NAME="IDX889"></A>
Open for reading and writing.

<DT><CODE>O_APPEND</CODE>
<DD>
<A NAME="IDX890"></A>
Append on each write.

<DT><CODE>O_NONBLOCK</CODE>
<DD>
<A NAME="IDX891"></A>
Nonblocking mode.

<DT><CODE>O_SYNC</CODE>
<DD>
<A NAME="IDX892"></A>
Wait for writes to complete.

<DT><CODE>O_ASYNC</CODE>
<DD>
<A NAME="IDX893"></A>
Asynchronous I/O.
</DL>

<DT><CODE>F_SETFL</CODE>
<DD>
<A NAME="IDX894"></A>
Set the file status flags for <VAR>fid</VAR> to the value specified by
<VAR>arg</VAR>.  The only flags that can be changed are <CODE>O_APPEND</CODE> and
<CODE>O_NONBLOCK</CODE>.
</DL>

<P>
If successful, <VAR>err</VAR> is 0 and <VAR>msg</VAR> is an empty string.
Otherwise, <VAR>err</VAR> is nonzero and <VAR>msg</VAR> contains a
system-dependent error message.
</DL>

</P>


<H2><A NAME="SEC169" HREF="octave_toc.html#TOC169">Process, Group, and User IDs</A></H2>

<P>
<DL>
<DT><U>Built-in Function:</U>  <B>getpgrp</B> <I>()</I>
<DD><A NAME="IDX895"></A>
Return the process group id of the current process.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>getpid</B> <I>()</I>
<DD><A NAME="IDX896"></A>
Return the process id of the current process.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>getppid</B> <I>()</I>
<DD><A NAME="IDX897"></A>
Return the process id of the parent process.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>geteuid</B> <I>()</I>
<DD><A NAME="IDX898"></A>
Return the effective user id of the current process.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>getuid</B> <I>()</I>
<DD><A NAME="IDX899"></A>
Return the real user id of the current process.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>getegid</B> <I>()</I>
<DD><A NAME="IDX900"></A>
Return the effective group id of the current process.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>getgid</B> <I>()</I>
<DD><A NAME="IDX901"></A>
Return the real group id of the current process.
</DL>

</P>


<H2><A NAME="SEC170" HREF="octave_toc.html#TOC170">Environment Variables</A></H2>

<P>
<DL>
<DT><U>Built-in Function:</U>  <B>getenv</B> <I>(<VAR>var</VAR>)</I>
<DD><A NAME="IDX902"></A>
Return the value of the environment variable <VAR>var</VAR>.  For example,

</P>

<PRE>
getenv ("PATH")
</PRE>

<P>
returns a string containing the value of your path.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>putenv</B> <I>(<VAR>var</VAR>, <VAR>value</VAR>)</I>
<DD><A NAME="IDX903"></A>
Set the value of the environment variable <VAR>var</VAR> to <VAR>value</VAR>.
</DL>

</P>


<H2><A NAME="SEC171" HREF="octave_toc.html#TOC171">Current Working Directory</A></H2>

<P>
<DL>
<DT><U>Command:</U> <B>cd</B> <I>dir</I>
<DD><A NAME="IDX904"></A>
<DT><U>Command:</U> <B>chdir</B> <I>dir</I>
<DD><A NAME="IDX905"></A>
Change the current working directory to <VAR>dir</VAR>.  For example,

</P>

<PRE>
cd ~/octave
</PRE>

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

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>pwd</B> <I>()</I>
<DD><A NAME="IDX906"></A>
Return the current working directory.
</DL>

</P>
<P>
<DL>
<DT><U>Command:</U> <B>ls</B> <I>options</I>
<DD><A NAME="IDX907"></A>
<DT><U>Command:</U> <B>dir</B> <I>options</I>
<DD><A NAME="IDX908"></A>
List directory contents.  For example,

</P>

<PRE>
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
</PRE>

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

</P>


<H2><A NAME="SEC172" HREF="octave_toc.html#TOC172">Password Database Functions</A></H2>

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

</P>
<DL COMPACT>

<DT><CODE>name</CODE>
<DD>
The user name.

<DT><CODE>passwd</CODE>
<DD>
The encrypted password, if available.

<DT><CODE>uid</CODE>
<DD>
The numeric user id.

<DT><CODE>gid</CODE>
<DD>
The numeric group id.

<DT><CODE>gecos</CODE>
<DD>
The GECOS field.

<DT><CODE>dir</CODE>
<DD>
The home directory.

<DT><CODE>shell</CODE>
<DD>
The initial shell.
</DL>

<P>
In the descriptions of the following functions, this data structure is
referred to as a <VAR>pw_struct</VAR>.

</P>
<P>
<DL>
<DT><U>Loadable Function:</U> <VAR>pw_struct</VAR> =  <B>getpwent</B> <I>()</I>
<DD><A NAME="IDX909"></A>
Return a structure containing an entry from the password database,
opening it if necessary. Once the end of the data has been reached,
<CODE>getpwent</CODE> returns 0.
</DL>

</P>
<P>
<DL>
<DT><U>Loadable Function:</U> <VAR>pw_struct</VAR> =  <B>getpwuid</B> <I>(<VAR>uid</VAR>).</I>
<DD><A NAME="IDX910"></A>
Return a structure containing the first entry from the password database
with the user ID <VAR>uid</VAR>.  If the user ID does not exist in the
database, <CODE>getpwuid</CODE> returns 0.
</DL>

</P>
<P>
<DL>
<DT><U>Loadable Function:</U> <VAR>pw_struct</VAR> =  <B>getpwnam</B> <I>(<VAR>name</VAR>)</I>
<DD><A NAME="IDX911"></A>
Return a structure containing the first entry from the password database
with the user name <VAR>name</VAR>.  If the user name does not exist in the
database, <CODE>getpwname</CODE> returns 0.
</DL>

</P>
<P>
<DL>
<DT><U>Loadable Function:</U>  <B>setpwent</B> <I>()</I>
<DD><A NAME="IDX912"></A>
Return the internal pointer to the beginning of the password database.
</DL>

</P>
<P>
<DL>
<DT><U>Loadable Function:</U>  <B>endpwent</B> <I>()</I>
<DD><A NAME="IDX913"></A>
Close the password database.
</DL>

</P>


<H2><A NAME="SEC173" HREF="octave_toc.html#TOC173">Group Database Functions</A></H2>

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

</P>
<DL COMPACT>

<DT><CODE>name</CODE>
<DD>
The user name.

<DT><CODE>passwd</CODE>
<DD>
The encrypted password, if available.

<DT><CODE>gid</CODE>
<DD>
The numeric group id.

<DT><CODE>mem</CODE>
<DD>
The members of the group.
</DL>

<P>
In the descriptions of the following functions, this data structure is
referred to as a <VAR>grp_struct</VAR>.

</P>
<P>
<DL>
<DT><U>Loadable Function:</U> <VAR>grp_struct</VAR> = <B>getgrent</B> <I>()</I>
<DD><A NAME="IDX914"></A>
Return an entry from the group database, opening it if necessary.
Once the end of the data has been reached, <CODE>getgrent</CODE> returns 0.
</DL>

</P>
<P>
<DL>
<DT><U>Loadable Function:</U> <VAR>grp_struct</VAR> = <B>getgrgid</B> <I>(<VAR>gid</VAR>).</I>
<DD><A NAME="IDX915"></A>
Return the first entry from the group database with the group ID
<VAR>gid</VAR>.  If the group ID does not exist in the database,
<CODE>getgrgid</CODE> returns 0.
</DL>

</P>
<P>
<DL>
<DT><U>Loadable Function:</U> <VAR>grp_struct</VAR> = <B>getgrnam</B> <I>(<VAR>name</VAR>)</I>
<DD><A NAME="IDX916"></A>
Return the first entry from the group database with the group name
<VAR>name</VAR>.  If the group name does not exist in the database,
<CODE>getgrname</CODE> returns 0.
</DL>

</P>
<P>
<DL>
<DT><U>Loadable Function:</U>  <B>setgrent</B> <I>()</I>
<DD><A NAME="IDX917"></A>
Return the internal pointer to the beginning of the group database.
</DL>

</P>
<P>
<DL>
<DT><U>Loadable Function:</U>  <B>endgrent</B> <I>()</I>
<DD><A NAME="IDX918"></A>
Close the group database.
</DL>

</P>


<H2><A NAME="SEC174" HREF="octave_toc.html#TOC174">System Information</A></H2>

<P>
<DL>
<DT><U>Built-in Function:</U>  <B>computer</B> <I>()</I>
<DD><A NAME="IDX919"></A>
Print or return a string of the form <VAR>cpu</VAR>-<VAR>vendor</VAR>-<VAR>os</VAR>
that identifies the kind of computer Octave is running on.  If invoked
with an output argument, the value is returned instead of printed.  For
example,

</P>

<PRE>
computer ()
     -| i586-pc-linux-gnu

x = computer ()
     => x = "i586-pc-linux-gnu"
</PRE>

</DL>

<P>
<DL>
<DT><U>Built-in Function:</U>  <B>isieee</B> <I>()</I>
<DD><A NAME="IDX920"></A>
Return 1 if your computer claims to conform to the IEEE standard for
floating point calculations.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>version</B> <I>()</I>
<DD><A NAME="IDX921"></A>
Return Octave's version number as a string.  This is also the value of
the built-in variable <CODE>OCTAVE_VERSION</CODE>.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Variable:</U> <B>OCTAVE_VERSION</B>
<DD><A NAME="IDX922"></A>
The version number of Octave, as a string.
</DL>

</P>
<P>
<DL>
<DT><U>Built-in Function:</U>  <B>octave_config_info</B> <I>()</I>
<DD><A NAME="IDX923"></A>
Return a structure containing configuration and installation
information.
</DL>

</P>
<P>
<DL>
<DT><U>Loadable Function:</U>  <B>getrusage</B> <I>()</I>
<DD><A NAME="IDX924"></A>
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
<CODE>getrusage</CODE>:

</P>
<DL COMPACT>

<DT><CODE></CODE>
<DD>
<DT><CODE>idrss</CODE>
<DD>
Unshared data size.

<DT><CODE>inblock</CODE>
<DD>
Number of block input operations.

<DT><CODE>isrss</CODE>
<DD>
Unshared stack size.

<DT><CODE>ixrss</CODE>
<DD>
Shared memory size.

<DT><CODE>majflt</CODE>
<DD>
Number of major page faults.

<DT><CODE>maxrss</CODE>
<DD>
Maximum data size.

<DT><CODE>minflt</CODE>
<DD>
Number of minor page faults.

<DT><CODE>msgrcv</CODE>
<DD>
Number of messages received.

<DT><CODE>msgsnd</CODE>
<DD>
Number of messages sent.

<DT><CODE>nivcsw</CODE>
<DD>
Number of involuntary context switches.

<DT><CODE>nsignals</CODE>
<DD>
Number of signals received.

<DT><CODE>nswap</CODE>
<DD>
Number of swaps.

<DT><CODE>nvcsw</CODE>
<DD>
Number of voluntary context switches.

<DT><CODE>oublock</CODE>
<DD>
Number of block output operations.

<DT><CODE>stime</CODE>
<DD>
A structure containing the system CPU time used.  The structure has the
elements <CODE>sec</CODE> (seconds) <CODE>usec</CODE> (microseconds).

<DT><CODE>utime</CODE>
<DD>
A structure containing the user CPU time used.  The structure has the
elements <CODE>sec</CODE> (seconds) <CODE>usec</CODE> (microseconds).
</DL>
</DL>

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