@c Copyright (C) 1996-2019 John W. Eaton
@c
@c This file is part of Octave.
@c
@c Octave is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c
@c Octave is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
@c GNU General Public License for more details.
@c
@c You should have received a copy of the GNU General Public License
@c along with Octave; see the file COPYING.  If not, see
@c <https://www.gnu.org/licenses/>.

@node System Utilities
@chapter 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.

@menu
* Timing Utilities::
* Filesystem Utilities::
* File Archiving Utilities::
* Networking Utilities::
* Controlling Subprocesses::
* Process ID Information::
* Environment Variables::
* Current Working Directory::
* Password Database Functions::
* Group Database Functions::
* System Information::
* Hashing Functions::
@end menu

@node Timing Utilities
@section Timing Utilities

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:

@table @code
@item usec
Microseconds after the second (0-999999).

@item sec
Seconds after the minute (0-60).  This number can be 60 to account
for leap seconds.

@item min
Minutes after the hour (0-59).

@item hour
Hours since midnight (0-23).

@item mday
Day of the month (1-31).

@item mon
Months since January (0-11).

@item year
Years since 1900.

@item wday
Days since Sunday (0-6).

@item yday
Days since January 1 (0-365).

@item isdst
Daylight saving time flag.

@item gmtoff
Seconds offset from UTC.

@item zone
Time zone.
@end table

@noindent
In the descriptions of the following functions, this structure is
referred to as a @var{tm_struct}.

@DOCSTRING(time)

@DOCSTRING(now)

@DOCSTRING(ctime)

@DOCSTRING(gmtime)

@DOCSTRING(localtime)

@DOCSTRING(mktime)

@DOCSTRING(asctime)

@DOCSTRING(strftime)

@DOCSTRING(strptime)

Most of the remaining functions described in this section are not
patterned after the standard C library.  Some are available for
compatibility with @sc{matlab} and others are provided because they are
useful.

@DOCSTRING(clock)

@DOCSTRING(date)

@DOCSTRING(etime)

@DOCSTRING(cputime)

@DOCSTRING(is_leap_year)

@DOCSTRING(tic)

@DOCSTRING(toc)

@DOCSTRING(pause)

@DOCSTRING(datenum)

@DOCSTRING(datestr)

@DOCSTRING(datevec)

@DOCSTRING(addtodate)

@DOCSTRING(calendar)

@DOCSTRING(weekday)

@DOCSTRING(eomday)

@DOCSTRING(datetick)

@node Filesystem Utilities
@section Filesystem Utilities

Octave includes many utility functions for copying, moving, renaming, and
deleting files; for creating, reading, and deleting directories; for retrieving
status information on files; and for manipulating file and path names.

@DOCSTRING(movefile)

@DOCSTRING(rename)

@DOCSTRING(copyfile)

@DOCSTRING(unlink)

@DOCSTRING(link)

@DOCSTRING(symlink)

@DOCSTRING(readlink)

@DOCSTRING(mkdir)

@DOCSTRING(rmdir)

@DOCSTRING(confirm_recursive_rmdir)

@DOCSTRING(mkfifo)

@DOCSTRING(umask)

@anchor{XREFlstat}
@DOCSTRING(stat)

@DOCSTRING(S_ISBLK)

@DOCSTRING(S_ISCHR)

@DOCSTRING(S_ISDIR)

@DOCSTRING(S_ISFIFO)

@DOCSTRING(S_ISLNK)

@DOCSTRING(S_ISREG)

@DOCSTRING(S_ISSOCK)

@DOCSTRING(fileattrib)

@DOCSTRING(isfile)

@DOCSTRING(isdir)

@DOCSTRING(isfolder)

@DOCSTRING(readdir)

@DOCSTRING(glob)

@DOCSTRING(file_in_path)

@DOCSTRING(filesep)

@DOCSTRING(fileparts)

@DOCSTRING(fullfile)

@DOCSTRING(tilde_expand)

@DOCSTRING(canonicalize_file_name)

@DOCSTRING(make_absolute_filename)

@DOCSTRING(is_absolute_filename)

@DOCSTRING(is_rooted_relative_filename)

@DOCSTRING(recycle)

@node File Archiving Utilities
@section File Archiving Utilities

@DOCSTRING(bunzip2)

@DOCSTRING(gzip)

@DOCSTRING(gunzip)

@DOCSTRING(tar)

@DOCSTRING(untar)

@DOCSTRING(zip)

@DOCSTRING(unzip)

@DOCSTRING(unpack)

@DOCSTRING(bzip2)

@node Networking Utilities
@section Networking Utilities

@menu
* FTP Objects::
* URL Manipulation::
* Base64 and Binary Data Transmission::
@end menu

@DOCSTRING(gethostname)

@node FTP Objects
@subsection FTP Objects

Octave supports the FTP protocol through an object-oriented interface.
Use the function @code{ftp} to create an FTP object which represents the
connection.  All FTP functions take an FTP object as the first argument.

@DOCSTRING(@ftp/ftp)

@DOCSTRING(@ftp/close)

@DOCSTRING(@ftp/mget)

@DOCSTRING(@ftp/mput)

@DOCSTRING(@ftp/cd)

@DOCSTRING(@ftp/dir)

@DOCSTRING(@ftp/ascii)

@DOCSTRING(@ftp/binary)

@DOCSTRING(@ftp/delete)

@DOCSTRING(@ftp/rename)

@DOCSTRING(@ftp/mkdir)

@DOCSTRING(@ftp/rmdir)

@node URL Manipulation
@subsection URL Manipulation

@DOCSTRING(urlread)

@DOCSTRING(urlwrite)

@node Base64 and Binary Data Transmission
@subsection Base64 and Binary Data Transmission

Some transmission channels can not accept binary data.  It is customary to
encode binary data in Base64 for transmission and to decode the data upon
reception.

@DOCSTRING(base64_encode)

@DOCSTRING(base64_decode)

@node Controlling Subprocesses
@section Controlling Subprocesses

Octave includes some high-level commands like @code{system} and
@code{popen} 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.

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.

@DOCSTRING(system)

@DOCSTRING(unix)

@DOCSTRING(dos)

@DOCSTRING(open)

@DOCSTRING(perl)

@DOCSTRING(python)

@DOCSTRING(popen)

@DOCSTRING(pclose)

@DOCSTRING(popen2)

@DOCSTRING(EXEC_PATH)

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}.

@DOCSTRING(fork)

@DOCSTRING(exec)

@DOCSTRING(pipe)

@DOCSTRING(dup2)

@DOCSTRING(waitpid)

@DOCSTRING(WCONTINUE)

@DOCSTRING(WCOREDUMP)

@DOCSTRING(WEXITSTATUS)

@DOCSTRING(WIFCONTINUED)

@DOCSTRING(WIFSIGNALED)

@DOCSTRING(WIFSTOPPED)

@DOCSTRING(WIFEXITED)

@DOCSTRING(WNOHANG)

@DOCSTRING(WSTOPSIG)

@DOCSTRING(WTERMSIG)

@DOCSTRING(WUNTRACED)

@DOCSTRING(fcntl)

@DOCSTRING(kill)

@DOCSTRING(SIG)

@node Process ID Information
@section Process, Group, and User IDs

@DOCSTRING(getpgrp)

@DOCSTRING(getpid)

@DOCSTRING(getppid)

@DOCSTRING(geteuid)

@DOCSTRING(getuid)

@DOCSTRING(getegid)

@DOCSTRING(getgid)

@node Environment Variables
@section Environment Variables

@DOCSTRING(getenv)

@DOCSTRING(setenv)

@DOCSTRING(unsetenv)

@DOCSTRING(get_home_directory)

@node Current Working Directory
@section Current Working Directory

@DOCSTRING(cd)

@DOCSTRING(ls)

@DOCSTRING(ls_command)

@DOCSTRING(dir)

@DOCSTRING(pwd)

@node Password Database Functions
@section Password Database Functions

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

@table @code
@item name
The user name.

@item passwd
The encrypted password, if available.

@item uid
The numeric user id.

@item gid
The numeric group id.

@item gecos
The GECOS field.

@item dir
The home directory.

@item shell
The initial shell.
@end table

In the descriptions of the following functions, this data structure is
referred to as a @var{pw_struct}.

@DOCSTRING(getpwent)

@DOCSTRING(getpwuid)

@DOCSTRING(getpwnam)

@DOCSTRING(setpwent)

@DOCSTRING(endpwent)

@node Group Database Functions
@section Group Database Functions

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

@table @code
@item name
The user name.

@item passwd
The encrypted password, if available.

@item gid
The numeric group id.

@item mem
The members of the group.
@end table

In the descriptions of the following functions, this data structure is
referred to as a @var{grp_struct}.

@DOCSTRING(getgrent)

@DOCSTRING(getgrgid)

@DOCSTRING(getgrnam)

@DOCSTRING(setgrent)

@DOCSTRING(endgrent)

@node System Information
@section System Information

@DOCSTRING(computer)

@DOCSTRING(uname)

@DOCSTRING(nproc)

@DOCSTRING(ispc)

@DOCSTRING(isunix)

@DOCSTRING(ismac)

@DOCSTRING(isieee)

@DOCSTRING(isdeployed)

@DOCSTRING(isstudent)

@DOCSTRING(OCTAVE_HOME)

@DOCSTRING(OCTAVE_EXEC_HOME)

@DOCSTRING(matlabroot)

@DOCSTRING(OCTAVE_VERSION)

@DOCSTRING(version)

@DOCSTRING(ver)

@DOCSTRING(compare_versions)

@DOCSTRING(license)

@DOCSTRING(getrusage)

@DOCSTRING(winqueryreg)

@node Hashing Functions
@section Hashing Functions

It is often necessary to find if two strings or files are identical.
This might be done by comparing them character by character and looking
for differences.  However, this can be slow, and so comparing a hash of
the string or file can be a rapid way of finding if the files differ.

Another use of the hashing function is to check for file integrity.  The
user can check the hash of the file against a known value and find if
the file they have is the same as the one that the original hash was
produced with.

Octave supplies the @code{hash} function to calculate hash values of
strings and files, the latter in combination with the @code{fileread}
function.  The @code{hash} function supports the most common used
cryptographic hash functions, namely MD5 and SHA-1.

@DOCSTRING(hash)
