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<!--startcut ==========================================================-->
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<title>Xenmenu: An ASCII Menu Generator LG #39</title>
</HEAD>
<BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#0000AF"
ALINK="#FF0000">
<!--endcut ============================================================-->
<H4>
"Linux Gazette...<I>making Linux just a little more fun!</I>"
</H4>
<P> <HR> <P>
<!--===================================================================-->
<center>
<H1><font color="maroon">Xenmenu: An ASCII Menu Generator</font></H1>
<H4>By <a href="mailto:xenon@xenos.net">Karyl F. Stein</a></H4>
</center>
<P> <HR> <P>
Even though the world is moving toward slick graphical user interfaces and
World Wide Web (WWW) technology, there is still a need to cater to those who
use ASCII-based terminals. For example, many Internet Service Providers offer
shell accounts, and even more public-access systems see a lot of use of their
text-based interfaces. The systems that offer ASCII front-ends often have
programs to automate common tasks that a user would want to accomplish, but
the user still has to learn how to run those programs from a shell prompt.
Some organizations have developed complex menu systems that shield the user
from the intricacies of the underlying system. However, those programs--
usually written in some shell scripting language--are often slow, offer
minimal security, consume an inordinate amount of resources, and may be
confusing to maintain.
<P>
Having experience as an administrator for a few public-access systems, I have
been faced with the challenge of not only designing browser independent WWW
interfaces, but also easy-to-use text-based interfaces. After creating
mixtures of clunky shell scripts and inflexible C programs to address the
latter, I decided that it would make things easier for me and other
administrators to have a fast, easy-to-manage, and highly configurable method
for generating text menus. The solution that I came up with, and which I will
be discussing in this article, is Xenmenu, (pronounced zen-menu).
<P>
During the initial design of Xenmenu, a few major goals were addressed. First
and foremost, a solution that strives to make things easy should not be overly
complex to use or administrate. At the same time, this solution should be
flexible enough to allow administrators to tailor the system to meet their
exacting specifications. These requirements may include a security policy for
a site, so Xenmenu needs to incorporate features that allow it to be used as
a secure shell. Finally, Xenmenu should be as small and fast as possible.
<P>
The four main components of Xenmenu are the core program, the configuration
files, the menu description files, and the support files. The job of the core
program is to first configure itself, then go into a loop of reading the menu
description files, formating and displaying them to the user, and reading the
user's input. Each of these stages will now be described in detail.
<P>
There are three configuration files which may or may not exist. The first two
of these files are analogous to the system-wide and user-specific shell
configuration files such as /etc/csh.login and ~/.login. The final
configuration file, which also may or may not exist, is the secure
configuration file; any previous action taken by the first two configuration
files may be overridden by the secure configuration file. This allows
administrators to give users access to change their environment without
compromising security. Of course, the installer may also opt to disallow the
user from creating a personalized configuration file at all if security is a
major concern.
<P>
The configuration files only allow two directives: the setting of
environment variables and the execution of programs. For this reason the
configuration language is simple. The format of the configuration files are:
<PRE>
ENVIRONMENT_VARIABLE VALUE
run PROGRAM [ARGUMENT [ARGUMENT ...]]
</PRE>
The first line is an example of setting an environment variable. An example
of this in use would be: PAGER /usr/bin/more. This would set the environment
variable PAGER equal to /usr/bin/more. The second line is an example of
executing an external program from within the configuration file. An example
of this would be: run /bin/cat /etc/motd.
<P>
Once the configuration files are acted upon, a menu file is read and displayed
to the user. These menu files are the most important part of Xenmenu from an
administrator's standpoint since they define how the menu will look and react
to the user. Since most of an administrator's time will be spent writing the
menu files, they are designed to be easy to create. At the same time,
flexibility is a major concern.
<P>
Menu files are plain text files that may be modified and reinstalled even
while people are actively using Xenmenu. Each line of a menu file is a
command, comment, or a blank line. Commands may have zero or more arguments
separated by one or more spaces depending on the command. Comments are
inserted by placing a # as the first non-space character on a line and
continue until a new line is reached. Blank lines are ignored.
<P>
There are three main parts to a menu file: global options, formatting and
display options, and choice declarations. Global options should appear
before any choice declarations are made and affect the overall look and feel
of the menu. Currently, there are only two global options: checkcase and
nocheckcase. If checkcase is defined, then choice declarations will be
case sensitive. This means that if the user enters a "Q", it will be
acted upon differently than if they entered a "q". The default behavior is
nocheckcase which means that a user may enter either a "Q" or a "q" and the
same action will be taken.
<P>
The bulk of the commands available for use in menu files are the formatting
and display options. These options define how a menu will be drawn on a
user's screen and may be given at any point within a menu file.
The available commands and the arguments they accept, (if any), are given
below. Arguments given in <> marks are required, while those in [] marks are
optional. Some references are made to the file config.h. This file is part
of the Xenmenu distribution and may be edited before compilation when
installing Xenmenu.
<ul>
<li><font color="maroon">center <string></font>: Centers the given string on the screen. The string
will be wrapped as needed to fit on the user's
screen.
<li><font color="maroon">columns [number]</font>: Set the number of columns in which to print options
to [number]. If [number] is not defined, then 1
column is used. This is analogous to the HTML
<table> declaration.
<li><font color="maroon">header [header]</font>: Defines the menu header to be [header]. If header
is blank, then MENUHEAD as defined in config.h is
used.
<li><font color="maroon">name [name]</font>: Defines the menu name to be [name]. If [name] is
blank, then [name] is cleared.
<li><font color="maroon">notype</font>: Suppresses the printing of the option type, (i.e.
menu, file, or exit) after the option name.
<li><font color="maroon">opttail [string]</font>: Defines [string] as the string to be printed after
an option value, (it is what separates the option
value and the option name).
<li><font color="maroon">print [-n] [string]</font>: Prints [string] to the screen. If no string is
defined, a blank line will be printed. If [string]
contains something between '' marks, it is taken as a
command to be run. To print a ' character, enter it
as ''. Environment variables may be printed by
preceding them with a $ mark. To print a $
character, enter it as $$. If the -n argument is
given, than a newline is not appended to the end of
[string]. Usually, all leading spaces and tabs are
removed from [string] before it is printed to the
screen. In order to print leading spaces, begin the
string with a double quote. Any double quotes within
the string are treated as literals and printed to the
screen. A double quote found at the end of a string,
if the string begins with a double quote, is not
printed, however. A double quote may also be used if
you want to print a -n at the beginning of the string.
Finally, the string to print will be wrapped as
needed in order to fit nicely on the user's screen.
<li><font color="maroon">printfile <file></font>: Prints the <file> to the screen. If SECURE,
(defined in config.h), is > 4, then the path to
<file> is taken from SECUREDIR, otherwise <file>
should contain a path.
<li><font color="maroon">printheader</font>: Prints the menu header. The [header] will be
printed on the left side of the screen and the
[name] on the right side. A default header value,
defined in config.h is used if header is not
defined. No name is printed if not defined.
<li><font color="maroon">printline [string]</font>: Prints a line across the screen. If [string] is
not defined, a line of dashes will be printed,
otherwise a line composed of [string] will be
printed.
<li><font color="maroon">prompt [string]</font>: Sets the menu prompt to [string]. If [string] is
not defined, then DEFAULTPROMPT defined in config.h
is used. NOTE: Everything after the keyword prompt
and a space is taken as the prompt, (including
spaces).
<li><font color="maroon">run <file></font>: Runs the defined file. If SECURE, (defined in
config.h), is a 1, 3, 5, or 7, then the path to
<file> is taken from SECURERUN, otherwise <file>
should contain a path.
<li><font color="maroon">type</font>: Prints the option type, (i.e. menu, file, etc.) after
the option name. This is the default.
</ul>
Choice declarations define how the menu should react to user input. A choice
may either run an external program, display a file, load and display another
menu, or exit the menu system. Each choice may contain a value, a name, a
comment, or a combination of the three. Choices are defined in the following
way:
<PRE>
option {
<definitions>
}
</PRE>
The <definitions> part may contain one or more of the commands listed below.
The argument convention is the same as above with required arguments contained
in <> marks, and optional ones enclosed in [] marks. Again, references to
the file config.h are given.
<ul>
<li><font color="maroon">exit</font>: This means that the menu will exit if this option
is chosen.
<li><font color="maroon">file <file></font>: This is the filename that will be read if the menu
option is chosen. If SECURE, (defined in config.h),
is > 4, then the path to <file> will be taken from
SECUREDIR, otherwise <file> should contain a path.
<li><font color="maroon">menu <file>a;</font>: This means that the menu <file> will be loaded if
this option is picked. If SECURE, (defined in
config.h), is a 2, 3, 6, or 7, then the path to
<file> is taken from MENUHOME, otherwise <file>
should contain a path.
<li><font color="maroon">run <file></font>: This means that the program <file> will be run if
this option is picked. If SECURE, (defined in
config.h), is a 1, 3, 5, or 7, then the path to
<file> is taken from SECURERUN, otherwise <file>
should contain a path.
<li><font color="maroon">comment <comment></font>: This is an optional field which holds a description
of the menu item.
<li><font color="maroon">name <name></font>: This is the name of the option.
<li><font color="maroon">noprint</font>: This will cause the option not to be printed to
the screen.
<li><font color="maroon">value <value></font>: This is an optional field that holds the menu
NOTE: Values will be automatically assigned by the
menu if none is given.
</ul>
<P>
As mentioned above, Xenmenu may also be used as a secure shell. When
compiling Xenmenu, the administrator may select various security options.
Zero--the default--or more of these options may be given at compile time. The
options allow for:
<ol>
<li>The ability to only run programs in a given path,
<li>The ability to only view files under a certain directory,
<li>The ability to only view menus under a certain directory, and
<li>The ability to turn off parsing a user's personal configuration file.
</ol>
It is important to realize that Xenmenu can not make any guarantees as to the
security of any external program that it calls; if you allow the user to run
the mythical program foo from Xenmenu, and foo contains a security hole, than
the user may be able to exploit that hole to violate your security policy.
However, by using Xenmenu as a user's shell in conjunction with the above
security options, an administrator can limit what a user may do on the
system.
<P>
Finally, there are a couple small features that Xenmenu offers which are not
listed above. First of all, if the user enters something which is not an
option for the menu they are viewing, what they input is sent to a shell for
parsing. This allows the user to enter valid shell commands even if they are
not a menu option. This does not allow them to violate any security settings,
however. Secondly, the user may resize their screen and the next menu loaded
will adjust itself to fit within the new screen size.
<P>
I hope that this article gives you a good understanding of Xenmenu and what it
can do. I also hope that Xenmenu provides a solution to your need for an
ASCII menu generator, (if you have such a need). Currently, Xenmenu is still
under development, however it is actively being heavily used on more than one
system. The source code for Xenmenu is released under the Gnu Public License
and may be found at http://www.xenos.net/~xenon/software/xenmenu. The author
welcomes any suggestions, comments, or complaints you may have via E-Mail to
xenon@xenos.net.
<!--===================================================================-->
<P> <hr> <P>
<center><H5>Copyright © 1999, Karyl F. Stein <BR>
Published in Issue 39 of <i>Linux Gazette</i>, April 1999</H5></center>
<!--===================================================================-->
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