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<title>Simple interactive use</title>
<h1>2 <a name="s2"> Simple interactive use </h1>
<p> <a href="usrguide.html#toc2"> Contents of this section</a></p>
<p></p>
<p>When you start Tela from the Unix prompt without arguments (usually by
typing <b>tela</b>), the system enters interactive mode after reading
some initialization files and is ready to parse and execute command
lines. The Tela prompt is ``> ''. The GNU Readline library is the first
layer interacting with the user. This library makes it easy to modify
and reexecute previous commands. The most important key combinations
are (Ctrl means keeping Control down when pressing the key):</p>
<p>
<blockquote><code>
<pre>
Ctrl-P Get Previous line
Ctrl-N Get Next line
Ctrl-F Forward cursor one character position
Ctrl-B Backward cursor one character position
Ctrl-A Set cursor position at beginning of line
Ctrl-E Set cursor position at End of line
Ctrl-K Delete (Kill) text beyond cursor position
TAB Try to complete reserved word, identifier or filename
Enter Execute command line (cursor need not be at end position)
Ctrl-C Interrupt command during command execution
Ctrl-D Quit Tela (must be alone in line)
</pre>
</code></blockquote>
</p>
<p>You have probably used other software which also uses the GNU Readline
library, e.g. the GNU debugger <b>gdb</b>. If your terminal is properly
configured, you can use the arrow keys instead of Ctrl-P, Ctrl-N,
Ctrl-F and Ctrl-B to move in the history buffer. You should get
familiar with these commands as soon as possible, since it will
greatly speed up your working with Tela. The command completion is
able to complete Tela reserved words, function names (either
intrinsic, standard, or user-defined), variables names and
filenames. Filename completion is invoked if the TAB key is pressed
inside a string (``...''). This can be useful with the <b>source</b>
command, for example.</p>
<p>Tela uses the X window system to display graphics. The graphics is
displayed by a separate program, named PlotMTV, but calling it is
transparent to the user. The DISPLAY environment variable must be
properly defined, otherwise the graphics will not work.</p>
<p>Try entering the following commands first (``> `` means the Tela prompt
which you obviously do not type):</p>
<p>
<blockquote><code>
<pre>
> x=0:0.1:4*pi
> plot(x,sin(x))
</pre>
</code></blockquote>
</p>
<p>The first command creates a vector of real numbers ranging from 0 to 4
times Pi with step 0.1 and assigns the vector to variables x. The
second command then plots sin(x) versus x. A graph of sin(x) should
appear in a new PlotMTV window, if not, the system is not properly
installed.</p>
<p>In Matlab, an expression is printed if there is no semicolon at the
end of command line. In Tela, however, an expression is printed if it
is not assigned to any variable, regardless of any semicolon. In fact,
Tela internally inserts a semicolon at the end of every command line
before actually parsing it. The insertion is not done when reading
commands from a file.</p>
<p>This leads us to the next topic: how to execute commands from a file.
Type</p>
<p>
<blockquote><code>
<pre>
> source("demo")
</pre>
</code></blockquote>
</p>
<p>A menu of choices appears, but let us first explain what the
<b>source</b> command does. It looks for file named ``demo.t'' in the
current TELAPATH (if the file name contains a period, the ``.t'' is
not appended). The TELAPATH is a list of directories where input files
are searched, similar in function to the Unix PATH. The file
``demo.t'' is found in some standard directory and commands in it are
executed. The current TELAPATH can be seen by giving the command
<b>telapath()</b>.</p>
<p>When reading commands from a t-file, there should be a semicolon at the
end of each statement (or actually separating the consecutive
statements, but the difference is unessential here).</p>
<p>OK, now play with the demos. Press a number and ENTER to the menus, to
get back to command level select Quit.</p>
<p>The typical and recommended way to use Tela when developing something
bigger than one line is the following: Open an editor window and a
shell (Xterm) executing Tela on your workstation. Create a t-file, for
example ``mine.t'' with the editor and write some Tela commands in
it. Remember to use semicolons as statement separators. Try it out by
typing <b>source(``mine.t'')</b> in the Tela window. You must have
started Tela from the same directory where ``mine.t'' lies, or you can
use the Tela <b>cd</b> command to change to that directory. (See
<b>help cd</b>.) Doing this repeatedly you only need save the file from
the editor and press Ctrl-P ENTER in Tela window to execute the file
with changes you just made. This is only slightly clumsier than
program development with Turbo Pascal in the old times: instead of a
single keypress you now have to press three keys and switch the window with
the mouse once to execute the program!</p>
<p></p>
<p><a href="usrguide-3.html"> Next </a> Chapter, <a href="usrguide-1.html"> Previous </a> Chapter</p><p>Table of contents of <a href="usrguide.html#toc2">this chapter</a>,
General <a href="usrguide.html#toc">table of contents</a></p>
<p><a href="usrguide.html"> Top </a> of the document,
<a href="#0"> Beginning of this Chapter</a></p>
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