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Chapters:
</br>
<a href="Introduction.html">1: Introduction</a><br>
<a href="SimpleExample.html">2: Simple example</a><br>
<a href="InvokingGri.html">3: Invocation</a><br>
<a href="GettingMoreControl.html">4: Finer Control</a><br>
<a href="X-Y.html">5: X-Y Plots</a><br>
<a href="ContourPlots.html">6: Contour Plots</a><br>
<a href="Images.html">7: Image Plots</a><br>
<a href="Examples.html">8: Examples</a><br>
<a href="Commands.html">9: Gri Commands</a><br>
<a href="Programming.html">10: Programming</a><br>
<a href="Environment.html">11: Environment</a><br>
<a href="Emacs.html">12: Emacs Mode</a><br>
<a href="History.html">13: History</a><br>
<a href="Installation.html">14: Installation</a><br>
<a href="Bugs.html">15: Gri Bugs</a><br>
<a href="TestSuite.html">16: Test Suite</a><br>
<a href="Acknowledgments.html">17: Acknowledgments</a><br>
<a href="License.html">18: License</a><br>
<br>
Indices:</br>
<a href="ConceptIndex.html"><i>Concepts</i></a><br>
<a href="CommandIndex.html"><i>Commands</i></a><br>
<a href="BuiltinIndex.html"><i>Variables</i></a><br>
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<h2>10.16: Interaction Between Gri and Operating System</h2>
<UL>
<LI><a href="OperatingSystem.html#UsingOSInsideGri">Using OS Inside Gri</a>: Accessing the OS from inside Gri
<LI><a href="OperatingSystem.html#UsingGriInsideOS">Using Gri Inside OS</a>: Tricks for using Gri in unix
</UL>
<!-- @node Using OS Inside Gri, Using Gri Inside OS, Operating System, Operating System -->
<a name="UsingOSInsideGri" ></a>
<h3>10.16.1: Using the OS from within Gri</h3>
Gri uses the operating system internally for things like paging through
help information.
<p>
The operating system may be called <b>within</b> Gri commands, using a
syntax borrowed from the `<font color="#82140F"><code>Bash</code></font>' unix shell. After substituting
synonyms in the commandline, Gri scans for dollar-parenthesis blocks
(e.g. `<font color="#82140F"><code>\$(system-command)</code></font>', replacing them with the textual result
of sending the indicated system-command to the OS. The replacements are
done from left to right in the commandline, starting at the deepest
nesting level.
<p>
Often the dollar-parentheis syntax is used in title commands, to
indicate the full pathname of the Gri commandfile, e.g.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
draw title "\$(pwd)/\.command_file."
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
In assignment to synonyms, expansion of dollar-parenthesis is not done.
Thus the operating system is called twice on the second line below, and
not at all on the first line; to see this, run it as `<font color="#82140F"><code>gri -s8 -t</code></font>'.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
\dir = "\$(echo $MY_DIR)"
show "\$(head -1 \dir/MY_FILE)"
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
<b>Syntax Note</b> Dollar-parenthesis blocks must be prefixed with
backslash to avoid confusion with math expressions within strings, for
example to avoid breaking `<font color="#82140F"><code>draw label "$(x,y)$" at 3 3 cm</code></font>'. This
is an example of how TeX notation and unix shell notation collide.
<p>
<b>Example</b> It is a good idea to employ unix environment variables to name
directories containing data, so that Gri scripts will work unchanged
even if the data are moved (so long as the environment variables are
altered), e.g.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
# Figure how many lines in a file
\dir ="$(echo DIRECTORY_WHERE_I_STORE_SOLAR_DATA)"
open "\dir/solar_data_file_name`
...
open "\$(echo DIR_ANOTHER)/another_data_set"
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
Another method is to pass instructions to the operating system with the
`<font color="#82140F"><code>system</code></font>' command. This discards output. Whatever follows the word
`<font color="#82140F"><code>system</code></font>' is first scanned for synonyms (but not rpn expressions or
variables); after replacement of any existing synonyms, the line is
passed directly to the operating system. Any results are printed on the
terminal.
<p>
Frequently used system commands are `<font color="#82140F"><code>awk</code></font>', `<font color="#82140F"><code>head</code></font>', `<font color="#82140F"><code>grep</code></font>' and
`<font color="#82140F"><code>sed</code></font>'. Examples:
<p>
<ul>
<li>
Here's how to paste several files together to form a temporary file for
plotting. (Notice that a temporary file incorporating the PID of the job
is created and later removed.)
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
system paste -d" " 1.dat 2.dat 3.dat > tmp.\.pid.
open tmp.\.pid.
read columns x y
close
system rm tmp.\.pid.
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
<li>
Here's how to plot each line in a file called `<font color="#82140F"><samp>inp</samp></font>' which has
the string `<font color="#82140F"><code>;</code></font>' at the start of the line.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
system cat inp | grep -v "^;" | cat > tmp.\.pid.
open tmp.\.pid.
read columns x y
system rm tmp.\.pid.
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
<li>
Here's how to use the `<font color="#82140F"><code>awk</code></font>' system command to create a tabulated
function for plotting.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
system awk \
'BEGIN { \
for (x=0; x<1; x+=0.1) { \
printf ("%f %f\n", x, sin(x)) \
} \
}' \
> tmp.\.pid.
open tmp.\.pid.
read columns x y
close
system rm tmp.\.pid.
draw curve
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
This example is more cleanly written using the piping facility of the
`<font color="#82140F"><code>open</code></font>' command (which automatically creates a temporary file, and
destroys it when `<font color="#82140F"><code>close</code></font>' is done)
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
open "awk 'BEGIN { \
for(x=0;x<1;x+=0.1) { \
print(x,sin(x)) \
} \
}'|"
read columns x y
close
draw curve
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
<li> Sometimes you need just a single output item from the operating
system. In this case, you can store the results from the operating
system in a synonym by using the `<font color="#82140F"><code>\synonym = system ...</code></font>'
assignment command.
<li>
subroutine A related command is `<font color="#82140F"><code>\synonym = tmpname</code></font>', which
stores in the synonym the name of a temporary file created by the
system. The file is created with the `<font color="#82140F"><code>tmpname</code></font>' system call, so
it is guaranteed not to clash with any existing files. Typically, the
filename is something like `<font color="#82140F"><samp>/usr/tmp/griAAAa1233</samp></font>'. In many cases
you'll want to remove the file within Gri, once you're done, and that
can be done with `<font color="82140F"><code>unlink</code></font>' (see <a href="Unlink.html#Unlink">Unlink</a>) or with a
`<font color="#82140F"><code>system rm -f</code></font>' command. A useful bit of code is as follows
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
\file = tmpname
system ... SOME_SYSTEM_COMMANDS ... > \file
... use this new file for something ...
unlink \file
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
</ul>
<p>
<!-- @node Using Gri Inside OS, Resource File, Using OS Inside Gri, Operating System -->
<a name="UsingGriInsideOS" ></a>
<h3>10.16.2: Using Gri from within the OS</h3>
<b>This section only applies to unix systems.</b>
<p>
Save the following into a file called `<font color="#82140F"><samp>p</samp></font>' and then make it
executable using `<font color="#82140F"><code>chmod</code></font>'. It runs Gri on a named file, with the
`<font color="#82140F"><code>-yes</code></font>' flag set
so that any `<font color="#82140F"><code>query</code></font>' commands are automatically answered in the
affirmative, and then displays the results in a Ghostscript window.
(USAGE: `<font color="#82140F"><code>p cmdfile.gri</code></font>')
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
#!/usr/bin/sh
# Run Gri, then plot in gs window
case $# in
1)
base=`basename $1 .gri | sed -e s/.*,#`
gri -yes $base.gri && ghostview $base.ps
;;
*)
echo "Proper usage: $0 cmdfile.gri"
;;
esac
</font></PRE>
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