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<br>
Chapters:
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<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>
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Indices:<br>
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<h3>9.3.50: `<font color="#82140F"><code>system</code></font>'</h3>
<!-- latex: \index{system} -->
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
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<PRE>
<font color="#82140F">
`system \system-command'
</font></PRE>
</TD>
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</TABLE>
<p>
Tell the operating system to perform the indicated action. Whatever
string follows the word `<font color="#82140F"><code>system</code></font>' is passed directly to the
operating system, <b>after</b> substitution of synonyms if any exist.
<p>
If your system command contains double-slashes, you must protect them
from Gri (which will interpret them as comments) by enclosing in
double-quotes, e.g. `<font color="#82140F"><code>system cat A | sed -e "s/foo//g" | cat > B</code></font>'.
(In the particular case of the `<font color="#82140F"><code>sed</code></font>' command you could also do
`<font color="#82140F"><code>system cat A | sed -e "s:foo::g" | cat > B</code></font>'.
<p>
Note that `<font color="#82140F"><code>rpn</code></font>' expressions are not evaluated, and variable values
are not substituted before passing the string to the operating system.
The exit status is stored in the builtin variable
`<font color="#82140F"><code>..exit_status..</code></font>'.
<p>
There are two ways to use the system:
<ul>
<li>
<b>Assign output to synonym</b>: The form `<font color="#82140F"><code>\synonym = system ...</code></font>'
does the system command and then inserts the output from that command
into the indicated synonym.)
<p>
<li> <b>Just run a command</b>: The command `<font color="#82140F"><code>system ls</code></font>' will list
the files in the current directory.
</ul>
<p>
For long commands, there are two approaches, the second preferred:
<ul>
<li>
<b>Use continuation lines</b>: String a lot of information onto one
effective system line, using the `<font color="#82140F"><code>\</code></font>' line-continuation character
at the ends of lines. The problem is that it is very easy to lose one of
these backslashes. The next method is better.
<li>
<b>Here-is syntax</b> The here-is syntax of many unix shells is also
provided. If the system command contains the characters `<font color="#82140F"><code><<</code></font>'
followed by a word (with no space between!) then Gri will issue a system
command which includes not only this line but also all succeeding lines,
until a line is found which matches the indicated word precisely (with
no leading space allowed). The `<font color="#82140F"><code><< "WORD"</code></font>' syntax is also
supported, meaning that the operating system is being told not to mess
with the dollar-signs -- needed in perl.
<p>
Be careful using this inside a new-command. Gri
Recognizes the end of the body of a new-command by a line with `<font color="#82140F"><code>}</code></font>'
in the <b>first column</b>, and no non-white characters thereafter.
If you system command happens to use a line with a curly brace (as in a
loop in perl, for example), you must put whitespace before the brace.
This won't affect the system command, but it will let Gri correctly
realize that this is <b>not</b> the end of the new-command. For more
information on new-commands (see <a href="ParsingSynonyms.html#Parsing">Parsing</a>).
<p>
<b>Caution:</b> Before sending the string to the system, Gri first
translates any synonyms present. Be careful with this, since system
commands calling awk, etc, very often use backslashes for the newline
character `<font color="#82140F"><code>\n</code></font>' within strings. If you have a synonym whose name
starts with `<font color="#82140F"><code>\n</code></font>', you can get a conflict. For example, the awk
command `<font color="#82140F"><code>print "foo\nbar";</code></font>' should print a line with `<font color="#82140F"><code>foo</code></font>' on
it, followed by a line with `<font color="#82140F"><code>bar</code></font>' on it, but it will instead print
a single line with `<font color="#82140F"><code>fooMISTAKE</code></font>', if you had previously defined a
synonym as `<font color="#82140F"><code>\nbar = "MISTAKE"</code></font>'. One way to avoid this mistake is
to make sure any `<font color="#82140F"><code>\n</code></font>' characters appear at the end of strings, and
then simply avoid having a synonym named `<font color="#82140F"><code>\n</code></font>'.
<p>
Here is a Perl example.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
\m = "Foo bar"
system perl <<"EOF"
$a = 100;
print "foo bar is \m, and a is $a\n";
print "BETTER: foo bar is \m, and a is $a\n";
print "Q: was a 100?\n";
EOF
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
</ul>
<p>
<b>Some more examples</b>:
<ul>
<li>
To get the first 15 lines of a file called `<font color="#82140F"><samp>foo.dat</samp></font>' inserted into
another file called `<font color="#82140F"><samp>bar.dat</samp></font>', you might do the following. Only
the first method works; the second will fail because `<font color="#82140F"><code>.n.</code></font>' will not
be translated before passing to the operating system.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
\num = "-15"
system head \num foo.dat > bar.dat
# Following will not work correctly because .num.
# will not be translated
.num. = -15
system head .num. foo.dat > bar.dat
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
<li>
Issue a unix command to get a listing of files in the current
working directory, and pipe them into the `<font color="#82140F"><code>more</code></font>' system command.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
system ls -l *c | more
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
<li>
Store the date and time into a synonym, and use it in a
title:
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
\time = system date
...
draw title "Plotted at time \time"
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
<li>
Use `<font color="#82140F"><code>awk</code></font>' to prepare a two-column table of x, ranging
from 0 to 1 in steps of 0.1, and sin(x). The table is stored in a file
whose suffix is the process ID of the Gri job. This file is then
opened, and the data plotted. Finally, a system command is issued to
remove the temporary file.
<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>
<b>Note</b>: in unix, this command calls the Bourne shell, not the C-shell
that is often used interactively. For many simple uses, the only
difference from normal interactive use will be that `<font color="#82140F"><code>~</code></font>' is not
expanded to the home directory. For example, you should write
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
system awk -f $HOME/foo/bar/cmd.gawk
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
instead of the
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
system awk -f ~/foo/bar/cmd.gawk
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
that you might expect from interactive C-shell use.
<p>
RETURN VALUE:
Sets `<font color="#82140F"><code>\.return_value</code></font>' to system status
`<font color="#82140F"><code>N status</code></font>'
</ul>
<p>
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