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<h2>2. Invoking PIC
<a name="2. Invoking PIC"></a>
</h2>
<p style="margin-top: 1em">Every <b>pic</b> description is
a little program describing drawing actions. The
<b>[gtn]roff</b>-dependent versions compile the program by
<i>pic</i>(1) into <i>gtroff</i>(1) macros; the
<i>pic2plot</i>(1) implementation uses a plotting library to
draw the picture directly. Programs that process or display
<i>gtroff</i>(1) output need not know or care that parts of
the image began life as <b>pic</b> descriptions.</p>
<p style="margin-top: 1em">The <i>pic</i>(1) program tries
to translate anything between <b>.PS</b> and <b>.PE</b>
markers, and passes through everything else. The normal
definitions of <b>.PS</b> and <b>.PE</b> in the <i>ms</i>
macro package and elsewhere have also the side-effect of
centering the <b>pic</b> output on the page.</p>
<h3>2.1. PIC Error Messages
<a name="2.1. PIC Error Messages"></a>
</h3>
<p style="margin-top: 1em">If you make a <b>pic</b> syntax
error, <i>gpic</i>(1) issues an error message in the
standard <i>gcc</i>(1)-like syntax. A typical error message
looks like this,</p>
<pre style="margin-left:10%; margin-top: 1em">pic:pic.ms:<nnn>: parse error before ‘<token>’
pic:pic.ms:<nnn>: giving up on this picture</pre>
<p style="margin-top: 1em">where ⟨nnn⟩ is a line
number, and ⟨token⟩ is a token near (usually just
after) the error location.</p>
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