If the user types carriage-return, or if the
command-line flag `<font color="#82140F"><code>-y</code></font>' was specified when invoking Gri, the value
100 will be assigned to `<font color="#82140F"><code>.num.</code></font>').
For example, 
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<PRE>
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query .num. "Number of rows to read?" (100)
read columns .num. x y
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Gri allows you to use a previous value of the variab