lessons/bash/ex4.html

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</style><title>ex4</title></head><body><article class="markdown-body"><h1 id="exercises-part-4"><a name="user-content-exercises-part-4" href="#exercises-part-4" class="headeranchor-link" aria-hidden="true"><span class="headeranchor"></span></a>Exercises. Part 4</h1>
<ul>
<li>Suppose that <code>ls</code> initially displays:</li>
</ul>
<pre><code>fructose.dat    glucose.dat   sucrose.dat
</code></pre>

<p>What is the output of:</p>
<pre><code>for datafile in *.dat
do    
    ls *.dat
done
</code></pre>

<ul>
<li>In the same directory, what is the effect of this loop?</li>
</ul>
<pre><code>for sugar in *.dat
do
    echo $sugar
    cat $sugar &gt; xylose.dat
done
</code></pre>

<ol>
<li>Prints fructose.dat, glucose.dat, and sucrose.dat, and copies sucrose.dat to create xylose.dat.</li>
<li>Prints fructose.dat, glucose.dat, and sucrose.dat, and concatenates all three files to create xylose.dat.</li>
<li>Prints fructose.dat, glucose.dat, sucrose.dat, and xylose.dat, and copies sucrose.dat to create xylose.dat.</li>
<li>None of the above.</li>
</ol>
<ul>
<li><code>expr</code> does very simple arithmetic using command-line parameters:</li>
</ul>
<pre><code>$ expr 3 + 5
8
$ expr 30 / 5 - 2
4
</code></pre>

<p>Given this, what is the output of:</p>
<pre><code>for left in 2 3
do
    for right in $left
    do
        expr $left + $right
    done
done
</code></pre>

<ul>
<li>What is the problem with multiplication with <code>expr</code>?  Can you <em>escape</em> the <code>*</code> so that it works as expected?</li>
</ul></article></body></html>