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<h1 style="margin-bottom:0;padding-bottom:0;">Compiling BrainFuck with a shell script</h1>
<em>That was easy</em>
<br><br>
<p><a rel="noopener" target="_blank" href="https://en.wikipedia.org/wiki/Brainfuck">BrainFuck</a> is an <a rel="noopener" target="_blank" href="https://en.wikipedia.org/wiki/Esoteric_programming_language">esoteric programming language</a> that is surprisingly easy to implement. It is almost on the same level as &quot;Hello, world!&quot;, but for compilers and interpreters. In this post, ill share my new little BrainFuck compiler I built with a bash script.</p>
<h2 id="the-brainfuck-instruction-set">The BrainFuck instruction set</h2>
<p>BrainFuck has 8 simple instructions:</p>
<table><thead><tr><th>Instruction</th><th>Operation</th></tr></thead><tbody>
<tr><td><code>&gt;</code></td><td>increment data pointer</td></tr>
<tr><td><code>&lt;</code></td><td>decrement data pointer</td></tr>
<tr><td><code>+</code></td><td>increment the byte at the data pointer</td></tr>
<tr><td><code>-</code></td><td>decrement the byte at the data pointer</td></tr>
<tr><td><code>.</code></td><td>print the current byte to stdout</td></tr>
<tr><td><code>,</code></td><td>read one byte from stdin to the current byte</td></tr>
<tr><td><code>[</code></td><td>jump to the matching <code>]</code> if the current byte is 0</td></tr>
<tr><td><code>]</code></td><td>jump to the matching <code>[</code> if the current byte is nonzero</td></tr>
</tbody></table>
<h3 id="the-c-equivalent">The C equivalent</h3>
<p>BrainFuck works on a &quot;tape&quot;. This is essentially a massive array, with a pointer that moves around. Luckily, this can be implemented with a tiny bit of C. (Thanks <a rel="noopener" target="_blank" href="https://en.wikipedia.org/wiki/Brainfuck#Commands">wikipedia</a>)</p>
<table><thead><tr><th>BF</th><th>C code</th></tr></thead><tbody>
<tr><td><code>&gt;</code></td><td><code>++ptr;</code></td></tr>
<tr><td><code>&lt;</code></td><td><code>--ptr;</code></td></tr>
<tr><td><code>+</code></td><td><code>++*ptr;</code></td></tr>
<tr><td><code>-</code></td><td><code>--*ptr;</code></td></tr>
<tr><td><code>.</code></td><td><code>putchar(*ptr);</code></td></tr>
<tr><td><code>,</code></td><td><code>*ptr=getchar();</code></td></tr>
<tr><td><code>[</code></td><td><code>while (*ptr) {</code></td></tr>
<tr><td><code>]</code></td><td><code>}</code></td></tr>
</tbody></table>
<h2 id="implementation">Implementation</h2>
<p>Due to the fact BF has a direct conversion to C, I figured: <em>&quot;Why not just use <a rel="noopener" target="_blank" href="https://www.gnu.org/software/sed/manual/sed.html">sed</a> to make a BF compiler?&quot;</em>. And so I did.</p>
<p>The script is available at <a rel="noopener" target="_blank" href="https://git.io/JvIHm">git.io/JvIHm</a>, and works as follows:</p>
<ol>
<li>Create a file containing a &quot;header&quot; that contains some C code that imports <code>stdio.h</code> and creates a char array</li>
<li>Use SED to replace all BF instructions with the matching C code</li>
<li>Append a file footer with code to return the current value at the program pointer</li>
<li>Compile this c file with <a rel="noopener" target="_blank" href="https://gcc.gnu.org/">GCC</a></li>
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