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<div class="header">
  <img src="../../png/ioccc.png" alt="IOCCC image by Matt Zucker" width=300 height=110>
  <h1>The International Obfuscated C Code Contest</h1>
  <h2>1990/tbr - Best Utility</h2>
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<div class="topnav">
  <a class="Left" href="../stig/index.html">&larr; stig</a>
  <a class="Left" href="../index.html">&uarr; 1990 &uarr;</a>
  <a class="Left" href="../theorem/index.html">theorem &rarr;</a>
  <a class="Right" href="https://github.com/ioccc-src/temp-test-ioccc/1990/tbr/tbr.c">C code</a>
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<h2 id="authors"><a name="author"></a>Authors:</h2>
<ul>
<li>Name: <a href="../../authors.html#Byron_Rakitzis">Byron Rakitzis</a><br>
Location: <a href="../../location.html#US">US</a> - <em>United States of America</em> (<em>United States</em>)
<br><br></li>
<li>Name: <a href="../../authors.html#Sean_Dorward">Sean Dorward</a><br>
Location: <a href="../../location.html#ZZ">ZZ</a> - <em>Unknown location</em></li>
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<h2 id="to-build">To build:</h2>
<pre class="&lt;!---sh--&gt;"><code>    make all</code></pre>
<p>The authors provided another version of this program. See the <a href="#alternate-code">alternate
version</a> section below.</p>
<h3 id="bugs-and-misfeatures">Bugs and (Mis)features:</h3>
<p>The current status of this entry is:</p>
<pre><code>    STATUS: INABIAF - please **DO NOT** fix</code></pre>
<p>For more detailed information see <a href="../../bugs.html#1990_tbr">1990 tbr bugs</a>.</p>
<h3 id="a-note-about-the-fixes-of-this-entry-in-2023">A note about the fixes of this entry in 2023:</h3>
<p>In 2023 it was noticed that in some systems like macOS there was confusing
output due to a warning at runtime that was interspersed with the output of the
program. For instance it would show:</p>
<pre class="&lt;!---sh--&gt;"><code>    ./tbr
    $ warning: this program uses gets(), which is unsafe.</code></pre>
<p>which kind of hid the prompt. Thus the entry was changed to use <code>fgets(3)</code> which
is referred to later in this file.</p>
<p>Also <code>exit(3)</code> returns <code>void</code> but the entry was using it in a binary expression so
this entry would not compile in modern systems. This fix is also referred to
below, in the <a href="#alternate-code">alternate version</a> section.</p>
<h2 id="to-use">To use:</h2>
<pre class="&lt;!---sh--&gt;"><code>    ./tbr
    $ enter some shell commands</code></pre>
<p>NOTE: globs do not work with this entry. Why?</p>
<p>NOTE: <code>exit</code> does not work and neither does <code>logout</code>. To exit try sending ctrl-d
or ctrl-c (or kill it from another terminal :-) ). But why does it not work with
just <code>exit</code> or <code>logout</code>? Hint: see the authors’ remarks.</p>
<h2 id="try">Try:</h2>
<pre class="&lt;!---sh--&gt;"><code>    ./tbr
    $ ls -l tbr tbr.c

    # notice how the following does not work:
    ls tbr*

    # try figuring out how this entry works in an editor:
    vi tbr.c

    # then figure out how to exit vi :-)</code></pre>
<p>What happens if you try using <code>cd -</code> to return to previous directory? What about
<code>cd</code> with no args?</p>
<p>The authors include a section called <a href="#bugs">BUGS</a> that, because they were
documented, are not considered bugs as such in the context of the contest.</p>
<h2 id="alternate-code">Alternate code:</h2>
<p>The authors supplied us with a slightly smaller unformatted version
of the program which we include below:</p>
<pre class="&lt;!---c--&gt;"><code>    #define D ,close(
    char*c,q[512],m[256],*v[99],**u,*i[3];int f[2],p;main(){for(m[m[60]=m[62]=
    32]=m[*m=124[m]=9]=6;e(-8),gets(1+(c=q))||(exit(0),0);r(0,0))for(;*++c;);}
    r(t,o){*i=i[2]=0;for(u=v+98;m[*--c]^9;m[*c]&amp;32?i[*c&amp;2]=
    *u,u-v^98&amp;&amp;++u:3)if(!m[*c]){for(*++c=0;!m[*--c];);*--u=
    ++c;}u-v^98?strcmp(*u,&quot;cd&quot;)?*c?pipe(f),o=f[1]:1,(p=fork())?e(p),o?
    r(o,0)D o)D*f):4,wait(0):(o?dup2(*f,0)D*f)D o):*i?1 D
    0),e(open(*i,0)):5,t?dup2(t,1)D t):i[2]?9 D
    1),e(creat(i[2],438)):2,e(execvp(*u,u))):e(chdir(u[1])*2):6;}
    e(x){x&lt;0?write(2,&quot;?\n$ &quot;-x/4,2),x+1||(exit(1),0):5;}</code></pre>
<p>and in the <a href="tbr.alt.c">alternate source</a>. It has the <code>exit()</code> returns <code>void</code> fix
as well as the <code>gets()</code> to <code>fgets()</code> fix applied to it to make it functionally
equivalent like the authors intended.</p>
<h3 id="alternate-build">Alternate build:</h3>
<pre class="&lt;!---sh--&gt;"><code>    make alt</code></pre>
<h3 id="alternate-use">Alternate use:</h3>
<pre class="&lt;!---sh--&gt;"><code>    ./tbr.alt</code></pre>
<h2 id="judges-remarks">Judges’ remarks:</h2>
<p>This program touches on a well known Unix utility, the 6th edition Bourne Shell
(<code>/bin/sh</code>), whose original source was considered to be extremely obfuscated by
many people (although Steve Bourne might disagree). Did you know that the Bourne
Shell source was a major inspiration for the formation of the IOCCC back in
1984?</p>
<h2 id="authors-remarks">Authors’ remarks:</h2>
<p>This program is a rudimentary shell. It does I/O redirection, pipes
and cd. It flags errors on failed <code>chdir()</code>, <code>open()</code>, <code>creat()</code>,
<code>execvp()</code>, <code>fork()</code> and a few syntax errors.</p>
<p>This program is obfuscated in a few notable ways: apart from the layout (an
unformatted (but crunched) version is included for people who want to put this
through <code>cb</code>) it makes clever use of a <code>write()</code> statement, so that the same statement
can be used to print errors and the prompt. By calling the error function with
the value <code>-8</code>, the pointer offset in the expression <code>"?\n$ "-x/4</code> goes from 0
to 2. Presto! A prompt. For errors with numbers smaller than <code>-4</code> (i.e., UNIX
system calls) a question mark is printed.</p>
<p>The error value of <code>chdir()</code> is doubled so that we don’t exit from the parent
shell on a <code>chdir()</code> error (since <code>e()</code> exits on <code>-1</code> errors only). All other
system call failures exit since they are from sub-shells.</p>
<p>Recursion is sneakily employed to avoid a second call to <code>fork()</code>,
and the line is parsed in a fairly bizarre fashion: backwards. The
heart of the program, that is, the part which performs all <code>fork()</code>s,
<code>exec()</code>s, <code>open()</code>s, etc. is ONE C STATEMENT.</p>
<p>The meta-values array is initialized in a bizarre fashion, and the
subsequent checks for the <code>'&lt;'</code> and <code>'&gt;'</code> are performed in a single
statement using a mask, since you know that <code>'&gt;'&amp;2</code> is 0, whereas
<code>'&lt;'&amp;2</code> is 2. Other such micro-obfuscations abound.</p>
<p>Finally, it is notable that the code was hacked for minimality. If
you look at the compressed version, you will be hard-pressed to
eliminate more than a few characters (we can’t see how to make it
any smaller!). 550 characters is pretty lean for a shell that does
this much.</p>
<h3 id="bugs">BUGS</h3>
<p>The syntax of the shell has not been fully explored, but if you try
to redirect in the same direction more than once, only one
redirection is performed. This is a “feature” of the way the line
is parsed; a pointer to the stack of arguments is assigned and an
argument is stolen every time a <code>&gt;</code> or <code>&lt;</code> is encountered. The
shell flags an error if no arguments are on the stack. Thus, for
example:</p>
<pre class="&lt;!---sh--&gt;"><code>    cat &gt; foo &gt; bar</code></pre>
<p>cats to <code>foo</code>, since it was pushed last, but</p>
<pre class="&lt;!---sh--&gt;"><code>    cat &gt; &gt; foo bar</code></pre>
<p>cats to <code>bar</code>, since <code>bar</code> was pushed under <code>foo</code> (remember we’re
parsing right-left).</p>
<p>Depending on your flavor of Unix, <code>cd</code> without an argument will
either produce an error or just do nothing.</p>
<p>There is just one error message, the question mark, but hey, that’s
all <code>ed(1)</code> does too.</p>
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<h1 id="inventory-for-1990tbr"><a name="inventory"></a>Inventory for 1990/tbr</h1>
<p><a href="#top">Jump to top</a></p>
<h2 id="primary-files">Primary files</h2>
<ul>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1990/tbr/tbr.c">tbr.c</a> - entry source</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1990/tbr/Makefile">Makefile</a> - entry Makefile</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1990/tbr/tbr.alt.c">tbr.alt.c</a> - alternative source</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1990/tbr/tbr.orig.c">tbr.orig.c</a> - original source</li>
<li><a href="1990_tbr.tar.bz2">1990_tbr.tar.bz2</a> - download entry</li>
</ul>
<h2 id="secondary-files">Secondary files</h2>
<ul>
<li><a href="index.html">index.html</a> - this web page</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1990/tbr/README.md">README.md</a> - markdown source for index.html</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1990/tbr/.entry.json">.entry.json</a> - description of entry in JSON</li>
<li><a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1990/tbr/.gitignore">.gitignore</a> - list of files that should not be committed under git</li>
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