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<title>execline: the runblock program</title>
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<p>
<a href="index.html">execline</a><br />
<a href="//skarnet.org/software/">Software</a><br />
<a href="//skarnet.org/">www.skarnet.org</a>
</p>
<h1> The <tt>runblock</tt> program </h1>
<p>
<tt>runblock</tt>'s purpose is to help you write execline commands
in the execline language. It can only be used inside an execline
script. If the script has been given blocks as arguments, <tt>runblock</tt>
allows you to execute one of the blocks individually.
</p>
<h2> Interface </h2>
<pre>
runblock [ -P ] [ -n <em>argshift</em> ] [ -r ] <em>n</em>
</pre>
<ul>
<li> <tt>runblock</tt> skips the first <em>argshift</em> positional
parameters. It does that to allow you to design commands that take simple
arguments <em>and</em> blocks. </li>
<li> Then <tt>runblock</tt> looks for and parses
<a href="el_semicolon.html">blocks</a> in the positional parameters. </li>
<li> If the <tt>-r</tt> option is present: <tt>runblock</tt> skips
<em>n</em> blocks and execs into the remaining arguments. </li>
<li> Else it skips <em>n</em>-1 blocks and execs into the <em>n</em>th
one. </li>
<li> Normally <tt>runblock</tt> <a href="el_pushenv.html#pop">pops</a>
its environment frame before executing. If the <tt>-P</tt> option has
been given, it <em>does not</em> pop. </li>
<li> Of course, if the block structure doesn't match, <tt>runblock</tt>
exits 100 with an error message. </li>
</ul>
<h2> Example: implementing the <a href="ifelse.html">ifelse</a> command </h2>
<p>
Suppose that we want to implement the <a href="ifelse.html">ifelse</a> command as
an execline script, using the <a href="ifte.html">ifte</a> command.
<tt>runblock</tt> allows us to do it in a simple way:
</p>
<pre>
#!/command/execlineb
ifte { runblock 2 } { runblock -r 2 } runblock 1
</pre>
<p>
That's it.
</p>
<h2> Credits </h2>
<p>
The <tt>runblock</tt> idea, as well as the <tt>ifelse</tt> idea, comes
from <a href="http://code.dogmap.org/">Paul Jarc</a>.
</p>
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