mand&nbsp;=&nbsp;string&nbsp;list<br>
&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;command_exists&nbsp;:&nbsp;?env:string&nbsp;array&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;string&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;bool<br>
&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;command&nbsp;:<br>
&nbsp;&nbsp;&nbsp;&nbsp;?verbose:bool&nbsp;<span class="keywordsign">-&gt;</span><br>
&nbsp;&nbsp;&nbsp;&nbsp;?env:string&nbsp;array&nbsp;<span class="keywordsign">-&gt;</span><br>
&nbsp;&nbs