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copied!<blockquote> <p>this works:</p> <pre><code>nc shldvgfas005 6155 < temp.6153 </code></pre> <p>this hangs:</p> <pre><code>cmd="nc shldvgfas005 6153 < temp.6153"; $cmd </code></pre> </blockquote> <p>The difference you see here is due to the shell parsing redirection operators before parameter expansions.</p> <blockquote> <p>this gives an error:</p> <pre><code>cmd="nc shldvgfas005 6153 < temp.6153"; "$cmd" -bash: nc shldvgfas005 6153 < temp.6153: command not found </code></pre> </blockquote> <p>This command fails because the quotes around the parameter expansion prevent it from being split into multiple fields. The shell tries to find a single executable named <code>nc shldvgfas005 6153 < temp.6153</code> (i.e. there are embedded spaces in the filename), but fails to find any such file. Also, the redirection does not happen due to the same reason as the first failure.</p> <p>For the details of your shell’s parsing, consult its manual (or that of a related shell; possibly the <a href="http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html" rel="nofollow noreferrer">POSIX Shell Command Language specification</a>). In general, all Bourne-like shells parse redirections before expansions. So the redirection operator can not be part of a variable (though the redirection source/target (filename) can be a variable). Some folks like to use <em>eval</em> to make stuff like this work, but it is a bad idea unless you are fully aware of the security implications.</p>

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