View source for Command-line interface on Linux/UNIX

This is not a UNIX guide, but just a loose list of tips, hints, etc., that may come in handy when working in a command-line environment.

=== Bash ===

<ul>

<li><span id="inverted-quotes"></span>To use the output of one command as the input for the next command, use back quotes ("inverted commas") around the first command. This is called [http://en.wikipedia.org/wiki/Command_substitution command substitution].
</li>

</ul>

=== Useful (and sometimes underappreciated) command-line tools ===

<ul>

<li>To combine files side-by-side into a single file use
<pre>
paste file1 file2 ... > output
</pre>
If <tt>file1</tt>, <tt>file2</tt>, ... contain the same number of lines, <tt>output</tt> will contain their contents as columns.
</li>

<li><span id="which"></span>You may have many entries in your <tt>PATH</tt> variable, or there may be multiple copies of an executable on a file system. To determine which version of ''program'' will be executed, use
<pre>
which program
</pre>
</li>

<li>To find out which libraries are needed/used by a dynamically linked executable, use
<pre>
ldd /path/program
</pre> 
Note that <tt>ldd</tt> will not use <tt>PATH</tt> to search for ''program''; just must specify it via an explicit path. However, you can take advantage of <tt>[[#which|which]]</tt> as follows
<pre>
ldd `which program`
</pre>
Note the <tt>[[#inverted-quotes|back quotes]]</tt>. Side note: On OS X, if you have <tt>xcode</tt> installed the <tt>ldd</tt> command can be mimicked via <tt>otool -L</tt>.
</li>

</ul>