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><span id="paste"></span>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>Splitting files.
To split a file into parts that each contain <tt>N</tt> lines (except possibly for the last chunk) and that will be labeled "out00", "out01", etc., use
<pre>
split -d -l N file out
</pre>
For more than 100 chunks, use the <tt>-a</tt> option (see <tt>man split</tt>).

To instead split a file into a fixed number (M) of chunks, use
<pre>
split -d -n M file out
</pre>
</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><span id="textdiff"></span>Comparing text files.  To find out if two files are identical except for differences in white space, use
<pre>
diff -w file1 file2
</pre>
To compare two text files in which lines may have been rewrapped, use [http://www.gnu.org/software/wdiff wdiff] ('word diff')
<pre>
wdiff -3 file1.tex file2.tex
</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>