====== Grep - Regex Usage ======

A regular expression is a compact way of describing complex patterns in text.

With grep, you can use them to search for patterns

----

Assuming a file exists with the following contents:

<file>
boot
book
booze
machine
boots
bungie
bark
aardvark
broken$tuff
robots
</file>

----

===== Basic Regex Search =====

Search the file for lines ending with the letter e.

<code bash>
grep "e$" filename
</code>

returns:

<code bash>
booze
machine
bungie
</code>

----

===== Extended Regex Search =====

<code bash>
grep -E "boots?" filename
</code>

returns:

<code bash>
boot
boots
</code>

<WRAP info>
**NOTE:**  **grep -E** is also known as egrep.

The regexp command ? will match 1 or 0 occurrences of the previous character.

</WRAP>

----

===== Combine Multiple Searches =====

<code bash>
grep -E "boot|boots" filename
</code>

returns:

<code bash>
boot
boots
</code>

<WRAP info>
**NOTE:**  The pipe **|** means 'or'.

</WRAP>

----

===== Special Characters =====

<code bash>
grep '\$' filename
</code>

returns:

<code bash>
broken$tuff
</code>

<WRAP info>
**NOTE:**  

The **-F-- option can also be used, which stands for 'fixed string' or 'fast' in that it only searches for literal strings and not regexps.

</WRAP>