Foglight for Infrastructure 5.9.2 - User Guide

Regular expression basics

The simplest regular expression is a basic text string containing only alphanumeric characters. For example, Host1, matches the same value, Host1.

A regular expression is fundamentally different from a pattern using file name wild cards such as an asterisk ‘*’ or a question mark ‘?’. For example, issuing a search in Windows® Explorer using *.jpg as a filter matches all files with the .jpg extension.

This is not a regular expression, it is a simple filter that uses wild cards. An equivalent regular expression that selects all files with the .jpg extension is .*\\.jpg. The details of this regular expression are covered next.

For more details, see these topics:

Building a simple pattern

In this section we look at a simple regular expression pattern that selects all hosts whose names start with Host. The completed expression is Host.*. This expression contains two special characters:

The final expression, Host.*, results in matching any strings that start with Host and match any of the following host names:

However, the following host names do not match this expression:

We now take a look at a simple pattern that matches a group of similar text strings. A common pattern for selecting Windows® drive names is C:.*. A typical usage of this expression is in the Excluded Drives property of the WindowsAgent.

Unlike in a simple file matching filter, C:*, the equivalent regular expression requires a period between the colon ‘:’ and the asterisk ‘*’: C:.*.

CAUTION: Failing to include a period in this particular example can result in data loss.

Next, we build a regular expression that selects all hosts whose name include the string Host, not just the ones that start with Host. To do that, simply add a prefix to the above expression, Host.*, resulting in .*Host.*.

This expression matches any hosts that include Host, but not necessarily begin with it. That is because the prefix .* translates to any combination of zero or more characters appearing before the string Host. The expression matches each of the following host names:

Building a pattern that matches a specific character

A regular expression pattern can be used to match a string that includes a specific character. For example, you can build a pattern that matches only the drive letters C through H. To do this, you have two options:

Choosing the second option, the resulting regular expression is: [C-H]:.*. This means, any letter in the range and including ‘C’ through ‘H’, followed by a colon ‘:’, and optionally by more characters.

Building a pattern that matches multiple characters

Using regular expressions you can define a pattern to match a multi-character pattern. For example, you can write a regular expression to match all hosts whose names contain Host and are followed by exactly two digits. That means you want to match the following strings:

But not:

The expression that matches this pattern is: Host[0-9][0-9].

TIP: Because there is no trailing .* in the expression, the host name with the -bckp suffix does not match.

Going further, you can write an expression that matches all hosts whose names contain Host, followed by exactly two digits, and optionally a lowercase letter. That means you want to match the following strings:

But still not:

The expression that matches this pattern is: Host[0-9][0-9][a-z]?.

NOTE: The question mark ‘?’ in regular expressions is also a quantifier, and not a single character wild character like in some file systems.