# Defining a Filter

To create a filter for a watcher, press "New Filter" on the "Create New Watcher" window. Multiple filters can be created for the same watcher, and can be configured to perform different actions.

## Matching Options

For all types of filters, you may choose whether the filter action should be performed when the text does match the line or when it does not. This can be configured through the drop down box next to the search field.

Each filter can be created to be case sensitive or case insensitive. The default is case insensitive, which means that differences in capitalization are ignored.

## Simple Text Matching

The simplest way to construct a filter is to type in the text that you want to match. The filter will then search for that text in any part of the line.

## Regular Expressions

Filters support regular expressions that follow the Perl5 syntax. If you wish to make more complicated expression matching, you may want to look at the online Perl 5 Regular Expression documentation.

## Examples of Regular Expressions

To match a simple string, just type it in the search field:
`Error`
would match all lines that contains that text at any point within it.

To match a simple string that appears at the beginning of a line:
`^Error`

To match a simple string that appears at the end of a line:
`Error$`

To match a repeatition of digits that appears at exactly 4 in a row, such as a year:
`(\d){4}`

## Filter Actions

Each filter has an associated action with it. This action is performed for every line in the file that satisfies the matching options.

### Highlight Line

When the filter is matched, the line will be highlighted in the color chosen through the wizard. This can be helpful to flag unusual log messages such as warnings or error messages.

### Skip Line

When the filter is matched, the line will not be displayed in the LogWatcher window. This can be helpful for ignoring unimportant text.

### Add Todo Task

When the filter is matched, a Todo item is added to the Tasks list. The name and priority are configured through the new filter wizard.