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Chapter 15. Email

A thorough explanation of regular expressions is beyond the scope of this chapter. The structure of

Procmail recipes is more important, and useful sample Procmail recipes can be found at various places

on the Internet, including http://www.iki.fi/era/procmail/links.html. The proper use and adaptation of

the regular expressions found in these recipe examples depends upon an understanding of Procmail

recipe structure. Introductory information specific to basic regular expression rules can be found on

the

grep

man page.

A Procmail recipe takes the following form:

:0 flags :

lockfile name

*

special condition character

condition 1

 g 

*

special condition character

condition 2

 g 

*

special condition character

condition N

 g 

special action character

action to perform

The first two characters in a Procmail recipe are a colon and a zero. Various flags can optionally

be placed after the zero to control what Procmail does when processing this recipe. A colon after

the

flags

section specifies that a lockfile will be created for this message. If a lockfile is to be

created, you specify its name in the

lockfile name

space.

A recipe can contain several conditions to match against the message. If it has no conditions, every

message will match the recipe. Regular expressions are placed in some conditions in order to facilitate

a match with a message. If multiple conditions are used, they must all match in order for an action to

be performed. Conditions are checked based on the flags set in the recipe's first line. Optional special

characters placed after the

*

character can further control the condition.

The

action to perform

specifies what is to happen to a message if it matches one of the

conditions. There can only be one action per recipe. In many cases, the name of a mailbox is used

here to direct matching messages into that file, effectively sorting the email. Special action characters

may also be used before the action is specified.

15.5.2.1. Delivering vs. Non Delivering Recipes

The action used if the recipe matches a particular message determines whether recipe is considered

delivering or non delivering. A delivering recipe contains an action that writes the message to a file,

sends the message to another program, or forwards the message to another email address. A non 

delivering recipe covers any other actions, such as when a nesting block is used. A nesting block is an

action contained in braces

{ }

that designates additional actions to perform on messages that match

the recipe's conditions. Nesting blocks can be nested, providing greater control for identifying and

performing actions on messages.

Delivering recipes that match messages causes Procmail to perform the action specified and stop

comparing the message against any other recipes. Messages that match conditions in non delivering

recipes will continue to be compared against other recipes in the current and following

rc

files. In

other words, non delivering recipes cause the message to continue through the recipes after the spec 

ified action is taken on it.

15.5.2.2. Flags

Flags are very important in determining how or if a recipe's conditions are compared to a message.

The following flags are commonly used:

  A

  Specifies that this recipe will only be used if the last previous recipe without an

A

or

a

flag

also matched this message.