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216 Chapter 16. Email

If you would like to ignore "Program failure" messages when deciding whether a ﬁlter or action

succeeded, use the W option instead.

Additional ﬂags can be found in the procmailrc man page.

16.5.2.3. Specifying a Local Lockﬁle

Lockﬁles are very useful with Procmail to ensure that more than one process does not try to alter a

certain message at the same time. You can specify a local lockﬁle by placing a colon (:) after any

ﬂags on a recipe’s ﬁrst line. This will create a local lockﬁle based on the destination ﬁlename plus

whatever has been set in the LOCKEXT global environment variable.

Alternatively, you can specify the name of the local lockﬁle to be used with this recipe after the colon.

16.5.2.4. Special Conditions and Actions

Particular characters used before Procmail recipe conditions and actions change the way they are

interpreted.

The following characters may be used after the * character at the beginning of a recipe’s condition

line:

• ! — Inverts the condition, causing a match to occur only if the condition does not match the

message.

•

— Checks to see if the message is under the speciﬁed number of bytes.

• — Checks to see if the message is over a particular number of bytes.

The following characters are used to perform special actions:

• ! — Tells Procmail to forward the message to the speciﬁed email addresses

• $ — Refers to a variable set earlier in the rc ﬁle. This is usually used to set a common mailbox that

will be referred to by various recipes.

• | — The pipe character tells Procmail to start a speciﬁc program to deal with this message.

• { and } — Constructs a nesting block, used to contain additional recipes to apply to matching

messages.

If no special character is used at the beginning of the action line, then Procmail assumes that the action

line is specifying a mailbox where the message should be written.

16.5.2.5. Recipe Examples

Procmail is an extremely ﬂexible program, allowing you to match messages with very speciﬁc condi-

tions and then perform detailed actions on them. As a result of this ﬂexibility, however, composing a

Procmail recipe from scratch to achieve a certain goal can be difﬁcult for new users.

The best way to develop the skills to build Procmail recipe conditions stems from a strong understand-

ing of regular expressions combined with looking at many examples built by others. The following

very basic examples exist to serve as a demonstration of the structure of Procmail recipes and can

provide the foundation for more intricate constructions.

The most basic recipes does not even contain conditions, as is demonstrated in Figure 16-10.

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 216