@c This is part of the GNU Mailutils manual.
@c Copyright (C) 1999--2022 Free Software Foundation, Inc.
@c See file mailutils.texi for copying conditions.
@comment *******************************************************************
@pindex sieve
@UNREVISED

Sieve is a language for filtering e-mail messages at time of final
delivery, described in RFC 3028.  GNU Mailutils contains
stand-alone @dfn{sieve interpreter}, which is described in detail below.

@menu
* sieve interpreter::   A Sieve Interpreter
@end menu

@node sieve interpreter
@subsection A Sieve Interpreter

The sieve interpreter @command{sieve} allows you to apply Sieve scripts to
arbitrary number of mailboxes.  GNU @command{sieve} implements a superset
of the Sieve language as described in RFC 3028.  @xref{Sieve Language},
for a description of the Sieve language.  @xref{GNU Extensions}, for a
discussion of differences between the GNU implementation of Sieve and
its standard.

@menu
* Invoking Sieve::
* Sieve Configuration::
* Logging and Debugging::
* Extending Sieve::
@end menu

@node Invoking Sieve
@subsubsection Invoking @command{sieve}

The @command{sieve} invocation syntax is:

@example
sieve [@var{options}] @var{script}
@end example

Normally, @var{script} is the name of the disk file with the Sieve
script. If @var{script} is a single dash, the script is read from the
standard input. If the @option{-E} (@option{--expression}) option is
given, @var{script} is taken to be the sieve script text. 

@noindent
where @var{script} denotes the filename of the sieve program to parse,
and @var{options} is one or more of the following:

@table @option
@item -c
@itemx --compile-only
Compile script and exit.

@item --clear-library-path
@itemx --clearpath
Clear Sieve library path.  See also @ref{Sieve Configuration,
clear-library-path}.

@item --clear-include-path
Clear Sieve include path.  See also @ref{Sieve Configuration,
clear-include-path}. 

@item -d[@var{flags}]
@itemx --debug[=@var{flags}]
Specify debug flags.  The @var{flags} argument is a sequence of one or
more of the following letters:

@multitable @columnfractions .40 .45
@item @samp{g} @tab Enable main parser traces
@item @samp{T} @tab Enable mailutils traces
@item @samp{P} @tab Trace network protocols
@item @samp{t} @tab Enable sieve trace
@item @samp{i} @tab Trace the program instructions
@end multitable

@item -D
@itemx --dump
Compile the script, dump disassembled code on standard output and exit.

@item --environment=@var{name}=@var{value}
Set sieve environment variable @var{name} to the @var{value}.

@item -e @var{address}
@itemx --email @var{address}
Override the user email address.  This is useful for @code{reject} and
@code{redirect} actions.  By default, the user email address is deduced
from the user name and the full name of the machine where
@command{sieve} is executed.  See also @ref{Sieve Configuration,
email}. 

@item -E,
@itemx --expression
Treat the @var{script} argument as Sieve program text.

@item -I @var{dir}
@itemx --includedir=@var{dir}
Append directory @var{dir} to the list of directories searched for
include files.  See also @ref{Sieve Configuration, include-path}.

@item -f
@itemx --mbox-url=@var{mbox}
Mailbox to sieve (defaults to user's system mailbox).  See also
@ref{Sieve Configuration, mbox-url}.

@item -k
@itemx --keep-going
Keep on going if execution fails on a message.  See also
@ref{Sieve Configuration, keep-going}.

@item -L @var{dir}
@itemx --libdir=@var{dir}
Append directory @var{dir} to the list of directories searched for
library files.  See also @ref{Sieve Configuration, library-path}.

@item --libdir-prefix=@var{dir}
Add @var{dir} to the beginning of the list of directories searched for
library files.

@item --line-info=@var{bool}
Print source location along with action logs (default).

@item -M @var{url}
@itemx --mailer=@var{url}
Define the URL of the default mailer.

@item -n
@itemx --no-actions
@itemx --dry-run
Dry run: do not execute any actions, just print what would be done.

@item --no-program-name
Do not prefix diagnostic messages with the program name.

@item -t @var{ticket}
@itemx --ticket=@var{ticket}
Ticket file for mailbox authentication.  See also
@ref{Sieve Configuration, ticket}.

@item --variable=@var{name}=@var{value}
Set Sieve variable @var{name}. This option automatically inserts
@samp{require "variables"} at the top of the script.

@item -v
@itemx --verbose
Log all actions executed.  See also @ref{Sieve Configuration, verbose}.
@end table

See also @ref{Common Options}.

@node Sieve Configuration
@subsubsection Sieve Configuration

The behavior of @command{sieve} is affected by the following
configuration statements:

@multitable @columnfractions 0.3 0.6
@headitem Statement @tab Reference
@item debug         @tab @xref{debug statement}.
@item tls           @tab @xref{tls statement}.
@item mailbox       @tab @xref{mailbox statement}.
@item locking       @tab @xref{locking statement}.
@item logging       @tab @xref{logging statement}.
@item mailer        @tab @xref{mailer statement}.
@end multitable

The following statements configure sieve-specific features:

@deffn {Sieve Conf} sieve @{ ...  @}
This block statement configures search paths @command{sieve} uses to
locate its loadable modules.  @xref{Require Statement}, for a detailed
information about loadable modules.

This statement may contain the following sub-statements:

@deffn {Sieve Conf} clear-library-path @var{bool}
If @var{bool} is @samp{true}, clear library search path.
@end deffn

@deffn {Sieve Conf} clear-include-path @var{bool}
If @var{bool} is @samp{true}, clear include search path.
@end deffn

@deffn {Sieve Conf} library-path @var{path}
Add directories to @command{sieve} library search path.  Argument is a
string containing a colon-separated list of directories.
@end deffn

@deffn {Sieve Conf} library-path-prefix @var{path}
Add directories to the beginning if the library search path.  Argument
is a string containing a colon-separated list of directories.
@end deffn

@deffn {Sieve Conf} include-path @var{path}
Add directories to the include search path.  Argument is a
string containing a colon-separated list of directories.
@end deffn
@end deffn

@deffn {Sieve Conf} keep-going @var{bool}
If @var{bool} is @samp{true}, do not abort if execution of a Sieve
script fails on a particular message.
@end deffn

@deffn {Sieve Conf} mbox-url @var{url}
Sets @acronym{URL} of the mailbox to be processed.
@end deffn

@deffn {Sieve Conf} ticket @var{file}
Sets the name of the ticket file for user authentication.
@end deffn

@deffn {Sieve Conf} debug @var{flags}
Sets Sieve debug flags.  @xref{Logging and Debugging}, for a detailed
description.
@end deffn

@deffn {Sieve Conf} verbose @var{bool}
If @var{bool} is @samp{true}, log all executed actions.
@end deffn

@deffn {Sieve Conf} line-info @var{bool}
If @var{bool} is @samp{true}, print source locations along with action
logs.  This statement takes effect only if @code{verbose true} is also
set.
@end deffn

@deffn {Sieve Conf} email @var{addr}
Set user e-mail address.  This is useful for @code{reject} and
@code{redirect} actions.  By default, the user email address is deduced
from the user name and the full name of the machine where @command{sieve} is
executed. 
@end deffn

@node Logging and Debugging
@subsubsection Logging and debugging

The default behavior of @command{sieve} is to remain silent about
anything except errors.  However, it is sometimes necessary to see
which actions are executed and on which messages.  This is particularly
useful when debugging the sieve scripts.  The @option{--verbose}
(@option{-v}) option outputs log of every action executed.

Option @option{--debug} allows to produce even more detailed debugging
information.  This option takes an argument specifying the
debugging level to be enabled.  The argument can consist of the
following letters:

@table @samp
@item t
This flag enables sieve tracing.  It means that every test will be logged
when executed.

@item T
This flag enables debugging of underlying @code{mailutils} library.

@item P
Trace network protocols: produces log of network transactions executed
while running the script.

@item g
Enable main parser traces.  This is useful for debugging the sieve grammar.

@item i
Trace the program instructions.  It is the most extensive debugging
level.  It produces the full execution log of a sieve program, showing
each instruction and states of the sieve machine.  It is only useful
for debugging the code generator.
@end table

@emph{Note}, that there should be no whitespace
between the short variant of the option (@option{-d}), and its
argument.  Similarly, when using long option (@option{--debug}),
its argument must be preceded by equal sign.

If the argument to @option{--debug} is omitted, it defaults to
@samp{TPt}. 

Option @option{--dump} produces the disassembled dump of the compiled
sieve program. 

By default @command{sieve} outputs all diagnostics on standard error and verbose
logs on standard output.  This behaviour is changed when
@option{--log-facility} is given in the command line (@FIXME-pxref{logging}).
This option causes @command{sieve} to output its diagnostics to
the given syslog facility.

@node Extending Sieve
@subsubsection Extending @command{sieve}

The basic set of sieve actions, tests and comparators may be extended
using loadable extensions.  The usual @code{require} mechanism is used for
that.

When processing arguments for @code{require} statement, @command{sieve}
uses the following algorithm:

@enumerate 1
@item Look up the name in a symbol table.  If the name begins with
@samp{comparator-} it is looked up in the comparator table.  If it
begins with @samp{test-}, the test table is searched instead.  Otherwise
the name is looked up in the action table.

@item If the name is found, the search is terminated.

@item Otherwise, transform the name.  First, any @samp{comparator-} or
@samp{test-} prefix is stripped.  Then, any character other than
alphanumeric characters, @samp{.} and @samp{,} is replaced with
dash (@samp{-}).  The name thus obtained is used as a file name
of an external loadable module. 

@item Try to load the module.  The module is searched in the
following search paths (in the order given):

@enumerate 1
@item Mailutils module directory.  By default it is
@file{$prefix/lib/mailutils}.

@item The value of the environment variable @env{LTDL_LIBRARY_PATH}.

@item Additional search directories specified with the.
@option{--libdir-prefix} command line option (@pxref{Invoking Sieve,
libdir-prefix}), or the @code{library-path-prefix} configuration
statement (@pxref{Sieve Configuration,library-path-prefix}).

@item Additional search directories specified with the
@code{library-path} statement (@pxref{Sieve Configuration,
library-path}) in Sieve configuration file.

@item Additional search directories specified with the.
@option{--libdir} command line option (@pxref{Invoking Sieve,libdir}).

@item Additional search directories specified with the
@code{#searchpath} Sieve directive (@pxref{#searchpath}).

@item System library search path: The system dependent library
search path (e.g. on Linux it is set by the contents of the file
@file{/etc/ld.so.conf} and the value of the environment variable
@env{LD_LIBRARY_PATH}).
@end enumerate

The value of @env{LTDL_LIBRARY_PATH} and @env{LD_LIBRARY_PATH} must be
a colon-separated list of absolute directories, for example,
@samp{"/usr/lib/mypkg:/lib/foo"}.

In any of these directories, @command{sieve} first attempts to find
and load the given filename.  If this fails, it tries to append the
following suffixes to the file name:

@enumerate 1
@item the libtool archive extension @samp{.la}

@item the extension used for native dynamic libraries on the host
platform, e.g., @samp{.so}, @samp{.sl}, etc.
@end enumerate

@item If the module is found, @command{sieve} executes its
initialization function (see below) and again looks up the name
in the symbol table.  If found, search terminates successfully.

@item If either the module is not found, or the symbol wasn't
found after execution of the module initialization function,
search is terminated with an error status.  @command{sieve} then displays
the following diagnostic message:

@example
source for the required action NAME is not available
@end example
@end enumerate