\input texinfo
@c %**start of header
@setfilename ../../info/erc.info
@settitle ERC Manual
@set ERCVER 5.6.1
@set ERCDIST as distributed with Emacs @value{EMACSVER}
@include docstyle.texi
@syncodeindex fn cp
@include emacsver.texi
@c %**end of header

@copying
This manual is for ERC @value{ERCVER} @value{ERCDIST}.

Copyright @copyright{} 2005--2024 Free Software Foundation, Inc.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,''
and with the Back-Cover Texts as in (a) below.  A copy of the license
is included in the section entitled ``GNU Free Documentation License''.

(a) The FSF's Back-Cover Text is: ``You have the freedom to copy and
modify this GNU manual.''

All Emacs Lisp code contained in this document may be used, distributed,
and modified without restriction.
@end quotation
@end copying

@dircategory Emacs network features
@direntry
* ERC: (erc).                   Powerful and extensible IRC client for Emacs.
@end direntry

@titlepage
@title ERC manual
@subtitle a full-featured IRC client
@subtitle for Emacs

@c The following two commands
@c start the copyright page.
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@contents

@ifnottex
@node Top
@top ERC

@insertcopying
@end ifnottex

@menu
* Introduction::                What is ERC?
* Getting Started::             Quick Start guide to using ERC.
* Keystroke Summary::           Keystrokes used in ERC buffers.
* Modules::                     Available modules for ERC.
* Advanced Usage::              Cool ways of using ERC.
* Getting Help and Reporting Bugs::
* History::                     The history of ERC.
* GNU Free Documentation License::  The license for this documentation.
* Concept Index::               Search for terms.

@detailmenu
 --- The Detailed Node Listing ---

Getting Started

* Sample Session::              Example of connecting to the @samp{#emacs} channel
* Special Features::            Differences from standalone IRC clients

Advanced Usage

* Connecting::                  Ways of connecting to an IRC server.
* SASL::                        Authenticating via SASL.
* Sample Configuration::        An example configuration file.
* Integrations::                Integrations available for ERC.
* Module Loading::              How ERC loads modules.
* Match API::                   Custom matching and highlighting.
* Options::                     Options that are available for ERC.

@end detailmenu
@end menu

@node Introduction
@chapter Introduction

ERC is a powerful, modular, and extensible IRC client for Emacs.
It has been included in Emacs since 2006 (@pxref{History}) and is also
available on GNU ELPA.

IRC is short for Internet Relay Chat.  When using IRC, you can
communicate with other users on the same IRC network.  There are many
different networks---if you search for ``IRC networks'' in your
favorite search engine, you will find up-to-date lists of IRC networks
catering to various interests and topics.

To use IRC, you need an IRC client such as ERC.  Using the client, you
connect to an IRC server.  Once you've done that, you will have access
to all available channels on that server's network.  A channel is
basically a chat room, and what you type in a channel will be shown to
all other users in that channel.  You can be in several channels at
the same time---ERC will show each channel in its own buffer.

IRC channel names always begin with a @samp{#} character.  For
example, the Emacs channel on Libera.Chat is @samp{#emacs}, and the
ERC channel is @samp{#erc}.  Do not confuse them with the hashtags
used on many social media platforms.

You can also send private messages to other IRC users on the same
network, even if they are not in the same channels as you.

ERC comes with the following capabilities enabled by default.

@itemize @bullet
@item Flood control
@item Timestamps
@item Join channels automatically
@item Buttonize URLs, nicknames, and other text
@item Wrap long lines
@item Highlight or remove IRC control characters
@item Highlight pals, fools, and other keywords
@item Detect netsplits
@item Complete nicknames and commands in a programmable fashion
@item Make displayed lines read-only
@item Input history
@item Track channel activity in the mode-line

@end itemize


@node Getting Started
@chapter Getting Started
@cindex settings

The command @kbd{M-x erc} will start ERC and prompt for the server to
connect to.  If you're unsure of which server or network to connect
to, we suggest starting with ``irc.libera.chat''.  There you will find
the @samp{#emacs} channels where you can chat with other Emacs users,
and if you're having trouble with ERC, you can join the @samp{#erc}
channel and ask for help there.

At some point in your ERC journey, you'll inevitably want to change
how the client looks and behaves.  As with other Emacs applications,
the typical place to store your settings is your @file{init.el}.  If
you would rather use the Customize interface, a good place to start is
by running @kbd{M-x customize-group @key{RET} erc @key{RET}}.  In
particular, ERC comes with lots of modules that may be enabled or
disabled; to select which ones you want, do @kbd{M-x
customize-variable @key{RET} erc-modules @key{RET}}.

@menu
* Sample Session::              Example of connecting to the #emacs channel
* Special Features::            Differences from standalone IRC clients
@end menu

@node Sample Session
@section Sample Session

This example ERC session describes how to connect to the @samp{#emacs}
channel on Libera.Chat.  Also worth checking out is Libera's own
introductory guide to IRC, @uref{https://libera.chat/guides/basics},
which presents a more comprehensive overview without instructions
specific to ERC.

@itemize @bullet

@item Connect to Libera.Chat

Run @kbd{M-x erc @key{RET}}.  Use @samp{irc.libera.chat} for the
server and @samp{6667} for the port.  Choose a nickname, and hit
@key{y} when asked if you'd prefer to connect over @acronym{TLS}.

@item Get used to the interface

Switch to the @file{Libera.Chat} buffer if you're not already there.
ERC calls this a @dfn{server buffer}, and it must exist for the
duration of the session.  You will likely see some messages about
``ident'', authentication, and the like, followed by information
describing the current server and the network.

@item Join the #emacs channel

In the server buffer, type @kbd{/join #emacs @key{RET}} at the prompt.
ERC will create a new buffer called @file{#emacs}.  If you've already
configured ERC, you may need to switch to it manually.  Once there,
you will see the channel's ``topic'' in the buffer's header line
(@pxref{Header Lines,,,elisp,}) and a list of people currently in the
channel.  If you can't see the full topic, mouse over it or type
@kbd{/topic @key{RET}} at the prompt.

@item Register your nickname with Libera.Chat

In order to access essential network features, like speaking in
certain channels and participating in private conversations, you'll
likely have to ``register'' your nickname.  To do so, switch to the
@file{Libera.Chat} buffer and type @kbd{/msg NickServ register
@samp{<password>} @samp{<email>} @key{RET}}, replacing
@samp{<password>} and @samp{<email>} with your desired account
password and contact email (both sans quotes).  The server should tell
you that the operation was successful.  See the official Libera.Chat
docs if you encounter problems.

In addition to creating an account, this process also
``authenticates'' you to the network's ``account services'' system for
the duration of the session.  In other words, you're now logged in.
However, when you connect in the future, you'll need to authenticate
again by providing the same credentials somehow.  When you're finished
with this walk through, see ``Next Steps'', below, to learn some ways
to do that.

@item Talk to people in the channel

Switch back to the @file{#emacs} buffer and type a message at the
prompt, hitting @kbd{RET} once satisfied.  Everyone in the channel
will now see your message.

@item Open a query buffer to talk to someone

If you want to talk with someone in private, type @kbd{/query
@samp{<nick>} @key{RET}}, replacing @samp{<nick>} with the their
nickname.  As before, with the server buffer, if this new @dfn{query
buffer} doesn't appear in the current window, you may have to switch
to it.  Regardless, its name should match @samp{<nick>}.  Once there,
type something at the prompt and hit @kbd{RET}, and the other party
will see it.

Keep in mind that if either party isn't authenticated, you may not be
able to converse at all.  Also, depending on the network, certain
social conventions may apply to the practice of direct messaging.  As
a general rule, queries should usually be reserved for personal
matters rather than technical help, which can often benefit (and
benefit @emph{from}) a larger audience.

@item Next steps

Try joining another channel, such as @samp{#erc}, where ERC users and
developers hang out (@pxref{Official IRC channels} for more on the
history of @samp{#emacs}).  For ideas on various options to customize,
@pxref{Sample Configuration}.  To learn how ERC can authenticate you
to the network automatically whenever you connect, @pxref{SASL}.  As
always, if you encounter problems, @pxref{Getting Help and Reporting
Bugs}.

@end itemize

@node Special Features
@section Special Features

ERC has some features that distinguish it from some IRC clients.

@itemize @bullet

@item multiple channels and multiple servers

Every channel is put in a separate buffer.  Several IRC servers may be
connected to at the same time.

@cindex query buffers
@item private message separation

Private conversations are treated as channels, and are put into separate
buffers in Emacs.  We call these ``query buffers''.

@item highlighting

Some occurrences of words can be highlighted, which makes it easier to
track different kinds of conversations.

@item notification

ERC can notify you that certain users are online.

@item channel tracking

Channels can be hidden and conversation continue in the background.  You
are notified when something is said in such a channel that is not
currently visible.  This makes it easy to get Real Work done while still
maintaining an IRC presence.

@item nick completion

ERC can complete words upon hitting @kbd{TAB}, which eases the writing
of nicknames in messages.

@cindex history ring
@item history

Past actions are kept in history rings for future use.  To navigate a
history ring, hit @kbd{M-p} to go backwards and @kbd{M-n} to go
forwards.

@item multiple languages

Different channels and servers may have different language encodings.

multiple languages.  Please contact the Emacs developers
if you are interested in helping with the
translation effort.

@item user scripting

Users can load scripts (e.g., auto greeting scripts) when ERC starts up.

It is also possible to make custom IRC commands, if you know a little
Emacs Lisp.  Just make an Emacs Lisp function and call it
@code{erc-cmd-NEWCOMMAND}, where @code{NEWCOMMAND} is the name of the
new command in capital letters.

@item auto reconnect

If the connection goes away at some point, ERC will try to reconnect
automatically.  If it fails to reconnect, and you want to try to
manually reestablish the connection at some later point, switch to an
ERC buffer and run the @code{/RECONNECT} command.

@end itemize


@node Keystroke Summary
@chapter Keys Used in ERC
@cindex keystrokes

This is a summary of keystrokes available in every ERC buffer.

@table @kbd

@item C-a or <home> (@code{erc-bol})
Go to beginning of line or end of prompt.

@item @key{RET} (@code{erc-send-current-line})
Send the current line

@item @key{TAB} (@code{completion-at-point} or @code{erc-button-next})
If at prompt, complete the current word.
Otherwise, move to the next link or button.

@item M-@key{TAB} (@code{ispell-complete-word})
Complete the given word, using ispell.

@item C-c C-a (@code{erc-bol})
Go to beginning of line or end of prompt.

@item C-c C-b (@code{erc-switch-to-buffer})
Use @code{read-buffer} to prompt for a ERC buffer to switch to.

@item C-c C-c (@code{erc-toggle-interpret-controls})
Toggle interpretation of control sequences in messages.

@item C-c C-d (@code{erc-input-action})
Interactively input a user action and send it to IRC.

@item C-c C-e (@code{erc-toggle-ctcp-autoresponse})
Toggle automatic CTCP replies (like VERSION and PING).

@item C-c C-f (@code{erc-toggle-flood-control})
Toggle use of flood control on sent messages.

@item C-c @key{TAB} (@code{erc-invite-only-mode})
Turn on the invite only mode (+i) for the current channel.

@item C-c C-j (@code{erc-join-channel})
Join channel.  If point is at the beginning of a channel name, use that
as default.

@item C-c C-k (@code{erc-go-to-log-matches-buffer})
Interactively open an erc-log-matches buffer

@item C-c C-l (@code{erc-save-buffer-in-logs})
Append buffer contents to the log file, if logging is enabled.

@item C-c C-n (@code{erc-channel-names})
Run "/names #channel" in the current channel.

@item C-c C-o (@code{erc-get-channel-mode-from-keypress})
Read a key sequence and call the corresponding channel mode function.
After doing @kbd{C-c C-o}, type in a channel mode letter.

@kbd{C-g} means quit.
@kbd{RET} lets you type more than one mode at a time.
If @kbd{l} is pressed, @code{erc-set-channel-limit} gets called.
If @kbd{k} is pressed, @code{erc-set-channel-key} gets called.
Anything else will be sent to @code{erc-toggle-channel-mode}.

@item C-c C-p (@code{erc-part-from-channel})
Part from the current channel and prompt for a reason.

@item C-c C-q (@code{erc-quit-server})
Disconnect from current server after prompting for reason.

@item C-c C-r (@code{erc-remove-text-properties-region})
Clears the region (start,end) in object from all colors, etc.

@item C-c C-t (@code{erc-set-topic})
Prompt for a topic for the current channel.

@item C-c C-u (@code{erc-kill-input})
Kill current input line using @code{erc-bol} followed by @code{kill-line}.

@end table


@node Modules
@chapter Modules
@cindex modules

One way to add functionality to ERC is to customize which of its many
modules are loaded.

You can do this by typing @kbd{C-h v erc-modules @key{RET}} and clicking
@samp{customize} near the bottom of the resulting help buffer, where it
says ``You can @emph{customize} this variable.''  When
removing a module outside of Customize, you may wish to ensure it's
disabled by invoking its associated minor-mode toggle with a
nonpositive prefix argument, for example, @kbd{C-u - M-x
erc-spelling-mode @key{RET}}.  Additionally, if you plan on loading
third-party modules that perform atypical setup on activation, you may
need to arrange for calling @code{erc-update-modules} in your init
file.  Examples of such setup might include registering an
@code{erc-before-connect} hook, advising @code{erc-open}, and
modifying @code{erc-modules} itself.  On Emacs 29 and greater, you can
also run @code{erc-update-modules} indirectly, via @code{(setopt
erc-modules erc-modules)}.

The following is a list of available modules.

@table @code

@cindex modules, autoaway
@item autoaway
Set away status automatically

@cindex modules, autojoin
@item autojoin
Join channels automatically

@cindex modules, bufbar
@item bufbar
List buffers belonging to a connection in a side window; part of
Custom group @code{erc-status-sidebar}

@cindex modules, button
@item button
Buttonize URLs, nicknames, and other text

@cindex modules, capab-identify
@item capab-identify
Mark unidentified users on freenode and other servers supporting CAPAB.

@cindex modules, command-indicator
@item command-indicator
Echo command lines for ``slash commands'', like @kbd{/JOIN #erc} and
@kbd{/HELP join}

@cindex modules, completion
@cindex modules, pcomplete
@item completion (aka pcomplete)
Complete nicknames and commands (programmable)

@cindex modules, fill
@item fill
Wrap long lines

@cindex modules, identd
@item identd
Launch an identd server on port 8113

@cindex modules, irccontrols
@item irccontrols
Highlight or remove IRC control characters

@cindex modules, keep-place
@item keep-place
Remember your position in buffers

@cindex modules, log
@item log
Save buffers in logs

@cindex modules, match
@item match
Highlight pals, fools, and other keywords

@cindex modules, menu
@item menu
Display a menu in ERC buffers

@cindex modules, netsplit
@item netsplit
Detect netsplits

@cindex modules, nicks
@item nicks
Automatically colorize nicks

@cindex modules, nickbar
@item nickbar
List participating nicks for the current target buffer in a side
window; part of Custom group @code{erc-speedbar}

@cindex modules, noncommands
@item noncommands
Don't display non-IRC commands after evaluation

@cindex modules, notify
@item notify
Notify when the online status of certain users changes

@cindex modules, notifications
@item notifications
Send you a notification when you get a private message,
or your nickname is mentioned

@cindex modules, page
@item page
Process CTCP PAGE requests from IRC

@cindex modules, querypoll
@item querypoll
Update query participant data by continually polling the server

@cindex modules, readonly
@item readonly
Make displayed lines read-only

@cindex modules, replace
@item replace
Replace text in messages

@cindex modules, ring
@item ring
Enable an input history

@cindex modules, sasl
@item sasl
Enable SASL authentication

@cindex modules, scrolltobottom
@item scrolltobottom
Scroll to the bottom of the buffer

@cindex modules, services
@item services
Identify to Nickserv (IRC Services) automatically

@cindex modules, smiley
@item smiley
Convert smileys to pretty icons

@cindex modules, sound
@item sound
Play sounds when you receive CTCP SOUND requests

@cindex modules, spelling
@item spelling
Check spelling of messages

@cindex modules, stamp
@item stamp
Add timestamps to messages

@cindex modules, track
@item track
Track channel activity in the mode-line

@cindex modules, truncate
@item truncate
Truncate buffers to a certain size

@cindex modules, unmorse
@item unmorse
Translate morse code in messages

@end table

@anchor{Auxiliary Modules}
@subheading Auxiliary Modules
@cindex auxiliary modules

For various reasons, the following modules aren't currently listed in
the Custom interface for @code{erc-modules}, but feel free to add them
explicitly.  They may be managed by another module or considered more
useful when toggled interactively or just deemed experimental.

@table @code

@cindex modules, fill-wrap
@item fill-wrap
Wrap long lines using @code{visual-line-mode}

@cindex modules, keep-place-indicator
@item keep-place-indicator
Remember your place in buffers with a visible reminder; activated
interactively or via something like @code{erc-join-hook}

@cindex modules, services-regain
@item services-regain
Automatically ask NickServ to reclaim your nick when reconnecting;
experimental as of ERC 5.6

@end table

@anchor{Required Modules}
@subheading Required Modules
@cindex required modules

Note that some modules are essential to core IRC operations and thus
not listed above.  You can nevertheless still remove these, but doing
so demands special precautions to avoid degrading the user experience.
At present, the only such module is @code{networks}, whose library ERC
always loads anyway.

@anchor{Local Modules}
@subheading Local Modules
@cindex local modules

All modules operate as minor modes under the hood, and some newer ones
may be defined as buffer-local.  These so-called ``local modules'' are
a work in progress and their behavior and interface are subject to
change.  As of ERC 5.5, the only practical differences are as follows:

@enumerate
@item
``Control variables,'' like @code{erc-sasl-mode}, retain their values
across IRC sessions and override @code{erc-module} membership when
influencing module activation.
@item
Removing a local module from @code{erc-modules} via Customize not only
disables its mode but also kills its control variable in all ERC
buffers.
@item
``Mode toggles,'' like @code{erc-sasl-mode} and the complementary
@code{erc-sasl-enable}/@code{erc-sasl-disable} pairing, behave
differently than their global counterparts.
@end enumerate

In target buffers, a local module's activation state survives
``reassociation'' by default, but modules themselves always have the
final say.  For example, a module may reset all instances of itself in
its network context upon reconnecting.  Moreover, the value of a mode
variable may be meaningless in buffers that its module has no interest
in.  For example, the value of @code{erc-sasl-mode} doesn't matter in
target buffers and may even remain non-@code{nil} after SASL has been
disabled for the current connection (and vice versa).

When it comes to server buffers, a module's activation state only
persists for sessions revived via the automatic reconnection mechanism
or a manual @samp{/reconnect} issued at the prompt.  In other words,
this doesn't apply to sessions revived by an entry-point command, such
as @code{erc-tls}, because such commands always ensure a clean slate
by looking only to @code{erc-modules}.  Although a session revived in
this manner may indeed harvest other information from a previous
server buffer, it simply doesn't care which modules might have been
active during that connection.

Lastly, a local mode's toggle command, like @code{erc-sasl-mode}, only
affects the current buffer, but its ``non-mode'' cousins, like
@code{erc-sasl-enable} and @code{erc-sasl-disable}, operate on all
buffers belonging to their connection (when called interactively).
And unlike global toggles, none of these ever mutates
@code{erc-modules}.

@c PRE5_4: Document every option of every module in its own subnode


@node Advanced Usage
@chapter Advanced Usage
@cindex advanced topics

@menu
* Connecting::                  Ways of connecting to an IRC server.
* SASL::                        Authenticating via SASL.
* Sample Configuration::        An example configuration file.
* Integrations::                Integrations available for ERC.
* Module Loading::              How ERC loads modules.
* Match API::                   Custom matching and highlighting.
* Options::                     Options that are available for ERC.

@detailmenu
--- Detailed Node Listing ---

Integrations

* URL::                         Opening IRC URLs in ERC.
* SOCKS::                       Connecting to IRC with a SOCKS proxy.
* auth-source::                 Retrieving auth-source entries with ERC.
* display-buffer::              Controlling how ERC displays buffers.

@end detailmenu
@end menu

@node Connecting
@section Connecting to an IRC Server
@cindex connecting

The easiest way to connect to an IRC server is to call @kbd{M-x erc}.
If you want to assign this function to a keystroke, the following will
help you figure out its parameters.

@defun erc
Select connection parameters and run ERC@.
Non-interactively, it takes the following keyword arguments.

@itemize @bullet
@item @var{server}
@item @var{port}
@item @var{nick}
@item @var{user}
@item @var{password}
@item @var{full-name}
@item @var{id}
@end itemize

For example, calling the command like so

@example lisp
(erc :server "irc.libera.chat" :full-name "J. Random Hacker")
@end example

@noindent
sets @var{server} and @var{full-name} directly while leaving the rest
up to functions like @code{erc-compute-port}.  Note that some
arguments can't be specified interactively.  @var{id}, in particular,
is rarely needed (@pxref{Network Identifier}).

@end defun

@noindent
To connect securely over an encrypted TLS connection, use @kbd{M-x
erc-tls}.

@defun erc-tls
Select connection parameters and run ERC over TLS@.
Non-interactively, it takes the following keyword arguments.

@itemize @bullet
@item @var{server}
@item @var{port}
@item @var{nick}
@item @var{user}
@item @var{password}
@item @var{full-name}
@item @var{id}
@item @var{client-certificate}
@end itemize

That is, if called in the following manner

@example lisp
(erc-tls :server "irc.libera.chat" :full-name "J. Random Hacker")
@end example

@noindent
the command will set @var{server} and @var{full-name} accordingly,
while helpers, like @code{erc-compute-nick}, will determine other
parameters, and some, like @code{client-certificate}, will just be
@code{nil}.

@anchor{client-certificate}
To use a certificate with @code{erc-tls}, specify the optional
@var{client-certificate} keyword argument, whose value should be as
described in the documentation of @code{open-network-stream}: if
non-@code{nil}, it should either be a list where the first element is
the file name of the private key corresponding to a client certificate
and the second element is the file name of the client certificate
itself to use when connecting over TLS, or @code{t}, which means that
@code{auth-source} will be queried for the private key and the
certificate.  Authenticating using a TLS client certificate is also
referred to as ``CertFP'' (Certificate Fingerprint) authentication by
various IRC networks.

Examples of use:

@example
(erc-tls :server "irc.libera.chat" :port 6697
         :client-certificate
         '("/home/bandali/my-cert.key"
           "/home/bandali/my-cert.crt"))
@end example

@example
(erc-tls :server "irc.libera.chat" :port 6697
         :client-certificate
         `(,(expand-file-name "~/cert-libera.key")
           ,(expand-file-name "~/cert-libera.crt")))
@end example

@example
(erc-tls :server "irc.libera.chat" :port 6697
         :client-certificate t)
@end example

In the case of @code{:client-certificate t}, you will need to add a
line like the following to your authinfo file
(e.g. @file{~/.authinfo.gpg}):

@example
machine irc.libera.chat key /home/bandali/my-cert.key cert /home/bandali/my-cert.crt
@end example

@xref{Help for users,,,auth, Emacs auth-source Library}, for more on the
@file{.authinfo}/@file{.netrc} backend of @code{auth-source}.
For other uses of auth-source throughout ERC, @pxref{auth-source,
ERC's auth-source integration}.
@end defun

@subheading Server

@defun erc-compute-server &optional server
Return an IRC server name.

This tries a progressively greater number of default methods until a
non-@code{nil} value is found.

@itemize @bullet
@item @var{server} (the argument passed to this function)
@item The @code{erc-server} option
@item The value of the IRCSERVER environment variable
@item The @code{erc-default-server} variable
@end itemize

@end defun

@defopt erc-server
IRC server to use if one is not provided.
@end defopt

@subheading Port

@defun erc-compute-port &optional port
Return a port for an IRC server.

This tries a progressively greater number of default methods until a
non-@code{nil} value is found.

@itemize @bullet
@item @var{port} (the argument passed to this function)
@item The @code{erc-port} option
@item The @code{erc-default-port} variable
@end itemize

@end defun

@defopt erc-port
IRC port to use if not specified.

This can be either a string or a number.
@end defopt

@subheading Nick

@defun erc-compute-nick &optional nick
Return user's IRC nick.

This tries a progressively greater number of default methods until a
non-@code{nil} value is found.

@itemize
@item @var{nick} (the argument passed to this function)
@item The @code{erc-nick} option
@item The value of the IRCNICK environment variable
@item The result from the @code{user-login-name} function
@end itemize

@end defun

@defopt erc-nick
Nickname to use if one is not provided.

This can be either a string, or a list of strings.
In the latter case, if the first nick in the list is already in use,
other nicks are tried in the list order.
@end defopt

@defopt erc-show-speaker-membership-status
A boolean for including a channel member's @dfn{status prefix} in
their display name when they speak.
@end defopt

@defopt erc-nick-uniquifier
The string to append to the nick if it is already in use.
@end defopt

@defopt erc-try-new-nick-p
If the nickname you chose isn't available, and this option is non-@code{nil},
ERC should automatically attempt to connect with another nickname.

You can manually set another nickname with the /NICK command.
@end defopt

@anchor{username parameter}
@subheading User
@cindex username parameter

@defun erc-compute-user &optional user
Determine a suitable value to send as the first argument of the
opening @samp{USER} IRC command by consulting the following sources:

@itemize
@item
@var{user}, the argument passed to this function
@item
The option @code{erc-email-userid}, assuming @code{erc-anonymous-login}
is non-@code{nil}
@item
The result of calling the function @code{user-login-name}
@end itemize

@end defun

@defopt erc-email-userid
A permanent username value to send for all connections.  It should be
a string abiding by the rules of the network.
@end defopt

@anchor{password parameter}
@anchor{server password}
@cindex password, server
@subheading Password

This parameter was traditionally meant to specify a @dfn{server
password} to be sent along with the IRC @samp{PASS} command.  However,
such passwords aren't widely used.  Instead, networks typically expect
them, when present, to convey other authentication information.  In
the case of account-services (a.k.a., ``NickServ'') credentials, this
typically involves a special syntax, such as @samp{myuser:mypass}.
IRC bouncers often do something similar but include a pre-configured
network-ID component, for example, @samp{bncuser/mynet:bncpass}.

In general, if you have @emph{not} been asked by your network or
bouncer to specify a repurposed server password, you should instead
consider setting up @samp{services} or, preferably, @samp{sasl}, both
ERC modules (@pxref{Modules}).  In addition to performing
network-account authentication, these obviate the need for this
parameter completely, although both can optionally borrow it for their
own purposes.  (@xref{SASL, SASL in ERC}.)

@defopt erc-prompt-for-password
If non-@code{nil} (the default), @kbd{M-x erc} and @kbd{M-x erc-tls}
prompt for a server password.  This only affects interactive
invocations of @code{erc} and @code{erc-tls}.
@end defopt

@noindent
If you prefer, you can set this option to @code{nil} and use the
auth-source facility to retrieve a server password, although hitting
@kbd{RET} at the prompt may achieve the same effect.
@xref{auth-source, ERC's auth-source integration}, for more.

@subheading Full name

@defun erc-compute-full-name &optional full-name
Return user's full name.

This tries a progressively greater number of default methods until a
non-@code{nil} value is found.

@itemize @bullet
@item
@var{full-name} (the argument passed to this function)
@item
The @code{erc-user-full-name} option
@item
The value of the IRCNAME environment variable
@item
The result from the @code{user-full-name} function
@end itemize

@end defun

@defopt erc-user-full-name
User full name.

This can be either a string or a function to call.
@end defopt


@anchor{Network Identifier}
@subheading ID

ERC uses an abstract designation, called @dfn{network context
identifier}, for referring to a connection internally.  While normally
derived from a combination of logical and physical connection
parameters, an ID can also be explicitly provided via an entry-point
command (like @code{erc-tls}).  Use this in rare situations where ERC
would otherwise have trouble discerning between connections.

One such situation might arise when using multiple connections to the
same network with the same nick but different (nonstandard) @samp{device}
identifiers, which some bouncers may support.  Another might be when
mimicking the experience offered by popular standalone clients, which
normally offer ``named'' persistent configurations with server buffers
reflecting those names.  Yet another use case might involve
third-party code needing to identify a connection unequivocally, but in
a human-friendly way suitable for UI components.

When providing an ID as an entry-point argument, strings and symbols
make the most sense, but any reasonably printable object is
acceptable.

@node SASL
@section Authenticating via SASL
@cindex SASL

If you've used @acronym{SASL} elsewhere, you can probably skip to the
examples below.  Otherwise, if you haven't already registered with
your network, please do so now, referring to the network's own
instructions for details.  If you're new to IRC and using a bouncer,
know that you probably won't be needing this for the client-to-bouncer
connection.

When you're ready to get started, add @code{sasl} to
@code{erc-modules}, like you would any other module.  If unsure which
@dfn{mechanism} to choose, stick with the default of @samp{PLAIN}.
Then try @kbd{C-u M-x erc-tls @key{RET}}, and give your account name
for the @samp{user} parameter and your account password for the
@samp{server password}.

@defopt erc-sasl-mechanism
The name of an SASL subprotocol type as a @emph{lowercase} symbol.
The value can be one of the following:

@table @asis
@item @code{plain} or @code{scram} (``password-based'')
Here, ``password'' refers to your account password, which is usually
your @samp{NickServ} password.  To make this work, customize
@code{erc-sasl-user} and @code{erc-sasl-password} or specify the
@code{:user} and @code{:password} keyword arguments when invoking
@code{erc-tls}.

@item @code{external} (via client @acronym{TLS} certificate)
This works in conjunction with the @code{:client-certificate} keyword
offered by @code{erc-tls}.  Just ensure you've registered your
fingerprint with the network beforehand.  The fingerprint is usually a
SHA1 or SHA256 digest in either "normalized" or "openssl" forms.  The
first is lowercase without delims (@samp{deadbeef}) and the second
uppercase with colon seps (@samp{DE:AD:BE:EF}).  These days, there's
usually a @samp{CERT ADD} command offered by NickServ that can
register you automatically if you issue it while connected with a
client cert.  @xref{client-certificate}.

Additional considerations:
@enumerate
@item
Most IRCds will allow you to authenticate with a client cert but
without the hassle of SASL (meaning you may not need this module).
@item
Technically, @var{EXTERNAL} merely indicates that an out-of-band mode
of authentication is in effect (being deferred to), so depending on
the specific application or service, there's a remote chance your
server has something else in mind.
@end enumerate

@item @code{ecdsa-nist256p-challenge}
This mechanism is quite complicated and currently requires the
external @samp{openssl} executable, so please use something else if at
all possible.  Ignoring that, specify your key file (e.g.,
@samp{~/pki/mykey.pem}) as the value of @code{erc-sasl-password}, and
then configure your network settings.  On servers running Atheme
services, you can add your public key with @samp{NickServ} like so:

@example
ERC> /msg NickServ set property \
     pubkey AgGZmlYTUjJlea/BVz7yrjJ6gysiAPaQxzeUzTH4hd5j

@end example
(You may be able to omit the @samp{property} subcommand.)
@end table

@end defopt

@defopt erc-sasl-user
This should be your network account username, typically the same one
registered with nickname services.  Specify this when your NickServ
login differs from the @code{:user} you're connecting with.
@xref{username parameter}.
@end defopt

@defopt erc-sasl-password
As noted elsewhere, the entry-point @code{:password} param was
originally intended for traditional ``server passwords,'' but these
aren't really used any more (@pxref{password parameter}).  As such,
this option defaults to borrowing that parameter for its own uses,
thus allowing you to call @code{erc-tls} with @code{:password} set to
your NickServ password.

You can also set this to a nonemtpy string, and ERC will send that
when needed, no questions asked.  Or, if you'd rather use auth-source,
set @code{erc-sasl-auth-source-function} to a function, and ERC will
perform an auth-source query instead.  In all cases, ERC will prompt
you for input as a last resort.

Lastly, if your mechanism is @code{ecdsa-nist256p-challenge}, this
option should instead hold the file name of your key.
@end defopt

@anchor{SASL auth-source function}
@defopt erc-sasl-auth-source-function
This is nearly identical to the other ERC @samp{auth-source} function
options (@pxref{auth-source functions}) except that the default value
here is @code{nil}, meaning you have to set it to something like
@code{erc-auth-source-search} for queries to be performed.  For
convenience, this module provides the following as a possible value:

@defun erc-sasl-auth-source-password-as-host &rest plist
Setting @code{erc-sasl-auth-source-function} to this function tells
ERC to use @code{erc-sasl-password} for the @code{:host} field when
querying auth-source, even if its value is the default
@code{:password}, in which case ERC knows to ``resolve'' it to
@code{erc-session-password} and use that as long as it's
non-@code{nil}.  Otherwise, ERC just defers to
@code{erc-auth-source-search} to determine the @code{:host}, along
with everything else.
@end defun

As long as this option specifies a function, ERC will pass it the
``resolved'' value of @code{erc-sasl-user} for the auth-source
@code{:user} param.
@end defopt

@defopt erc-sasl-authzid
In the rarest of circumstances, a network may want you to specify a
specific role or assume an alternate identity.  In most cases, this
happens because the server is buggy or misconfigured.  If you suspect
such a thing, please contact your network operator.  Otherwise, just
leave this set to @code{nil}.
@end defopt

@subheading Examples

@itemize @bullet
@item
Defaults

@lisp
(erc-tls :server "irc.libera.chat" :port 6697
         :nick "aph"
         :user "APHacker"
         :password "changeme")
@end lisp

Here, after adding @code{sasl} to @code{erc-modules} via the Customize
interface, you authenticate to Libera.Chat using the @samp{PLAIN}
mechanism and your NickServ credentials, @samp{APHacker} and
@samp{changeme}.

@item
External

@lisp
(setopt erc-sasl-mechanism 'external)

(erc-tls :server "irc.libera.chat" :port 6697 :nick "aph"
         :client-certificate
         '("/home/aph/my.key" "/home/aph/my.crt"))
@end lisp

You decide to switch things up and try out the @samp{EXTERNAL}
mechanism.  You follow your network's instructions for telling
NickServ about your client-certificate's fingerprint, and you
authenticate successfully.

@item
Multiple networks

@example
# ~/.authinfo.gpg

machine irc.libera.chat key /home/aph/my.key cert /home/aph/my.crt
machine Example.Net login alyssa password sEcReT
machine Example.Net login aph-bot password sesame
@end example

@lisp
;; init.el

(defun my-erc-up (network)
  (interactive "Snetwork: ")
  (require 'erc-sasl)
  (or (let ((erc-modules (cons 'sasl erc-modules)))
        (pcase network
          ('libera
           (let ((erc-sasl-mechanism 'external))
             (erc-tls :server "irc.libera.chat"
                      :client-certificate t)))
          ('example
           (let ((erc-sasl-auth-source-function
                  #'erc-sasl-auth-source-password-as-host))
             (erc-tls :server "irc.example.net"
                      :user "alyssa"
                      :password "Example.Net")))))
      ;; Non-SASL
      (call-interactively #'erc-tls)))
@end lisp

You've started storing your credentials with auth-source and have
decided to try SASL on another network as well.  But there's a catch:
this network doesn't support @samp{EXTERNAL}.  You use
@code{let}-binding to work around this and successfully authenticate
to both networks.  (Note that this example assumes you've removed
@code{sasl} from @code{erc-modules} globally and have instead opted to
add it locally when connecting to preconfigured networks.)

@end itemize

@subheading Troubleshooting

First and foremost, please know that ERC's SASL offering is currently
limited by a lack of support for proper IRCv3 capability negotiation.
In most cases, this shouldn't affect your ability to authenticate.

If you're struggling, remember that your SASL password is almost
always your NickServ password.  When in doubt, try restoring all SASL
options to their defaults and calling @code{erc-tls} with @code{:user}
set to your NickServ account name and @code{:password} to your
NickServ password.  If you're still having trouble, please contact us
(@pxref{Getting Help and Reporting Bugs}).

As you try out different settings, keep in mind that it's best to
create a fresh session for every change, for example, by calling
@code{erc-tls} from scratch.  More experienced users may be able to
get away with cycling @code{erc-sasl-mode} and issuing a
@samp{/reconnect}, but that's generally not recommended.  Whatever the
case, you'll probably want to temporarily disable
@code{erc-server-auto-reconnect} while experimenting.

@node Sample Configuration
@section Sample Configuration
@cindex configuration, sample

Here is an example configuration for ERC@.  @strong{Don't panic} if
you aren't familiar with @samp{use-package} or have no interest in
learning it.  For our purposes, it's just a means of presenting
configuration details in a tidy, standardized format.  If it helps,
just pretend it's some make-believe, pseudo configuration language.
And while the syntax below is easy enough to intuit and adapt to your
setup, you may wish to keep the following in mind:

@itemize @bullet
@item
Each @code{use-package} ``declaration'' focuses on a library
``feature'', which is just a symbol you'd normally @code{require} in
your config.

@item
Emacs loads anything in a @code{:config} section @emph{after} loading
whatever library @code{provide}s the declaration's feature.

@item
Everything in a @code{:custom} or @code{:custom-face} section is
basically something you'd find in your @code{custom-file}.

@item
For more info, @pxref{Named Features,,, elisp,}, or @pxref{Top,,,
use-package,}.
@end itemize

@noindent
The following would typically go in your init file.  Experienced users
may opt to keep any non-settings, like commands and functions, in a
dedicated @file{~/.emacs.d/.ercrc.el}.  Whatever the case, please keep
in mind that you can replace nearly all of the following with Custom
settings (@pxref{Sample configuration via Customize}).

@lisp
;;; My ERC configuration -*- lexical-binding: t -*-

(use-package erc
  :config
  ;; Prefer SASL to NickServ, colorize nicknames, and show side panels
  ;; with joined channels and members
  (setopt erc-modules
          (seq-union '(sasl nicks bufbar nickbar scrolltobottom)
                     erc-modules))

  :custom
  ;; Protect me from accidentally sending excess lines.
  (erc-inhibit-multiline-input t)
  (erc-send-whitespace-lines t)
  (erc-ask-about-multiline-input t)
  ;; Scroll all windows to prompt when submitting input.
  (erc-scrolltobottom-all t)

  ;; Reconnect automatically using a fancy strategy.
  (erc-server-reconnect-function #'erc-server-delayed-check-reconnect)
  (erc-server-reconnect-timeout 30)

  ;; Show new buffers in the current window instead of a split.
  (erc-interactive-display 'buffer)

  ;; Insert a newline when I hit <RET> at the prompt, and prefer
  ;; something more deliberate for actually sending messages.
  :bind (:map erc-mode-map
              ("RET" . nil)
              ("C-c C-c" . #'erc-send-current-line))

  ;; Emphasize buttonized text in notices.
  :custom-face (erc-notice-face ((t (:slant italic :weight unspecified)))))

(use-package erc-sasl
  ;; Since my account name is the same as my nick, free me from having
  ;; to hit C-u before M-x erc to trigger a username prompt.
  :custom (erc-sasl-user :nick))

(use-package erc-join
  ;; Join #emacs and #erc whenever I connect to Libera.Chat.
  :custom (erc-autojoin-channels-alist '((Libera.Chat "#emacs" "#erc"))))

(use-package erc-fill
  :custom
  ;; Prefer one message per line without continuation indicators.
  (erc-fill-function #'erc-fill-wrap)
  (erc-fill-static-center 18)

  :bind (:map erc-fill-wrap-mode-map ("C-c =" . #'erc-fill-wrap-nudge)))

(use-package erc-match
  ;; Use the same face for my own nick wherever it appears.
  :custom-face
  (erc-current-nick-face ((t ( :weight unspecified
                               :foreground unspecified
                               :inherit erc-my-nick-face)))))

(use-package erc-track
  ;; Prevent JOINs and PARTs from lighting up the mode-line.
  :config (setopt erc-track-faces-priority-list
                  (remq 'erc-notice-face erc-track-faces-priority-list))

  :custom (erc-track-priority-faces-only 'all))

(use-package erc-goodies
  ;; Turn on read indicators when joining channels.
  :hook (erc-join . my-erc-enable-keep-place-indicator-on-join))

(defvar my-erc-read-indicator-channels '("#emacs")
  "Channels in which to show a `keep-place-indicator'.")

(defun my-erc-enable-keep-place-indicator-on-join ()
  "Enable read indicators for certain queries or channels."
  (when (member (erc-default-target) my-erc-read-indicator-channels)
    (erc-keep-place-indicator-mode +1)))

;; Handy commands from the Emacs Wiki.
(defun erc-cmd-TRACK (&optional target)
  "Start tracking TARGET or that of current buffer."
  (setq erc-track-exclude
        (delete (or target (erc-default-target) (current-buffer))
                erc-track-exclude)))

(defun erc-cmd-UNTRACK (&optional target)
  "Stop tracking TARGET or that of current buffer."
  (setq erc-track-exclude
        (cl-pushnew (or target (erc-default-target) (current-buffer))
                    erc-track-exclude
                    :test #'equal)))

@end lisp

@noindent
Those familiar with @code{use-package} may have noticed the lack of
@code{:defer} keyword args.  This was done to conserve space, but you
can just pretend that this user has enabled
@code{use-package-always-defer} elsewhere.

@anchor{Sample configuration via Customize}
@subheading Via Customize
@cindex configuration, via customize

As mentioned, Customize users can accomplish nearly all of the above
via the Customize interface.  Start by running @kbd{M-x
customize-group @key{RET} erc @key{RET}}, and search for ``Modules''
with @kbd{C-s modules @key{RET}}.  Toggle open the flyout menu to
reveal the full @dfn{widget} panel, a web-form-like interface for
``Erc Modules''.  Tick the boxes for @samp{bufbar}, @samp{nickbar},
@samp{nicks}, @samp{sasl}, and @samp{scrolltobottom}.

Next, search for the phrases ``Erc Ask About Multiline Input'', ``Erc
Inhibit Multiline Input'', and ``Erc Send Whitespace Lines''.  These
are the print names of three boolean options that control how ERC
treats prompt input containing line breaks.  When visiting each
option's section, twirl open its triangle icon to reveal its widget
UI, and click its @samp{[Toggle]} button to set its value to @code{t}.
While going about this, you may find it helpful to glance at the
descriptions just in case you want to disable them later.  When
finished, hit @kbd{C-x C-s} or click @samp{[Apply and Save]} atop the
buffer.

Now do the same for another couple options, this time having to do
with automatic reconnection.  But instead of searching for their print
names, try running @kbd{M-x customize-option @key{RET} @samp{<option>}
@key{RET}}, replacing @samp{<option>} with:

@itemize @bullet
@item @code{erc-server-reconnect-function}, a function
@item @code{erc-server-reconnect-timeout}, a number
@end itemize

@noindent
(If it helps, hit @key{TAB} for completion.)  As you may have noticed,
when customizing options individually, each buffer displays but a
single option's widget.  When you get to the buffer for ``Erc Server
Reconnect Function'', you'll see that @samp{[Toggle]} has been
replaced with @samp{[Value Menu]} and that clicking it reveals three
choices in a pop-up window.  Enter @kbd{1} to select
@code{erc-server-delayed-check-reconnect} before @key{TAB}'ing over to
@samp{[State]} and hitting @key{RET}.  Enter @kbd{1} again, this time
to persists your changes.

For the final option, @code{erc-server-reconnect-timeout}, you'll
encounter a text field (instead of a button), which works like those
in a typical web form.  Enter @samp{30} and hit @kbd{C-x C-s} to save.
Just for fun, click the group link for @samp{Erc Server} at the bottom
of the buffer.  You could just as well have set the last two options
from this ``custom group'' buffer alone, which very much resembles the
one for the @samp{Erc} group, which is actually the ``parent'' of this
group (note the ``breadcrumb'' for group @samp{Erc} atop the buffer).
Indeed, you can always get back here by running @kbd{M-x
customize-group @key{RET} erc-server @key{RET}} from almost anywhere
in Emacs.

To make sure you've got this, try quickly customizing the option
@code{erc-interactive-display}, which lives in the @samp{Erc Buffers}
group (@kbd{M-x customize-group @key{RET} erc-buffers @key{RET}}).  As
its doc string explains, the option controls where new buffers show up
when you do @kbd{M-x erc-tls @key{RET}} or issue certain @dfn{slash
commands}, like @kbd{/JOIN #emacs-beginners @key{RET}}, at ERC's
prompt.  Change its value to the symbol @code{buffer} by choosing
@samp{Use current window} (item @kbd{5}) from the option's
@samp{[Value Menu]}.  Don't forget to save.

If you need more practice, try enabling the boolean option
@code{erc-scrolltobottom-all}, which lives in the @samp{Erc Display}
group (@kbd{M-x customize-group @key{RET} erc-display @key{RET}}).
When enabled, this option tells the @samp{scrolltobottom} module to
adjust all ERC windows instead of just the one you're currently typing
in.

Now it's time to set some key bindings for @code{erc-mode-map}, a
major-mode keymap active in all ERC buffers.  In general, it's best to
do this part either entirely or in conjunction with some lisp code in
you init file.  However, to keep things ``simple'', we'll do it all in
customization buffers.  To get started, hit @kbd{M-x customize-group
@key{RET} erc-hooks @key{RET}} and search for ``Erc Mode Hook''.  In
the widget form, click @samp{[INS]}, and paste the following into the
value field in place of the default text.

@lisp
(lambda ()
  (keymap-set erc-mode-map "RET" nil)
  (keymap-set erc-mode-map "C-c C-c" 'erc-send-current-line))
@end lisp

@noindent
Don't worry about the line breaks.  Emacs is smart enough to handle
those.  When you're ready, click @samp{[Apply and Save]}.

Next, try tweaking the face ERC uses to stylize server messages that
say things like ``SoAndSo has joined channel #chan''.  Type @kbd{M-x
customize-face @key{RET} erc-notice-face @key{RET}}.  Click the
``link''-looking button at the very bottom that says something like
``Show All Attributes''.  Untick @samp{Weight} and tick @samp{Slant}.
Then, in the latter's @samp{[Value Menu]}, enter @samp{0} for
@samp{italic}.  Hit @kbd{C-x C-s} to save.

Time for some more involved configuring.  From now on, if something
isn't applicable to your setup, just skip ahead.  Also, note that if
you've installed ERC from GNU ELPA, you may need to load libraries for
groups and options you'd like to customize before Emacs can create a
customization buffer.  For example, to do this for the group
@code{erc-sasl}, run @kbd{M-: (require 'erc-sasl) @key{RET}}.

Speaking of @acronym{SASL}, those already authenticating with it may
have noticed that connecting interactively requires running @kbd{C-u
M-x erc-tls @key{RET}} in order to receive a ``User'' prompt for your
account name.  However, if your nickname happens to be the same as
your account name, you can avoid the leading @kbd{C-u} by customizing
the option @code{erc-sasl-user} to the keyword symbol @code{:nick}.
At the time of writing, you'd hit @kbd{2} when prompted by the
option's @samp{[Value menu]}.  Hit @kbd{C-x C-s} to save your changes.

One of ERC's most configured options lives in @file{erc-join}, and it
determines the channels you join upon connecting.  To make it work for
you, customize the option @code{erc-autojoin-channels-alist}.  In the
customization widget, hit @samp{[INS]} to create a new entry.  In the
@samp{Network:} field, type @samp{Libera.Chat}.  Under
@samp{Channels:}, hit @samp{[INS]} again, this time to create a field
to enter a channel name, and enter @samp{#emacs}.  Now, find and click
on the lowermost @samp{[INS]}, and this time enter @samp{#erc} in the
@samp{Name:} field.  Save your changes.

If you're new to ERC, you may not be familiar with the various ways it
can ``fill'' message text by inserting line breaks.  The most modern
fill style is called @code{fill-wrap}, and it's available by
customizing @code{erc-fill-function} to @code{erc-fill-wrap}, which
appears as @samp{Dynamic word-wrap} in the option's @samp{[Value
Menu]}.  After setting this, change the related option
@code{erc-fill-static-center} to the integer @samp{18}.  Save your
changes.  As a bonus exercise, try binding the key @kbd{C-c =} to the
function @code{erc-fill-wrap-nudge} in the minor-mode keymap
@code{erc-fill-wrap-mode-map} (hint: the minor mode's hook is called
@code{erc-fill-wrap-mode-hook}, and it's not a member of any
customization group).

Try customizing another face, this time with inheritance.  ERC's match
module highlights your nick whenever someone mentions you in
conversation.  However, some users don't like that this face differs
from the one in your own messages.  Let's change that.  Type @kbd{M-x
customize-group @key{RET} erc-faces @key{RET}}.  Either search for the
word ``Current'' or type @kbd{M-x customize-face @key{RET}
erc-current-nick-face @key{RET}}.  Untick @samp{Weight} and
@samp{Foreground}, then click the ``Show All Attributes'' button below
them.  Navigate down to the @samp{Inherit} box, tick it, hit
@samp{[INS]}, and type @code{erc-my-nick-face} in the @samp{Face} field.
Hit @kbd{C-x C-s} to save.

ERC users tend to be picky about the mode line.  If you find that
you'd rather not see changes when people join and leave channels,
customize the option @code{erc-track-faces-priority-list}.  When
visiting its customization buffer, you'll notice it's quite busy.
Ignore everything and type @kbd{C-s erc-notice-face @key{RET}}.  Click
the @samp{[DEL]} button at the beginning of the line you end up on,
and save your changes.  Next, customize the related option
@code{erc-track-priority-faces-only} to the @samp{[Value Menu]} choice
@samp{all}.  Once again, save your changes.

Let's say you'd like to enable a @dfn{local module} (ERC's version of
a local minor mode) in a specific channel.  One way to do that is by
running some code to activate the module if the channel's name
matches.  Try that now by customizing the option @code{erc-join-hook}.
Add the following in the value field before saving your changes:

@lisp
(lambda ()
  (require 'erc-goodies)
  (when (equal (erc-default-target) "#emacs")
    (erc-keep-place-indicator-mode +1)))
@end lisp

Lastly, if you really want the two @dfn{slash commands} defined at the
end of the previous section, you can put them in any file listed in
@code{erc-startup-file-list}, such as @file{~/.emacs.d/.ercrc.el}.
Make sure to put @code{(require 'erc-track)} near the top of the file.
These will allow you to type @kbd{/TRACK @key{RET}} and @kbd{/UNTRACK
@key{RET}} in channels and query buffers to tell ERC whether to show
activity from these buffers in the mode line.


@node Integrations
@section Integrations
@cindex integrations

@menu
* auth-source::                 Retrieving auth-source entries with ERC.
* display-buffer::              Controlling how ERC displays buffers.
@end menu

@anchor{URL}
@subsection URL
@cindex URL

For anything to work, you'll want to set @code{url-irc-function} to
@code{url-irc-erc}.  As a rule of thumb, libraries relying directly on
@code{url-retrieve} should be fine out the box from Emacs 29.1 onward.
On older versions of Emacs, you may need to @code{(require 'erc)}
beforehand.  @xref{Retrieving URLs,,, url, URL}.

For other apps and libraries, such as those relying on the
higher-level @code{browse-url}, you'll oftentimes be asked to specify
a pattern, sometimes paired with a function that accepts a string URL
as a first argument.  For example, with EWW, you may need to tack
something like @code{"\\|\\`irc6?s?:"} onto the end of
@code{eww-use-browse-url}.  But with @code{gnus-button-alist}, you'll
need a function as well:

@lisp
  '("\\birc6?s?://[][a-z0-9.,@@_:+%?&/#-]+" 0 t browse-url-irc 0)
@end lisp

@noindent
Users on Emacs 28 and below may need to use @code{browse-url} instead.

@anchor{SOCKS}
@subsection SOCKS
@cindex SOCKS

People wanting to connect to IRC through a @acronym{SOCKS} proxy are
most likely interested in doing so over @acronym{TOR} (The Onion
Router).  If that's @emph{not} you, please adapt these instructions
accordingly.  Otherwise, keep in mind that support for Tor is
experimental and thus insufficient for safeguarding a user's identity
and location, especially in the case of targeted individuals.

ERC's preferred Tor setup works by accessing a local Tor service
through the built-in @file{socks.el} library that ships with Emacs.
Other means of accessing Tor, such as via @command{torsocks}, are not
supported.  Before getting started, check that your Tor service is up
and running.  You can do that with the following command:

@example
curl --proxy socks5h://localhost:9050 https://check.torproject.org | \
  grep 'Congratulations'
@end example

Networks and servers differ in how they expose Tor endpoints.  In all
cases, you'll want to first set the option @code{socks-server} to
something appropriate, like @code{("tor" "127.0.0.1" 9050 5)}.  For
some networks, setting @code{erc-server-connect-function} to
@code{socks-open-network-stream} might be enough.  Others, like
@samp{Libera.Chat}, involve additional setup.  At the time of writing,
connecting to that network requires both @acronym{TLS} and a permitted
@acronym{SASL} mechanism, like @samp{EXTERNAL} (@pxref{SASL}), as
shown in the following example:

@lisp
(require 'erc)
(require 'socks)

(defun my-erc-open-socks-tls-stream (&rest args)
  (let ((socks-username "")
        (socks-password "")
        (socks-server '("tor" "localhost" 9050 5)))
    (apply #'erc-open-socks-tls-stream args)))

(let* ((erc-modules (cons 'sasl erc-modules))
       (erc-sasl-mechanism 'external)
       (erc-server-connect-function #'my-erc-open-socks-tls-stream))
  (erc-tls
   :server "libera75jm6of4wxpxt4aynol3xjmbtxgfyjpu34ss4d7r7q2v5zrpyd.onion"
   :port 6697
   :nick "jrh"
   :user "jrandomhacker"
   :full-name "J. Random Hacker"
   :client-certificate (list "/home/jrh/key.pem" "/home/jrh/cert.pem")))
@end lisp

@noindent
Here, the user-provided @code{my-erc-open-socks-tls-stream} ensures
that the preferred values for @code{socks-server} and friends will be
available when reconnecting.  If you plan on using @acronym{SOCKS}
with ERC exclusively, you can just set those options and variables
globally and bind @code{erc-server-connect-function} to
@code{erc-open-socks-tls-stream} instead.

@node auth-source
@subsection auth-source
@cindex auth-source

You can configure ERC to use the built-in auth-source library for
looking up passwords. @xref{Top,,auth-source, auth, Emacs auth-source
Library}, for general info on setting up various backends, but keep in
mind that some of these may not be compatible.  Those currently
supported are netrc, plstore, json, secrets, and pass.  To get started
with the default backend, netrc, put a line like the following in your
@file{~/.authinfo.gpg} (or any file named in the option
@code{auth-sources}):

@example
machine irc.example.net login mynick password sEcReT
@end example

@anchor{auth-source Server Password}
@subsubheading Server Passwords
When retrieving passwords to accompany the IRC @samp{PASS} command
(@pxref{password parameter}), ERC asks auth-source to match the
@var{server} parameter of @code{erc-tls} against each entry's
@samp{host} field (@w{@code{machine irc.example.net}} in the above
example).  Unfortunately, specifying a network, like
@samp{Libera.Chat}, or a specific network server, like
@samp{platinum.libera.chat}, won't normally work for looking up a
server password because that information isn't available during
opening introductions.  (Actually, ERC @emph{can} find entries with
arbitrary @samp{host} values for any context, including server
passwords, but that requires customizing the more advanced options
below.)

If ERC can't find a suitable server password, it will just skip the
IRC @samp{PASS} command altogether, something users may want when
using CertFP or engaging NickServ via ERC's @code{services} module.
If that appeals to you, consider customizing the option
@code{erc-auth-source-server-function} to @code{nil} to skip
server-password lookup for all servers.  Note that some networks and
IRCds may accept account-services authentication via server password.
Also, some ERC modules may commandeer the @code{erc-tls}
@var{password} parameter for their own ends, which likely don't
involve a server password.

@subsubheading The @samp{services} module
You can use auth-source to authenticate to account services the
traditional way through a bot called @samp{NickServ}.  To do so, add
@code{services} to @code{erc-modules} and set the option
@code{erc-use-auth-source-for-nickserv-password} to @code{t}.  After
that, expect the @samp{user} parameter in relevant auth-source queries
to be your current nickname.

Most of the time, a query's precise contextual details (such as
whether a nick was granted or forcibly assigned) shouldn't affect how
you define entries in your backend.  However, if something isn't quite
working, you may want to investigate the interplay between the option
@code{erc-nickserv-identify-mode} and account services.  In
particular, if you find yourself facing nicks suffixed with an
@code{erc-nick-uniquifier} (the infamous @samp{`}), check that the
network's entry in @code{erc-nickserv-alist} is up to date, and do let
us know if something's off (@pxref{Getting Help and Reporting Bugs}).
Of course, if you've had your fill of fiddling with this module,
consider switching to SASL for what's likely a more consistent
auth-source experience.  (@xref{SASL}.)

@subsubheading Default query behavior
When preparing entries for your backend, it may help to get a feel for
how ERC and its modules conduct searches, especially when exploring a
new context, such as channel keys.  Overall, though, ERC tries to be
consistent in performing queries across various authentication
contexts.  Here's what to expect with respect to the @samp{host}
field, which, by default, most heavily influences the fate of a query:

@enumerate
@item
entries featuring custom identifiers and networks are matched first
(@pxref{Network Identifier})
@item
followed by network-specific servers
@item
and, finally, dialed endpoints (typically the @var{server} argument
passed to @code{erc-tls})
@end enumerate

@noindent
The following netrc-style entries appear in order of precedence:

@example
machine Libera/cellphone login MyNick password sEcReT
machine Libera.Chat login MyNick password sEcReT
machine zirconium.libera.chat login MyNick password sEcReT
machine irc.libera.chat login MyNick password sEcReT
@end example

@noindent
Remember that field labels vary per backend, so @samp{machine} (in
netrc's case) maps to auth-source's generalized notion of a host,
hence the @samp{:host} keyword parameter to @code{auth-source-search}.
Also, be sure to mind the syntax of your chosen backend medium.  For
example, always quote channel names in a netrc file.

Lastly, if this all seems overly nuanced or just plain doesn't appeal
to you, please see options @code{erc-auth-source-services-function}
and friends, described just below.

@subsubheading Custom query functions
These let you query auth-source your way.  Most users can
simply ignore the passed-in arguments and get by with something like
the following:

@lisp
(defun my-fancy-auth-source-func (&rest _)
  (let* ((host (read-string "host: " nil nil "default"))
         (pass (auth-source-pick-first-password :host host)))
    (if (and pass (string-search "libera" host))
        (concat "MyNick:" pass)
      pass)))
@end lisp

@anchor{auth-source functions}
@defopt erc-auth-source-server-function
@end defopt
@defopt erc-auth-source-services-function
@end defopt
@defopt erc-auth-source-join-function

ERC calls these functions with keyword arguments recognized by
@code{auth-source-search}, namely, those deemed most relevant to the
current context, if any.  For example, when identifying to services,
@code{:user} contains your current nickname.  Generalized parameter
names, like @code{:user} and @code{:host}, are always preferred over
backend specific ones, like @code{:login} or @code{:machine}.  In
return, ERC expects a string if the search succeeds or @code{nil} if
it fails.

@findex erc-auth-source-search
The default value for all three options is the function
@code{erc-auth-source-search}.  It tries to merge relevant contextual
parameters with those provided or discovered from the logical
connection or the underlying transport.

For using auth-source along with SASL, @pxref{SASL auth-source
function}.
@end defopt

@subsubheading Channel keys
ERC also consults @code{auth-source} to find ``keys'' that may be
required by certain channels you join.  When modifying a traditional
@code{auth-source} entry for this purpose, put the channel name in the
@samp{user} field (for example, @samp{login "#fsf"}, in netrc's case).
The actual key goes in the @samp{password} (or @samp{secret}) field.

@anchor{auth-source Troubleshooting}
@subheading Troubleshooting
By default, ERC queries @code{auth-source} for channel keys and server
passwords (@pxref{auth-source Server Password}), as well as other,
module-specific credentials.  In general, if you're having trouble
calling @code{auth-source-search} in a custom query function, like
@code{erc-auth-source-server-function}, try temporarily setting the
variable @code{auth-source-debug} to @code{t} and checking
@file{*Messages*} periodically for insights into how
@code{auth-source} is operating.

If you're using a @acronym{GPG}-encrypted file and find that
customizing one of the function-valued query options doesn't solve
your problem, explore options @code{epg-pinentry-mode} and
@code{epg-debug} in the @code{epg} Custom group (@pxref{GnuPG
Pinentry,,, epa, EasyPG Assistant}).  Additionally, keep an eye out
for an @file{*Error*} buffer, which may contain more specific clues
about your situation.  If you use the libsecrets integration
(@pxref{Secret Service API,,, auth, Emacs auth-source}) with something
like GNOME Keyring, you may need to check the ``remember'' box in the
passphrase popup dialog to avoid being prompted for confirmation every
time you run ERC.  If it doesn't work at first, try logging out.  And
when in doubt, try using the Emacs command @code{secrets-show-secrets}
to browse the @samp{Login} keyring.  There should be a
@samp{GnuPG/stored-by} entry with a value of @samp{GnuPG Pinentry} or
similar.

@node display-buffer
@subsection display-buffer
@cindex display-buffer

ERC supports the ``action'' interface used by @code{display-buffer}
and friends from @file{window.el}.  @xref{Displaying Buffers,,, elisp,
Emacs Lisp}, for specifics.  When ERC displays a new or
``reassociated'' buffer, it consults its various buffer-display
options, such as @code{erc-buffer-display}, to decide whether and how
the buffer ought to appear in a window.  Exactly which one it consults
depends on the context in which the buffer is being manifested.

For some buffer-display options, the context is pretty cut and dry.
For instance, in the case of @code{erc-receive-query-display}, you're
receiving a query from someone you haven't yet chatted with in the
current session.  For other options, like
@code{erc-interactive-display}, the precise context varies.  For
example, you might be opening a query buffer with the command
@kbd{/QUERY bob @key{RET}} or joining a new channel with @kbd{/JOIN
#chan @key{RET}}.  Power users wishing to distinguish between such
nuanced contexts or just exercise more control over buffer-display
behavior generally can elect to override these options by setting one
or more to a ``@code{display-buffer}-like'' function that accepts a
@var{buffer} and an @var{action} argument.

@subsubheading Examples

In this first example, a user-provided buffer-display function
displays new server buffers in the current window when issuing an
@kbd{M-x erc-tls @key{RET}} and in a split window for all other
interactve contexts covered by the option
@code{erc-interactive-display}, like clicking an @samp{irc://}-style
@acronym{URL} (@pxref{URL}).

@lisp
(defun my-erc-interactive-display-buffer (buffer action)
  "Pop to BUFFER when running \\[erc-tls], clicking a link, etc."
  (when-let* ((alist (cdr action))
              (found (alist-get 'erc-interactive-display alist)))
    (if (eq found 'erc-tls)
        (pop-to-buffer-same-window buffer action)
      (pop-to-buffer buffer action))))

(setopt erc-interactive-display #'my-erc-interactive-display-buffer)
@end lisp

@noindent
Observe that ERC supplies the names of buffer-display options as
@var{action} alist keys and pairs them with contextual constants, like
the symbols @samp{erc-tls} or @samp{url}, the full lineup of which are
listed below.

In this second example, for Emacs 29 and above, the user writes three
predicates that somewhat resemble the ``@code{display-buffer}-like''
function above.  These too look for @var{action} alist keys sharing
the names of ERC's buffer-display options (and, in one case, a
module's minor mode).

@lisp
(defun my-erc-disp-entry-p (_ action)
  (memq (cdr (or (assq 'erc-buffer-display action)
                 (assq 'erc-interactive-display action)))
        '(erc-tls url)))

(defun my-erc-disp-query-p (_ action)
  (or (eq (cdr (assq 'erc-interactive-display action)) '/QUERY)
      (and (eq (cdr (assq 'erc-receive-query-display action)) 'PRIVMSG)
           (member (erc-default-target) '("bob" "alice")))))

(defun my-erc-disp-chan-p (_ action)
  (or (assq 'erc-autojoin-mode action)
      (and (eq (cdr (assq 'erc-buffer-display action)) 'JOIN)
           (member (erc-default-target) '("#emacs" "#fsf")))))
@end lisp

@noindent
You'll notice we ignore the @var{buffer} parameter of these predicates
because ERC ensures that @var{buffer} is already current (which is why
we can freely call @code{erc-default-target}).  Note also that we
cheat a little by treating the @var{action} parameter like an alist
when it's really a cons of one or more functions and an alist.

@noindent
To complement our predicates, we set all three buffer-display options
referenced in their @var{action}-alist lookups to
@code{display-buffer}.  This tells ERC to defer to that function in
the display contexts covered by these options.

@lisp
(setopt erc-buffer-display #'display-buffer
        erc-interactive-display #'display-buffer
        erc-receive-query-display #'display-buffer
        ;;
        erc-auto-reconnect-display 'bury)
@end lisp

@noindent
The last option above just tells ERC to avoid any buffer-display
machinery when auto-reconnecting.  (For historical reasons, ERC's
buffer-display options use the term ``bury'' to mean ``ignore'' rather
than @code{bury-buffer}.)

Finally, we compose our predicates into @code{buffer-match-p}
conditions and pair them with various well known @code{display-buffer}
action functions and action-alist members.

@lisp
(setopt display-buffer-alist

        ;; Create new frame with M-x erc-tls RET or (erc-tls ...)
        '(((and (major-mode . erc-mode) my-erc-disp-entry-p)
           display-buffer-pop-up-frame
           (reusable-frames . visible))

          ;; Show important chans and queries in a split.
          ((and (major-mode . erc-mode)
                (or my-erc-disp-chan-p my-erc-disp-query-p))
           display-buffer-pop-up-window)

          ;; Ignore everything else.
          ((major-mode . erc-mode)
           display-buffer-no-window
           (allow-no-window . t))))
@end lisp

@noindent
Of course, we could just as well set our buffer-display options to one
or more homespun functions instead of bothering with
@code{display-buffer-alist} at all (in what would make for a more
complicated version of our first example).  But perhaps we already
have a growing menagerie of similar predicates and like to keep
everything in one place in our @file{init.el}.

@subsubheading Action alist items

@table @asis
@item Option-based keys:
All keys are symbols, as are values, unless otherwise noted.

@itemize @bullet
@item @code{erc-buffer-display}
@itemize @minus
@item @samp{JOIN}
@item @samp{NOTICE}
@item @samp{PRIVMSG}
@item @samp{erc} (entry point called non-interactively)
@item @samp{erc-tls}
@end itemize

@item @code{erc-interactive-display}
@itemize @minus
@item @samp{/QUERY}
@item @samp{/JOIN}
@item @samp{/RECONNECT}
@item @samp{url} (hyperlink clicked)
@item @samp{erc} (entry point called interactively)
@item @samp{erc-tls}
@end itemize

@item @code{erc-receive-query-display}
@itemize @minus
@item @samp{NOTICE}
@item @samp{PRIVMSG}
@end itemize

@item @code{erc-auto-reconnect-display}
@itemize @minus
@item something non-@code{nil}
@end itemize
@end itemize

@item Module-based (minor-mode) keys:

@itemize @bullet
@item @code{erc-autojoin-mode}
@itemize @minus
@item channel name as a string, e.g., @code{"#chan"}
@end itemize
@end itemize
@end table

@node Module Loading
@section Module Loading
@cindex module loading

ERC loads internal modules in alphabetical order and third-party
modules as they appear in @code{erc-modules}.  When defining your own
module, take care to ensure ERC can find it.  An easy way to do that
is by mimicking the example in the doc string for
@code{define-erc-module} (also shown below).  For historical reasons,
ERC falls back to @code{require}ing features.  For example, if some
module @code{my-module} in @code{erc-modules} lacks a corresponding
@code{erc-my-module-mode} command, ERC will attempt to load the
library @code{erc-my-module} prior to connecting.  If this fails, ERC
signals an error.  Users defining personal modules in an init file
should @code{(provide 'erc-my-module)} somewhere to placate ERC.
Dynamically generating modules on the fly is not supported.

Some older built-in modules have a second name along with a second
minor-mode toggle, which is just a function alias for its primary
counterpart.  For practical reasons, ERC does not define a
corresponding variable alias because contending with indirect
variables complicates bookkeeping tasks, such as persisting module
state across IRC sessions.  New modules should definitely avoid
defining aliases without a good reason.

Some packages have been known to autoload a module's definition
instead of its minor-mode command, which severs the link between the
library and the module.  This means that enabling the mode by invoking
its command toggle isn't enough to load its defining library.  As
such, packages should only supply module-related autoload cookies with
an actual @code{autoload} form for their module's minor-mode command,
like so:

@lisp
;;;###autoload(autoload 'erc-my-module-mode "erc-my-module" nil t)
(define-erc-module my-module nil
  "My doc string."
  ((add-hook 'erc-insert-post-hook #'erc-my-module-on-insert-post))
  ((remove-hook 'erc-insert-post-hook #'erc-my-module-on-insert-post)))
@end lisp

@noindent
As implied earlier, packages can usually omit such cookies entirely so
long as their module's prefixed name matches that of its defining
library and the library's provided feature.

Finally, packages have also been observed to run
@code{erc-update-modules} in top-level forms, forcing ERC to take
special precautions to avoid recursive invocations.  Another
unfortunate practice is mutating @code{erc-modules} itself upon
loading @code{erc}, possibly by way of an autoload.  Doing this tricks
Customize into displaying the widget for @code{erc-modules}
incorrectly, with built-in modules moved from the predefined checklist
to the user-provided free-form area.

@node Match API
@section Match API
@cindex low-level match

This section describes the low-level @samp{match} @acronym{API}
introduced in ERC 5.7.  For basic, options-oriented usage, please see
the doc strings for option @code{erc-pal-highlight-type} and friends in
the @code{erc-match} group.  Unfortunately, those options often prove
insufficient for more granular filtering and highlighting needs, and
advanced users eventually outgrow them.  However, under the hood, those
options all use the same foundational @code{erc-match} API, which
centers around a @code{cl-defstruct} @dfn{type} of the same name:

@deftp {Struct} erc-match @
  predicate spkr-beg spkr-end body-beg sender nick command handler

  This is a @code{cl-struct} type that contains some handy facts about
  the message being processed.  That message's formatted body occupies
  the narrowed buffer when ERC creates and provides access to each
  @code{erc-match} instance.  To use this interface, you add a
  @dfn{constructor}-like function to the hook
  @code{erc-match-functions}:

  @defopt erc-match-functions

  An abnormal hook for which each member accepts the parameters named
  above as an @samp{&rest}-style plist and returns a new
  @code{erc-match} instance.  A function can also be a traditional
  @code{cl-defstruct}-provided constructor belonging to a @dfn{subtype}
  you've defined.

  @end defopt

  The only slot you definitely need to specify is @samp{predicate}.
  Both it and @samp{handler} are functions that take a single argument:
  the instance itself.  As its name implies, @samp{predicate} must
  return non-@code{nil} if @samp{handler}, whose return value ERC
  ignores, should run.

  A few slots, like @samp{spkr-beg}, @samp{spkr-end}, and @samp{nick},
  may surprise you.  The first two are @code{nil} for non-chat messages,
  like those displayed for @samp{JOIN} events.  The @samp{nick} slot can
  likewise be @code{nil} if the sender of the message is a domain-style
  host name, such as @samp{irc.example.org}, which it often is for
  informational messages, like @samp{*** #chan was created on 2023-12-26
  00:36:42}.

  To locate the start of the just-inserted message, use @samp{body-beg},
  a marker indicating the beginning of the message proper.  Don't
  forget: all inserted messages include a trailing newline.  If you want
  to extract just the message body's text, use the function
  @code{erc-match-get-message-body}:

  @defun erc-match-get-message-body match

  Takes an @code{erc-match} instance and returns a string containing the
  message body, sans trailing newline and any leading speaker or
  decorative component, such as @code{erc-notice-prefix}.

  @end defun

@end deftp

@noindent
Although module authors may want to subclass this struct, everyday users
can just instantiate it directly (it's @dfn{concrete}).  This is
especially handy for one-off tasks or simple customizations in your
@file{init.el}.  To do this, define a function that invokes its
constructor:

@lisp
(require 'erc-match)

(defvar my-mentions 0)

(defun my-match (&rest plist)
  (apply #'erc-match
         :predicate (lambda (_) (search-forward "my-project" nil t))
         :handler (lambda (_) (cl-incf my-mentions))
         plist))

(add-hook 'erc-match-functions #'my-match)
(setopt erc-prompt (lambda () (format "%d!" my-mentions)))
@end lisp

@noindent
Here, the user could just as well shove the incrementer into the
@samp{predicate} body, since @samp{handler} is set to @code{ignore} by
default (however, some frown at the notion of a predicate exhibiting
side effects).  Likewise, the user could also choose to concentrate only
on chat content by filtering out non-@samp{PRIVMSG} messages via the
slot @samp{command}.

For a detailed example of matching without highlighting, see the
@samp{jabbycat} demo module, available on ERC's dev-oriented package
archive: @uref{https://emacs-erc.gitlab.io/bugs/archive/jabbycat.html}.
If you're in a hurry, check out @file{erc-desktop-notifications.el},
which ships with ERC, but please ignore the parts that involve adapting
the global setup (and teardown) business to a buffer-local context.
Since your module is declared @code{local}, as per the modern
convention, you won't be needing such code, so feel free to do things
like add local members to @code{erc-match-functions} in your module's
definition.

@anchor{highlighting}
@subsection Highlighting
@cindex highlighting

Third-party modules likely want to manage and apply faces themselves.
However, in a pinch you can just piggyback atop the highlighting
functionality already provided by @samp{match} to support its many
high-level options.

@lisp
(require 'erc-match)

(defvar my-keywords
  `((foonet ("#chan" ,(rx bow (or "foo" "bar" "baz") eow)))))

(defface my-face
  '((t (:inherit font-lock-constant-face :weight bold)))
  "My face.")

(defun my-match (&rest plist)
  (apply #'erc-match-opt-keyword
         :data (and-let* ((chans (alist-get (erc-network) my-keywords))
                          ((cdr (assoc (erc-target) chans)))))
         :face 'my-face
         plist))

(add-hook 'erc-match-functions #'my-match)
@end lisp

@noindent
Here, the user leverages a handy subtype of @code{erc-match}, called
@code{erc-match-opt-keyword}, which actually descends directly from
another, intermediate @code{erc-match} type:

@deftp {Struct} erc-match-traditional category face data part

Use this type or one of its descendants (see below) if you want
@code{erc-text-matched-hook} to run alongside (after) the @samp{handler}
slot's default highlighter, @code{erc-match-highlight}, on every match
for which the @samp{category} slot's value is non-@code{nil} (it becomes
the argument provided for the hook's @var{match-type} parameter).

Much more important, however, is @samp{part}.  This slot determines what
portion of the message is being highlighted or otherwise operated on.
It can be any symbol, but the ones with predefined methods are
@code{nick}, @code{message}, @code{all}, @code{keyword},
@code{nick-or-keyword}, and @code{nick-or-mention}.

The complement to the @samp{part} slot is @samp{data}, which holds the
value of the module's option corresponding to the specific type.  For
example, ERC initializes the @samp{data} slot for the
@code{erc-match-opt-pal} type with the value of @code{erc-pals}.

The default handler, @code{erc-match-highlight}, does its work by
deferring to a purpose-built @dfn{method} meant to handle
@samp{part}-based highlighting:

@defop {Method} erc-match-traditional erc-match-highlight-by-part @
  instance part

  You can override this method by @dfn{specializing} on any subclassed
  @code{erc-match-traditional} type and/or non-reserved @var{part}, such
  as one known only to your @file{init.el} or (informally) associated
  with your package by its library @dfn{namespace}.

@end defop

@end deftp

@noindent
You likely won't be needing these, but for the sake of completeness,
other options-based types similar to @code{erc-match-opt-keyword}
include @code{erc-match-opt-current-nick}, @code{erc-match-opt-fool},
@code{erc-match-opt-pal}, and @code{erc-match-opt-dangerous-host}.  (If
you're familiar with this module's user options, you'll notice some
parallels here.)

And, finally, here's a more elaborate, module-like example demoing
highlighting based on the @code{erc-match-traditional} type:

@lisp
;; -*- lexical-binding: t; -*-

(require 'erc-match)
(require 'erc-button)

(defvar my-keywords
  `((foonet ("#chan" ,(rx bow (or "foo" "bar" "baz") eow)))))

(defface my-keyword '((t (:underline (:color "tomato" :style wave))))
  "My face.")

(defun my-get-keyword ()
  (and-let* ((chans (alist-get (erc-network) my-keywords))
             ((cdr (assoc (erc-target) chans))))))

(cl-defstruct (my-match (:include erc-match-opt-keyword
                                  (data (my-get-keyword))
                                  (face 'my-keyword))
                        (:constructor my-match)))

(add-hook 'erc-match-functions #'my-match)

(cl-defmethod erc-match-highlight-by-part ((instance my-match)
                                           (_ (eql keyword)))
  "Highlight keywords by merging instead of clobbering."
  (dolist (pat (my-match-data instance))
    (goto-char (my-match-body-beg instance))
    (while (re-search-forward pat nil t)
      (erc-button-add-face (match-beginning 0) (match-end 0)
                           (my-match-face instance)))))
@end lisp

@noindent
Note that in the method body, you @emph{could} technically skip to the
beginning of the last match for the first go around because the match
data from the @samp{predicate} is still fresh.  Also, while the method
could simply call @code{my-get-keyword} directly instead of accessing
the @samp{data} slot and also reference the @code{my-keyword} face
instead of using the @samp{face} slot, other methods may need to share
@samp{data} or alter @samp{face}.


@node Options
@section Options
@cindex options

@c PRE5_4: (Node) Document every ERC option (module options go in
@c previous chapter)

This section is extremely incomplete.  For now, the easiest way to
check out all the available options for ERC is to do
@kbd{M-x customize-group @key{RET} erc @key{RET}}.

@defopt erc-hide-list
If non, @code{nil}, this is a list of IRC message types to hide, e.g.:

@example
(setq erc-hide-list '("JOIN" "PART" "QUIT"))
@end example
@end defopt

@defopt erc-network-hide-list
If non, @code{nil}, this is a list of IRC networks and message types
to hide, e.g.:

@example
(setq erc-network-hide-list (("Libera.Chat" "JOIN" "PART" "QUIT")
("OFTC" "JOIN" "PART""))
@end example
@end defopt

@defopt erc-channel-hide-list
If non, @code{nil}, this is a list of IRC channels and message types
to hide, e.g.:

@example
(setq erc-channel-hide-list (("#erc" "JOIN" "PART" "QUIT")
("#emacs" "NICK"))
@end example
@end defopt

@defopt erc-lurker-hide-list
Like @code{erc-hide-list}, but only applies to messages sent by
lurkers.  The function @code{erc-lurker-p} determines whether a given
nickname is considered a lurker.
@end defopt

@node Getting Help and Reporting Bugs
@chapter Getting Help and Reporting Bugs
@cindex help, getting
@cindex bugs, reporting

After you have read this guide, if you still have questions about ERC,
or if you have bugs to report, there are several places you can go.

@itemize @bullet

@item
@uref{https://www.emacswiki.org/emacs/ERC} is the
emacswiki.org page for ERC@.  Anyone may add tips, hints, etc.@: to it.
If you do so, please help keep it up to date.

@item
You can ask questions about using ERC on the Emacs mailing list,
@uref{https://lists.gnu.org/mailman/listinfo/help-gnu-emacs}, as well
as on ERC's own low-volume list,
@uref{https://lists.gnu.org/mailman/listinfo/emacs-erc}.

@item
You can visit the IRC Libera.Chat channel @samp{#emacs}.  Many of the
contributors are frequently around and willing to answer your
questions.  You can also try the relatively quiet @samp{#erc}, on the
same network, for more involved questions.

@item
@anchor{Upgrading}
You can check GNU ELPA between Emacs releases to see if a newer
version is available that might contain a fix for your issue:
@uref{https://elpa.gnu.org/packages/erc.html}.

To upgrade, run @kbd{M-x list-packages @key{RET}}.  In the
@file{*Packages*} (@code{package-menu-mode}) buffer, click the
@samp{erc} package link for the desired version.  If unsure, or if the
version column is too narrow to tell, try the bottom-most candidate.
In the resulting @code{help-mode} buffer, confirm the version and
click @samp{Install}.  Make sure to restart Emacs before reconnecting
to IRC, and don't forget that you can roll back to the previous
version by running @kbd{M-x package-delete @key{RET}}.
@xref{Packages,,,emacs, The Emacs Editor}, for more information.

Note that a bug affecting Emacs's packaging machinery may prevent the
above method from working on Emacs versions 29 and below.  Users on 29
can try running @kbd{C-u M-x package-install @key{RET}} instead.
Users on 28 and below can click on the @emph{installed} @samp{erc}
line item in the @file{*Packages*} buffer instead of the newest one,
and then, in the resulting @code{help-mode} buffer, find and activate
the button for the newest version, which should appear in the summary
item @samp{Other versions}.

In the rare instance you need an emergency fix or have volunteered to
test an edge feature between ERC releases, you can try adding
@samp{("devel" . "https://elpa.gnu.org/devel/")} to
@code{package-archives} prior to performing the steps above.  For
this, you'll want to instead select a @dfn{snapshot} version from the
menu.  Please be aware that when going this route, the latest changes
may not yet be available and you run the risk of incurring other bugs
and encountering unstable features.

@item
To report a bug in ERC, use @kbd{M-x erc-bug}.

@end itemize


@node History
@chapter History
@cindex history, of ERC

@c abel@@bfr.co.il, sergey.berezin@@cs.cmu.edu
ERC was originally written by Alexander L. Belikoff and Sergey Berezin.
They stopped development around
December 1999.  Their last released version was ERC 2.0.

P.S.: If one of the original developers of ERC reads this, we'd like to
receive additional information for this file and hear comments in
general.

@itemize
@item 2001

@c mlang@@delysid.org, alex@@gnu.org
In June 2001, Mario Lang and Alex Schroeder
took over development and created a ERC Project at
@uref{https://sourceforge.net/projects/erc}.

In reaction to a mail about the new ERC development effort, Sergey
Berezin said, ``First of all, I'm glad that my version of ERC is being
used out there.  The thing is, I do not have free time and enough
incentive anymore to work on ERC, so I would be happy if you guys take
over the project entirely.''

So we happily hacked away on ERC, and soon after (September 2001)
released the next "stable" version, 2.1.

Most of the development of the new ERC happened on @samp{#emacs} on
irc.openprojects.net.  Over time, many people contributed code, ideas,
bugfixes, and a lot of alpha/beta/gamma testing.

See the @file{CREDITS} file for a list of contributors.

@item 2003

ERC 3.0 was released.

@item 2004

ERC 4.0 was released.

@item 2005

@c mwolson@@gnu.org
ERC 5.0 was released.  Michael Olson became
the release manager and eventually the maintainer.

After some discussion between him and the Emacs developers, it was
decided to include ERC in Emacs.

@item 2006

ERC 5.1 was released.  It was subsequently included in Emacs 22.

ERC became an official GNU project, and development moved to
@uref{https://sv.gnu.org/projects/erc}.  We switched to using GNU Arch as
our revision control system.  Our mailing list address changed as well.

@item 2007

We switched to using git for our version control system.

@item 2009+

Since about 2009, ERC is no longer developed as a separate project, but
is maintained as part of Emacs.

@end itemize

@anchor{Official IRC channels}
@subheading Official IRC channels
@cindex official IRC channels

The official channels for GNU Emacs and ERC lived on the Freenode IRC
network until June 2021, when they---along with the official IRC
channels of the GNU Project, the Free Software Foundation, and many
other free software communities---relocated to the Libera.Chat network
in the aftermath of changes in governance and policies of Freenode in
May and June 2021.  GNU and FSF's announcements about this are at
@uref{https://lists.gnu.org/archive/html/info-gnu/2021-06/msg00005.html},
@uref{https://lists.gnu.org/archive/html/info-gnu/2021-06/msg00007.html},
and
@uref{https://lists.gnu.org/archive/html/info-gnu-emacs/2021-06/msg00000.html}.

@node GNU Free Documentation License
@appendix GNU Free Documentation License
@include doclicense.texi

@node Concept Index
@unnumbered Index

@printindex cp

@bye