=head1 NAME

Cisco::Reconfig - Parse and generate Cisco configuration files

=head1 SYNOPSIS

	use Cisco::Reconfig;

	my $config = readconfig("/my/cisco/config");
	my $config = stringconfig("cisco config", "goes here");

=head1 DESCRIPTION

Cisco::Reconfig makes it easier to write programs to generate changes to Cisco
configuration files.

Cisco::Reconfig is a module that parses Cisco router configuration files.  It
doesn't have any real understanding of Cisco configurations so it
might be useful for other similar configuration languages.  It knows
that nesting is shown by indentation.  It knows that C<!> means a
comment.  It knows that C<no> may proceed a line without changing
where that line exists in the hierarchy.  It doesn't know much else.

Cisco::Reconfig can be used to modify configurations.  The C<set()> method 
will check the current configruation and return commands to change
it if it is other than what is wanted (as passed to the C<set()>
method).

=head2 DETAILS

Some of the accessor methods return a special "undef" object instead
of a proper undef.  This is so that code that uses accessors 
doesn't have to be paranoid about undefined values.  This "undef" object
tests as false in boolean context however it is C<defined()>ed.

Methods that return configuration items can return items that
represent any particular word in the configruation file.  For
example, with the following configuration & code, the return
value for the C<get()> method would represent the word
C<access-list> in both of the lines:

	ip as-path access-list 111 deny _10993_
	ip as-path access-list 111 permit .*

	$config->get('ip as-path access-list');

Most of the time you don't need to worry about the fact that the
object represents a word.  Another way to look at it is that the
object represents a selection of lines from the configuration file.
Sometimes that selection is a single line.  Sometimes it is a block.
Sometimes it is a few lines that start with the same tokens.

To look at all the different as-path access
lists, the following would work:

	$config->get('ip as-path access-list')->all;

The word C<no> is handled specially: it is discarded.  Many cisco
directives start with the word C<no>.  To make the module more
usable, the word C<no> is ignored during parsing.  It is kept in
the text so, if you look for something that might have a C<no> 
in front of it, you'll get a hit if the C<no> is there or isn't
there.  For example:

	my (@cdp_disabled);
	for my $context ($config->get('interface')->all(qr{^ether}i)) {
		my $cdp = $context->get('cdp enable');
		push(@cdp_disabled, $context)
			if $cdp =~ /no cdp enable/;
	}

=head1 FUNCTIONS

There is just one function provided: C<readconfig()>.  Readconfig
takes a single argument: a filename or file handle.  It parses
the file and returns an Cisco::Reconfig object.

=head1 MAIN METHODS

=over 4

=item ->get(@designators)

The C<get()> method is the key to looking up items in a configuration
file.  It takes an array of designators as an argument.  A designator
is simply something that identifies a portion of a configuration
file.  For example C<('interface')> is a designator for all the interfaces
and C<('ip route')> is a designator for all the static routes.

When multiple designators are specified, they are used for nested
configuration items.  For example, 
C<('router bgp', 'neighbor')> would be a designator for all the
BGP neighbors.  This assumes that there is only one C<router bgp>
defined.

In array context, C<get()> will follow multiple paths to find 
configuration items that match the specification.  For example
C<('interface', 'ip address')> would return a list of ip address
items across multiple interfaces.

Designators must exactly match words in the configuration.  You may
not abbr anythng.

=item ->set(@designators, $newvalue)

The C<set()> method will generate Cisco configuration snippets
that will modify the configuration of an item.  For example,
the following code:

	my $ser0 = $config->get('interface Serial0');
	print $ser0->set('ip address', 
		'ip address 207.181.198.194 255.255.255.252');

Will print:

	interface Serial0
	 ip address 207.181.198.194 255.255.255.252
	exit

If the configuration already matches the C<$newvalue> then
nothing would be printed.

The designator(s) say what will be modified.  This should either
be represent a line or an entire block.  When multiple designators
are needed, pass them as an anonymous array.  The above example
could also have been written as:

	print $config->set('interface Serial0', 'ip address',
		'ip address 207.181.198.194 255.255.255.252');

If no designators are needed, don't pass any.  The following
is nearly the same as the preceeding;

	my $ipaddr = $config->get('interface Serial0', 'ip address');
	print $ipaddr->set( 'ip address 207.181.198.194 255.255.255.252');

When providing code snippets to C<set()>, indent blocks just like
Ciscos do when they display their configuration.  For example, the
following:

	print $config->set("ip access-list extended all-addresses", <<END);
		ip access-list extended all-addresses
		 permit ip any any
		!
	END

Will print the following if the access list ins't already set as
listed:

	ip access-list extended all-addresses
	 permit ip any any
	exit

When modifying a block, include the configruation line that starts
the block in the replacement text.  For example, when setting an entire
interface, provide the entire block:

	print $config->set('interface Serial0',<<END);
		interface Serial0 point-to-point
		 ip address 219.22.221.3 255.255.255.252
		 bandwidth 3022
		!
	END

=item ->all($regex)

The C<all()> method can be used to expand and select configuration
items.

For example, to make sure that all loopback interfaces use a 
netmask of 255.255.255.255, use the following:

	for my $loop ($config->get('interface')->all(qr{^Loop})) {
		my $ip = $loop->get('ip address');
		next unless $ip->text =~ /\A\s*ip address (\S+) \S+\s*\Z/;
		print $ip->set(undef, "ip address $1 255.255.255.255");
	}

The C<$regex> paramater is optional. 

=back

=head1 ACCESSOR METHODS

=over 4

=item ->single()

Cisco::Reconfig objects may represent any word in a configruation file.
For example the word "address" in the following is represented by
an object that would be returned by the code that follows.

	interface Loopback0 
	 ip access-group 151 in
	 ip address 218.28.41.38 255.255.255.255
	!

	my $address_word = $config->get('interface Loopback0', 'ip')
		->all(qr{^address});

C<single()> answers the question: does this Cisco::Reconfig object
uniquely specify a single point in the configuration?  In the example
above, the object for word C<ip> (above) does not but the object
for the word C<address> does.

C<single()> returns an object (representing the last word on the
line) or undef.

=item ->zoom()

C<zoom()> is the same as to C<single()> except that it will always
return a valid Cisco::Reconfig object.  

=item ->endpt()

Returns an Cisco::Reconfig object representing the last word on a configuration
line that could follow from the current ZYZ object.  When there are
multiple possibilities the object picked is nearly random.

=item ->next()

C<next()> returns an Cisco::Reconfig object representing the last word on the
suceeding line of the current configuration block.

When used at the beginning of a block, it returns the last word of
the first line in the block.

=item ->context()

Returns the configuration object that represents the surounding context.

	# returns the "undefined" object
	$config->context 

	# returns $config
	$config->get('interface Loopback0')->context 

	# returns $config->get('interface Loopback0')
	$config->get('interface Loopback0', 'ip address')->context 

C<context()> always returns a configuration object.

=item ->subs()

For Cisco::Reconfig objects that represent a word in a line that introduces
a block of configuration items (such as most C<interface> lines),
the C<subs()> function returns an Cisco::Reconfig object that represents the
contents of the block.

If the Cisco::Reconfig object in question does not represent the start of a
configuration block, the "undefined" object is returned.

=item ->kids()

For Cisco::Reconfig objects that do not uniquely specify a single line
(ie: C<! ->single()>), the ->kids() method will return an array
of objects representing the possible following words.  

If there is only one possibility, that one possibility is returned.

If the Cisco::Reconfig object represents the last word on a configuration line
then that word is returned.

=back

=head1 MISCELLANEOUS METHODS

=over 4

=item ->text()

Returns the text from the original configuration file (in original
order) of all of the lines that could follow from the current Cisco::Reconfig
object.  

When the invoking Cisco::Reconfig object represents a single line C<text()>
returns that line.  When the invoking Cisco::Reconfig object represents a 
block C<text()> returns the entire block.  When the Cisco::Reconfig object
represents a word with multiple possible completions, C<text()>
returns all the completions.

=item ->alltext()

Returns the text from the original configuration file of all the lines that could
follow from the current Cisco::Reconfig object and all lines that are introduced
by the current object. 

To get the text of all interface definitions in their entirety, use;
	
	$config->get('interface')->alltext

=item ->setcontext()

Returns an array of configuration lines that define the block
surrounding the invoking object.

=item ->unsetcontext()

Returns an array of the word C<exit> repeated as many times as
nessasary to undo a C<setcontext()>.

=item ->block()

Returns true if the object represents a whole configuration block.

=back

=head1 TWEAKS

Some cisco configurations have a minus one indent beginning with the
C<class> keyword.  This exception is matched and handled.  To change the
regex for what is accepted for a minus-one indent, override
C<$Cisco::Reconfig::allow_minus_one_indent> to a new regex.

=head1 OVERLOADING

Two operators are overloaded: boolean tests and stringification.
Cisco::Reconfig objects booleanify as true if they are the special undefined
objects.  Cisco::Reconfig objects stringify as their text lines.

=head1 CAVEATS

Since Cisco::Reconfig doesn't really understand Cisco configuration files
it can't know things that you might think it should.

For example, it doesn't know that C<interface Serial0> is the
same as C<int ser 0> nor even C<interface Serial 0>.  Be very
careful about where Cisco's actually put spaces and where they 
don't.

No attempt has been made to make this module particularly fast
or efficient for the computer.

Cisco::Reconfig objects don't automatically garbage collect themselves because
they are highly self-referrential.

=head1 LICENSE

Copyright (C) 2002-2010 David Muir Sharnoff <cpan@dave.sharnoff.org>
Copyright (C) 2011-2012 Google, Inc.
This module may be licensed on the same terms as Perl itself.

