For those more used to Perl and to command lines, it is also possible to define and alter aliases from the command line. This is done with a series of Perl function.
Aliases are defined with the
$world->alias function. This function works
similarly to $world->trigger (described in
Chapter 8, Triggers).
The simplest way to call the function is with two arguments:
$world->alias(. This defines an
alias with the given pattern,
substitution)pattern and
substitution. For example, the alias
described in Example 9.1, “A simple alias” would be created as
follows:
$world->alias('^df$', 'drink from fountain')
Like the $world->trigger function (see
Section 8.6, “Defining Triggers in the Command Line”), you can specify extra
arguments to control advanced alias features. One such argument
is perleval that causes the substitution to be
evaluated as a Perl statement. The alias defined in
Example 9.4, “An alias whose substitution is evaluated:” can also be created as
follows:
$world->alias('calc\((.*)\)', 'eval "$1"',
{ perleval => 1})
See the difference? There is a third parameter, enclosed in
curly braces {}, with the word
perleval, an arrow, and the number 1. What that
means is that perleval has the value 1, or, as
usual in computer languages, is true. (False would be zero.)
To specify a case-insensitive match, use the
ignorecase attribute.
Before going into editing, let us see how to get a list of all
aliases that are currently defined for the World. Just use the
$world->listalias function without arguments. You
will be presented with a list of the currently defined aliases.
There are four columns: Num is
the number of the alias. Aliases are numbered sequentially starting at
zero. This number will be useful when we start editing aliases. After
that, Ena tells whether the alias is
enabled. Aliases that are disabled are not tried. This is a nice way
to stop an alias from working, but keep it stored for later use. We
will see how to enable and disable aliases later in this section. The
final two columns list the pattern and substitution of the
alias.
The listing produced by $world->listalias
is compact, showing all aliases but possibly truncating the pattern
and/or substitution. If you give an alias number as argument to
listalias, it will display that alias's
information detailedly.
To edit an alias, you need to know that alias's number. (And
that can be discovered with the listing functions just described.
Alternatively, the $world->getaliasnumber can be
used to discover an alias's number if its name is known.) The same
function used to add aliases can also change existing ones, you just
need to pass the alias number as the first argument.
Calling
$world->alias( changes the pattern
of the alias with that number. If you want to change the pattern and
substitution, include the substitution as a third argument:
number,
new pattern)$world->alias(. What if you want to change
only the substitution? Since passing only one string argument would
change the pattern, this is done in a different way. In brief, this is
how you would change only the substitution:
number,
new pattern, new
substitution)$world->alias(. Notice that the substitution is passed as an attribute
inside the curly braces. It is also possible to change the pattern
this way, just use the attribute number, {
substitution => new substitution
})pattern.
One other attribute of aliases is enabled. It
was mentioned briefly when we described how to list aliases. It can be
set just like the other attributes and is binary,
that is, takes the values true (represented by
anything different from 0) or false (represented
by 0). When the value of this attribute is true (which is the
default), the alias is tried normally. When it is zero, commands are
not tried against it. This way, disabling an alias effectively turns
if off, as if it did not exist, but the alias is still saved, and can
be turned on again when necessary.
Here's an example of disabling an alias (number 3 in this case):
$world->alias(3,
{ enabled => 0 })
However, there is a shorter way: the
$world->disalias function disables the alias
whose number is passed as argument. So the example above can be
rewritten in a shorter way as:
$world->disalias(3)
The corresponding function $world->enaalias
enables the specified alias.
It is also possible to temporarily disable all aliases. Just use the menu → and this will prevent aliases from being used. This does not change the "enabled" status of any aliases, it just prevents all aliases from being executed. When you select the menu again, aliases that were enabled will be matched again, and those that were disabled will remain disabled.
There are times when you want to delete an alias. This is easy
to do, use the $world->delalias function. It
takes as argument the number of the alias you wish to delete. Be aware
that once deleted it is not possible to recover the alias (unless you
create it again). Many times just disabling the alias is a better
idea. The second thing to note is that when you delete an alias the
numbers of the other aliases may change, so be careful when you try to
delete several aliases in sequence.
It is possible to assign names to aliases. When an alias has a name, you can enable, disable, or delete it using its name instead of its number.
To assign a name to an alias, specify the
name attribute when creating it:
$world->alias('^df$', 'drink from fountain',
{ name => 'drink' })
You can now disable this alias with
$world->disalias('drink'). The name can also
be used in the $world->enaalias,
$world->delalias and
$world->listalias functions.
It is also possible to assign a name to an existing alias.
Just edit it as described in Section 9.3.1, “Editing Aliases”,
passing the name attribute. Use this same process
to change the name of an alias.
Another feature of alias names is that several aliases can have the same name. In this case, all these aliases will be treated as a single group. The functions above, when passed an alias name, will act upon all aliases of the group, that is, on all aliases with that name.
Aliases are tried from the first to the last, so in some cases
the order of the aliases matters. It is possible to move an alias to
another position with the $world->movealias
function.
The function takes two parameters: the first is the name or number of the alias that you want to move. The second is the new position that the alias will take in the list. 0 means move the the first position. If you specify a negative number or a number greater than the number of aliases, the alias will be moved to the end of the list.
If there are several aliases with the same name, only the first one found will be moved. And when an alias is moved, other aliases might move up or down to accomodate the change.