In Chapter 9, Aliases an alias that
replaces dt with drink from
fountain was described. To create this alias, enter the
following parameters, leaving the other options unchanged from the
default values:
Pattern: ^df$
Substitution: drink from fountain
You might be wondering why we use "^df$" and
not only "df". Remember that aliases are just
substitutions, and the pattern is a regular expression. If the anchors
(that is, ^ and $) were not
present, it would match against df anywhere in
the line, and substitute this df even in the
middle of words. wonder would become
wodrink from fountainder. At times a behaviour
like this (substituting anywhere) might be desirable, but in our case
we want it to substitute only the whole command
df, so we use the anchors.
As an example of an alias that does not match only the exact command, consider this one:
Pattern: '^gra ' (without the
quotes, but note the space after the word)
Substitution: 'chat CONGRATULATIONS,
' (without the quotes, but note the space after the
word)
Whenever you enter a command that starts with
gra followed by a space, that part
(gra and the space) is replaced by the given
pattern. So if you enter gra Bob, what will be
sent to the MUD is chat CONGRATULATIONS,
Bob.
Since aliases are just a substitution, you can define bracketed
expressions in the pattern and then use $1,
$2, and so on in the substitution. Let us increment
the above example to add something to the end. We will need a
bracketed expression:
Pattern: ^gra (.*)$
Substitution: chat CONGRATULATIONS, $1!!!
It should be easy to understand. $1 in the
substituion is replaced by what goes after
gra.
As mentioned in Section 9.1.1, “Adding Aliases”, aliases
can use a s//e construct, that is, whose
substitution is actually composed of Perl statements evaluated when a
match is found.
To use that feature, select the Eval substitution as Perl statement option:
Pattern: calc\((.*)\)
Substitution: eval "$1"
Eval substitution as Perl statement: checked
The alias allows you to write something like that:
gossip 2+3 = calc(2+3) and have the result of
the calculation sent to the MUD. (Or any other Perl statement to be
evaluated, actually.)
By default, case is considered when matching. If you want case-insensitive matching, select Ignore case when matching.
It is possible to make an alias whose action is not to send a changed command line, but to execute an action.
To do that, make the replacement start with
/, which means that the rest of the line will be
executed, and not sent to the mud. In the rest of the line, you can
put arbitrary Perl code. However, if you want to refer to a variable,
you must escape the $ prefix by writing it as
\$. This way, when the substitution is run, you get
the name of the variable, not the value this variable currently
has.
As an example, if you define an alias with pattern
^say (.*)$ and action
/\$world-\>echonl("$1"), whenever you type a
line that starts with say in the input box, the
rest of the line will be echoed in the screen, but not sent to the
mud.