When looking up information or performing actions with the
$( and $) operators, it is
sometimes necessary to provide positional substitution arguments. To
illustrate, consider an entry such as this in a hypothetical database
With such an entry in place, and having built the database, the
following rule could be used to perform a lookup:
R$- @ $-.uucp $: $(uucp $2 $@ $1 $@ mailhost $: $1.$2.uucp $)
Here, if the workspace contains the address
joe@hostA.uucp, the LHS matches, causing it to
be rewritten as hostA!joe@mailhost.
See Section 23.4.2 for a full description of how
$@ is used in this way.