The dnl command can also be used to put comments into an mc file. Just be sure to
put a blank line after the last dnl because each dnl gobbles both the text and the
newline:
dnl This is a comment.
?†? note the extra blank line
17.1.3 m4 and Arguments
When an m4 macro name is immediately followed by a left parenthesis, it is treated
like a function call. Arguments given to it in that role are used to replace $digit
expressions in the original definition. For example, suppose the m4 macro CONCAT
is defined like this:
define(`CONCAT??,`$1$2$3??)dnl
and then later used like this:
CONCAT(`host??, `.??, `domain??)
The result will be that the host will replace $1, the dot will replace $2, and the domain
will replace $3, all jammed tightly together just as '$1$2$3' were:
host.domain
Macro arguments are used to create suchtech niques as FEATURE( ) and OSTYPE( ),
which are described later in this chapter.
17.1.4 The DOL m4 Macro
Ordinarily, the $ character is interpreted by m4 as a special character when found
inside its define expressions:
define(`A??, `$2??)
?†‘
the $ makes $2 an m4 positional variable
There might be times, however, when you might want to put a literal $ character into
a definition??”perhaps when designing your own DOMAIN, FEATURE, or HACK
files.
You place a literal $ into a definition with the DOL m4 macro.
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