Macros can have arguments. The nth argument is denoted by
$n in the expansion text, and is replaced by the nth actual
argument, when the macro is expanded. Here is a example of a macro with
two arguments. It simply exchanges the order of the two arguments.
define(`exch', `$2, $1') => exch(arg1, arg2) =>arg2, arg1
This can be used, for example, if you like the arguments to
define to be reversed.
define(`exch', `$2, $1') => define(exch(``expansion text'', ``macro'')) => macro =>expansion text
See section Quoting macro arguments, for an explanation of the double quotes.
GNU m4 allows the number following the `$' to consist of one
or more digits, allowing macros to have any number of arguments. This
is not so in UNIX implementations of m4, which only recognize
one digit.
As a special case, the zero'th argument, $0, is always the name
of the macro being expanded.
define(`test', ``Macro name: $0'') => test =>Macro name: test
If you want quoted text to appear as part of the expansion text, remember that quotes can be nested in quoted strings. Thus, in
define(`foo', `This is macro `foo'.') => foo =>This is macro foo.
The `foo' in the expansion text is not expanded, since it is a quoted string, and not a name.
Go to the first, previous, next, last section, table of contents.