(m4.info)Pseudo Arguments


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5.3 Special arguments to macros
===============================

There is a special notation for the number of actual arguments supplied,
and for all the actual arguments.

   The number of actual arguments in a macro call is denoted by `$#' in
the expansion text.

 -- Composite: nargs (...)
     Expands to a count of the number of arguments supplied.

     define(`nargs', `$#')
     =>
     nargs
     =>0
     nargs()
     =>1
     nargs(`arg1', `arg2', `arg3')
     =>3
     nargs(`commas can be quoted, like this')
     =>1
     nargs(arg1#inside comments, commas do not separate arguments
     still arg1)
     =>1
     nargs((unquoted parentheses, like this, group arguments))
     =>1

   Remember that `#' defaults to the comment character; if you forget
quotes to inhibit the comment behavior, your macro definition may not
end where you expected.

     dnl Attempt to define a macro to just `$#'
     define(underquoted, $#)
     oops)
     =>
     underquoted
     =>0)
     =>oops

   The notation `$*' can be used in the expansion text to denote all
the actual arguments, unquoted, with commas in between.  For example

     define(`echo', `$*')
     =>
     echo(arg1,    arg2, arg3 , arg4)
     =>arg1,arg2,arg3 ,arg4

   Often each argument should be quoted, and the notation `$@' handles
that.  It is just like `$*', except that it quotes each argument.  A
simple example of that is:

     define(`echo', `$@')
     =>
     echo(arg1,    arg2, arg3 , arg4)
     =>arg1,arg2,arg3 ,arg4

   Where did the quotes go?  Of course, they were eaten, when the
expanded text were reread by `m4'.  To show the difference, try

     define(`echo1', `$*')
     =>
     define(`echo2', `$@')
     =>
     define(`foo', `This is macro `foo'.')
     =>
     echo1(foo)
     =>This is macro This is macro foo..
     echo1(`foo')
     =>This is macro foo.
     echo2(foo)
     =>This is macro foo.
     echo2(`foo')
     =>foo

Note: Trace, if you do not understand this.  As another example of the
difference, remember that comments encountered in arguments are passed
untouched to the macro, and that quoting disables comments.

     define(`echo1', `$*')
     =>
     define(`echo2', `$@')
     =>
     define(`foo', `bar')
     =>
     echo1(#foo'foo
     foo)
     =>#foo'foo
     =>bar
     echo2(#foo'foo
     foo)
     =>#foobar
     =>bar'

   A `$' sign in the expansion text, that is not followed by anything
`m4' understands, is simply copied to the macro expansion, as any other
text is.

     define(`foo', `$$$ hello $$$')
     =>
     foo
     =>$$$ hello $$$

   If you want a macro to expand to something like `$12', the judicious
use of nested quoting can put a safe character between the `$' and the
next character, relying on the rescanning to remove the nested quote.
This will prevent `m4' from interpreting the `$' sign as a reference to
an argument.

     define(`foo', `no nested quote: $1')
     =>
     foo(`arg')
     =>no nested quote: arg
     define(`foo', `nested quote around $: `$'1')
     =>
     foo(`arg')
     =>nested quote around $: $1
     define(`foo', `nested empty quote after $: $`'1')
     =>
     foo(`arg')
     =>nested empty quote after $: $1
     define(`foo', `nested quote around next character: $`1'')
     =>
     foo(`arg')
     =>nested quote around next character: $1
     define(`foo', `nested quote around both: `$1'')
     =>
     foo(`arg')
     =>nested quote around both: arg


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