If you want to see what a name expands into, you can use the builtin
dumpdef:
Accepts any number of arguments. If called without any arguments, it displays the definitions of all known names, otherwise it displays the definitions of the names given. The output is printed to the current debug file (usually standard error), and is sorted by name. If an unknown name is encountered, a warning is printed.
The expansion of dumpdef is void.
$ m4 -d define(`foo', `Hello world.') ⇒ dumpdef(`foo') error→foo: ⇒ dumpdef(`define') error→define: ⇒
The last example shows how builtin macros definitions are displayed. The definition that is dumped corresponds to what would occur if the macro were to be called at that point, even if other definitions are still live due to redefining a macro during argument collection.
$ m4 -d pushdef(`f', ``$0'1')pushdef(`f', ``$0'2') ⇒ f(popdef(`f')dumpdef(`f')) error→f: ⇒f2 f(popdef(`f')dumpdef(`f')) error→m4:stdin:3: undefined macro `f' ⇒f1
See Debug Levels, for information on controlling the details of the display.