For C header files, you can prevent multiple inclusion of a header file like:
#ifndef MY_FOO_H
#define MY_FOO_H
[...]
#endif
How can I do the same thing in m4 such that multiple include() macro calls to the same file will only cause the contents to be included once?
Specifically, I want to do an ifdef guard that involves using macro changequote ( I'll not clutter my code with dnl's):
Originally, when I do the following, multiple inclusions still corrupts the quotes:
changequote_file.m4:
ifdef(my_foo_m4,,define(my_foo_m4,1)
changequote([,])
)
changequote_invocation.m4:
include(changequote_file.m4)
After first include invocation:
[I should not have brackets around me]
`I should have normal m4 quotes around me'
include(changequote_file.m4)
After second include invocation:
[I should not have brackets around me]
`I should have normal m4 quotes around me'
Invoked with m4 changequote_invocation.m4 yields:
After first include invocation:
I should not have brackets around me
`I should have normal m4 quotes around me'
After second include invocation:
[I should not have brackets around me]
`I should have normal m4 quotes around me'
The most straightforward way is an almost-literal translation of the cpp version:
ifdef(`my_foo_m4',,`define(`my_foo_m4',1)dnl
(rest of file here)
')dnl
So if my_foo_m4 is defined, the file expands to nothing, otherwise its contents are evaluated.