I found this m4 file in one of the open source projects.
changequote(«, »)dnl
include(«../defs.m4»)dnl
include(«tables.sql»)dnl
include(«functions.sql»)dnl
include(«triggers.sql»)dnl
include(«api.sql»)dnl
What is m4?
Is it the GNU M4 or something else?
Precisely so. M4 is a macro-processor.
This particular file includes five other files, which are, in turn, will be used as a list of instructions for processor. The resulting ouput will be sent to stdout.