My work is converting Linux command into CMake execute_process(COMMAND ...), and there are some differences between them, so i need to understand each Linux command. But this m4 command really beat me. The m4 command as below:
m4 -Isource/analyzer/ -P < source/analyzer/aParser.m4y > source/analyzer/aParser.by
What does this command mean?
I have read m4 document before, and it said the format of the m4 command is: m4 [option…] [file…], so i think in command:
m4 -Isource/analyzer/ -P < source/analyzer/aParser.m4y > source/analyzer/aParser.by
the -Isource/analyzer/ -P is [option...] of m4, and this m4 commad use<to read the file source/analyzer/aParser.m4y as m4 [file...], did i understand right?
m4 is a macro processor. Read its documentation (for GNU m4). It is a quite complex thing, so I won't try to abstract it in a few sentences.
The -P option is prefixing builtins with m4_ so define becomes m4_define etc...
The < (and >) is not an option to m4, it is a general shell redirection.
Of course, you also need to study the documentation of cmake (which I personally don't like much, since GNU make 4 is powerful enough without cmake)
You probably should spend weeks in reading documentations, including Advanced Bash Scripting guide & Advanced Linux Programming (and the other documentations I pointed here).