How can I query prerequisites of a target from a GNU Make makefile?
E.g. if the targets specified like this:
fred: wilma barney betty
I want to print prerequisites of
fred like this:
$ make some_action fred wilma barney betty
Maybe a dry run is what you are looking for?
make --dry-run fred
The man page gives us this about the dry run:
-n, --just-print, --dry-run, --recon Print the commands that would be executed, but do not execute them.
So it will not give you a direct list, but a indirect list since you know that he would like to execute what he depends on.
Another possibility, though one that gives you tons more info than you want, is the "print database" option. From the manual:
‘-p’ ‘--print-data-base’ Print the data base (rules and variable values) that results from reading the makefiles; then execute as usual or as otherwise specified. This also prints the version information given by the ‘-v’ switch (see below). To print the data base without trying to remake any files, use ‘make -qp’. To print the data base of predefined rules and variables, use ‘make -p -f /dev/null’. The data base output contains file name and line number information for recipe and variable definitions, so it can be a useful debugging tool in complex environments.
Fair warning, though: sifting through this mess will be brutal without some post-processing.
Let's say your Makefile is this:
.PHONY: wilma barney betty
fred: wilma barney betty
The latest version of remake has a
--profile option which outputs data that can be turned into a graph of the dependencies checked. The data file output format is what callgrind uses, so another program is needed to produce the graphs from the data that is output. See https://github.com/rocky/remake/tree/master/profile
In an older version of remake, here is how you could get the dependencies using
$ remake -X -f Makefile GNU Make 4.1+dbg0.91 Built for x86_64-unknown-linux-gnu Copyright (C) 1988-2014 Free Software Foundation, Inc. Copyright (C) 2015 Rocky Bernstein. License GPLv3+: GNU GPL version 3 or later This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Reading makefiles... Updating makefiles.... Updating goal targets.... File 'fred' does not exist. File 'wilma' does not exist. Must remake target 'wilma'. Successfully remade target file 'wilma'. <- (/tmp/??:0) wilma remake<0> target fred depend fred: wilma barney betty remake<1> quit remake: That's all, folks...
If you put those commands issued into a file, say
target fred depend
Then you can run:
cat cmds.txt | remake -X -f Makefile
I leave as an exercise how to do something more elaborate such as writing program that takes a dependency name and runs the above.