recursively copy files with stripping prefix - linux

Question

I'm trying to create a GNU Makefile rule that copies files (found via VPATH) from one directory to another, preserving their directory structure.
There are zillions of ways to do this (starting with cp -r) but it seems that none of them work in the context of make, where the copying is initiated in the target directory.
E.g.
cp ../src/foo.c ../src/bar.c .
All the source files share a common directory (only known at runtime), and this common directory should be stripped away.
E.g.
$ srcdir=../../knurgl
$ cp ${srcdir}/src/foo.c ${srcdir}/src/bar.c .
$ find . -type f
./src/foo.c
./src/bar.c
even though the common directory is known at runtime, it can be arbitrary and even include the current directory . (in which case the operation should be a nop).
This is what i tried:
cp
cp --parent ${srcdir}/src/foo.c ${srcdir}/src/bar.c .
but rightfully this refuses to work when called from the target directory (as it would always copy the files onto themselves).
tar
tar c ${srcdir}/src/foo.c ${srcdir}/src/bar.c | tar x
this strips away any relative directories, but keeps the rest (so I end up with ./knurgl/src/foo.c instead of ./src/foo.c.
The --strip-components option doesn't help me much, as i don't know the depth of ${srcdir}.

Answer 1

Instead of
cp --parent ${srcdir}/src/foo.c ${srcdir}/src/bar.c .
(which doesn't work because it doesn't strip $srcdir) you can write
(wd=$PWD; cd $srcdir; cp --parent src/foo.c src/bar.c $wd)

Answer 2

make has built-in functions for handling strings. To replace old_base_dir with new_base_dir in the variable path, call:
$(path:old_base_dir/%=new_base_dir/%)
You can also let it perform the substitution on a list:
$(foreach path,$(path_list),$(path:old_base_dir/%=new_base_dir/%)
Here, the variable path_list contains multiple files. Note though that this will break if the file names contain spaces.
The manual of GNU make describes many more useful functions.