24_install_target

Lesson 24 -- install Target

What you'll learn

How to write install and uninstall targets that copy built artifacts to standard system directories, using the conventions that package builders expect.

The install command

You might wonder why install rules use the install command instead of cp. Three reasons:

1. Permissions in one step -- install -m 755 greeter /usr/local/bin/ copies the file and sets it executable atomically.
2. Directory creation -- install -d /usr/local/bin creates the directory (and parents) if it doesn't exist, like mkdir -p.
3. Convention -- every Unix Makefile uses install. Package build systems (dpkg-buildpackage, rpmbuild, brew) expect it.

install -m 755 $(TARGET) $(DESTDIR)$(BINDIR)   # executable: rwxr-xr-x
install -m 644 $(LIB) $(DESTDIR)$(LIBDIR)      # library:    rw-r--r--
install -m 644 include/greet.hpp $(DESTDIR)$(INCDIR)  # header: rw-r--r--

Directory conventions

Variable	Default	Contents
PREFIX	/usr/local	Base directory for all installed files
BINDIR	$(PREFIX)/bin	Executables
LIBDIR	$(PREFIX)/lib	Static and shared libraries
INCDIR	$(PREFIX)/include	Public headers (often in a subdirectory like include/greetlib/)

PREFIX is declared with ?= so users can override it:

make install PREFIX=/opt/myapp

This installs to /opt/myapp/bin/, /opt/myapp/lib/, etc.

DESTDIR -- staged installs

DESTDIR is not the same as PREFIX. It is a staging root prepended to every path, used by package builders to install into a temporary directory tree without touching the real filesystem.

make install DESTDIR=/tmp/staging

This creates:

/tmp/staging/usr/local/bin/greeter
/tmp/staging/usr/local/lib/libgreet.a
/tmp/staging/usr/local/include/greetlib/greet.hpp

The package builder then wraps that tree into a .deb, .rpm, or similar. The final user installs the package, which unpacks into the real /usr/local/.

The key difference: PREFIX affects the runtime paths baked into the software. DESTDIR only affects where files land during make install -- the software still thinks it lives at PREFIX.

uninstall target

The uninstall target removes exactly what install put in place:

uninstall:
	rm -f $(DESTDIR)$(BINDIR)/$(notdir $(TARGET))
	rm -f $(DESTDIR)$(LIBDIR)/$(notdir $(LIB))
	rm -f $(DESTDIR)$(INCDIR)/greet.hpp
	-rmdir $(DESTDIR)$(INCDIR) 2>/dev/null || true

The -rmdir at the end removes the greetlib/ subdirectory, but only if it's empty. The leading - tells Make to ignore the error if the directory isn't empty (other software may have installed headers there too). The || true ensures the shell exit code is zero regardless.

File manipulation functions

The uninstall target uses $(notdir) to strip the directory prefix from a path. Make provides four path-dissection functions:

Function	Input	Output	Use case
$(notdir path)	build/greeter	greeter	Get the filename for install/uninstall
$(dir path)	build/greeter	build/	Get the directory part (includes trailing /)
$(basename path)	build/greeter	build/greeter	Strip the suffix (no .ext here, so unchanged)
$(suffix path)	build/libgreet.a	.a	Get the file extension

Run make debug to see these in action with the actual values from this Makefile.

How CMake replaces this

CMake has built-in install support that handles PREFIX, DESTDIR, permissions, and platform differences automatically:

install(TARGETS greeter DESTINATION bin)
install(TARGETS greet ARCHIVE DESTINATION lib)
install(FILES include/greet.hpp DESTINATION include/greetlib)

Running cmake --install build --prefix /opt/myapp does the equivalent of make install PREFIX=/opt/myapp. CMake also generates an uninstall target and handles RPATH fixup for shared libraries.

Try it

cd 24_install_target
make                                        # build the executable and library
./build/greeter World                       # test it locally
make debug                                  # see path functions and install paths

make install PREFIX=/tmp/test_install       # install to a safe location
ls /tmp/test_install/bin/                   # greeter is there
ls /tmp/test_install/lib/                   # libgreet.a is there
ls /tmp/test_install/include/greetlib/      # greet.hpp is there
/tmp/test_install/bin/greeter Make          # run from installed location

make uninstall PREFIX=/tmp/test_install     # clean up
rm -rf /tmp/test_install                    # remove the test directory
make clean

Files

File	Purpose
include/greet.hpp	Declares greet() -- the public header installed to INCDIR
src/greet.cpp	Implements greet() -- compiled into libgreet.a
src/main.cpp	CLI entry point -- compiled into the greeter executable
Makefile	Demonstrates install, uninstall, DESTDIR, PREFIX, and path functions