InstallTargets

It's often useful to be able to run scons install to copy built programs and shared libraries to another location, such as a project common area for testing, or perhaps the their final location in the filesystem. "install" is a familiar phony target in other build systems (a phony target is one that does not build a file indicated by its name, but instead causes some other work to be done). SCons can set up phony targets using the Alias function. Here's one way to do that:

prefix = "/usr/local"

someshlib = env.SharedLibrary('foo', "foo.c")
someprogram = env.Program("fooprog", "fooprog.c")

# the install target
env.Alias("install", env.Install(os.path.join(prefix, "lib"), someshlib))
env.Alias("install", env.Install(os.path.join(prefix, "bin"), someprogram))

Basically we alias 'install' to a couple of Install nodes, returned by the Install method. That's all. Alias is additive, so this works fine. There is no need to add something like Depends(install, someshlib), since SCons computes that dependency automatically.

Now

$ scons install

will do the work defined by the install target. The installs won't happen if you just invoke SCons without arguments, since by default, SCons acts only on targets underneath the starting directory, which /usr/local is unlikely to be. This choice of avoiding out-of-tree actions by default is intentional, as they're normally less common operations, and the default should reflect the most common work. Of course, scons lets you redefine what the default behavior is if you don't agree, just use the Default function.

If you need some finer-grained install targets, you could use something like this:

Alias('install-lib', Install(os.path.join(prefix, "lib"), ...))
Alias('install-bin', Install(os.path.join(prefix, "bin"), ...))
Alias('install', ['install-bin', 'install-lib'])

Permissions

Question: how to set permissions properly (binaries get 755, headers get 644, etc.) after an install?

• One way to do it is to monkey-patch scons to create a method that acts like Install but takes an additional permission argument. Wrappers with predefined permissions are useful for cleaner markup:

import SCons

# define the custom function
from SCons.Script.SConscript import SConsEnvironment
SConsEnvironment.Chmod = SCons.Action.ActionFactory(os.chmod,
        lambda dest, mode: 'Chmod("%s", 0o%o)' % (dest, mode))

def InstallPerm(env, dest, files, perm):
    obj = env.Install(dest, files)
    for i in obj:
        env.AddPostAction(i, env.Chmod(str(i), perm))
    return dest

# put this function "in" scons
SConsEnvironment.InstallPerm = InstallPerm

# great, we're ready to use it!
env.InstallPerm(bindir, ['fooprog', 'barprog'], 0o755)

# but let's say we're not happy yet, we'd prefer nicer names.
SConsEnvironment.InstallProgram = lambda env, dest, files: InstallPerm(env, dest, files, 0o755)
SConsEnvironment.InstallHeader = lambda env, dest, files: InstallPerm(env, dest, files, 0o644)

# great, now you can also install by calling a method named 'InstallHeader' or 'InstallProgram'!
env.InstallHeader(incdir, ['foo.h', 'bar.h'])

Don't forget to set the umask, or created directories might get wrong permissions on Unix and Windows:

try:
    umask = os.umask(0o022)
    print('setting umask to 0o022 (was 0o%o)' % umask)
except OSError:     # ignore on systems that don't support umask
    pass

Note that it's considered bad Python form to assign names to lambdas and a code checker like pylint would complain, but it will work nonetheless.

• Another similar method to install data with correct permissions is to use a Command :

source="./data/icon.png"
target="/usr/local/share/X/icon.png"

env.Alias("install", target)
env.Command(target, source, [
            Copy("$TARGET","$SOURCE"),
            Chmod("$TARGET", 0o664),
])

where target and source could be set in a directory parsing loop for conveniance :

# where you need to implement 'RecursiveGlob' yourself 
for file in RecursiveGlob("./data", "*"):
    # strip 'data/' out to have the filepath relative to data dir
    index = file.find("data/") + len("data/")
    filename_relative = file[index:]
    source = os.path.join("./data", filename_relative)
    target = os.path.join(data_dir, filename_relative)
            
    env.Alias("install", target)
    env.Command(target, source, [
                Copy("$TARGET","$SOURCE"),
                Chmod("$TARGET", 0664),
    ])

For best results, also make sure the umask is set as described above.

Locale files

Installing locale files on UNIX systems can be a little tricky :

This is an example that will handle installing .mo files for a source layout of /po/[language code]/app_name.mo.

# install .mo files
locale_dir = "/usr/local/share/locale"

mo_files = Glob("./po/*/app_name.mo",strings=True)
for mo in mo_files:
    # extract language code
    index_lo = mo.find("po/") + len("po/")
    index_hi = mo.find("/app_name.mo")
    lang_name = mo[index_lo:index_hi]
    # copy file
    install_location = locale_dir + "/" + lang_name + "/LC_MESSAGES/app_name.mo"
    env.Alias("install", env.InstallAs(install_location, mo))

It should be simple enough to adapt this code to layouts like /po/[language code].mo or any other.

Uninstall targets

Here's a sample uninstall function :

def create_uninstall_target(env, path, is_glob):
    if is_glob:
        all_files = Glob(path,strings=True)
        for filei in all_files:
            env.Command("uninstall-"+filei, filei, [
                        Delete("$SOURCE"),
            ])
            env.Alias("uninstall", "uninstall-"+filei)   
    else:
        env.Command("uninstall-"+path, path, [
                    Delete("$SOURCE"),
        ])
        env.Alias("uninstall", "uninstall-"+path)  

You can use it like this :

if 'uninstall' in COMMAND_LINE_TARGETS:
    # create uninstall targets
    create_uninstall_target(env, "/usr/local/bin/myapp", False)
    create_uninstall_target(env, "/usr/local/share/myapp/", False)
    create_uninstall_target(env, "/usr/local/share/locale/*/LC_MESSAGES/myapp.mo", True)

If you want to uninstall all the files installed using Install or InstallAs, there is a more expeditive way:

env.Command("uninstall", None, Delete(FindInstalledFiles()))