Example from Chapter 11 docs is incorrect?

[amine-aboufirass]

I'm trying to implement one of the examples in Chapter 11 of the manual as follows:

|   hello.c
|   SConstruct.py
|   
\---install-dir

SConstruct.py

env = Environment()
hello = env.Program('hello.c')
env.Install("#install-dir", hello)
env.Alias("install", "#install-dir")

hello.c

int main()
{
    printf("Hello, world!\n");
}

According to the manual, running scons -Q should only build the executable and not install it. Only when I specify scons -Q install should the executable be installed in install-dir:

This is an area where the Alias function comes in handy, allowing you, for example, to create a pseudo-target named install that can expand to the specified destination directory

However, in both cases where I use scons -Q and scons -Q install the executable gets installed. So I fail to see the purpose of env.Alias() in this example. What am I missing here?

[mwichmann]

This is all about target selection rules. If install evaluates to something in the project tree (i.e. at or below the directory of the SConstruct, which it is in your case), AND you haven't given any targets on the cmdline or called the Default function, then that target will be one selected for building. In the User Guide example, the directory to install to is /usr/bin/, which does not meet that selection rule, so it's not selected by default, only when you give the (alias) target on the cmdline.

[amine-aboufirass]

Thanks, you are correct, I changed the directory structure to:

+---dev
|       hello.c
|       SConstruct.py
|       
\---install-dir

and the SConstruct.py to

env = Environment()
hello = env.Program('hello.c')
env.Install("../install-dir", hello)
env.Alias("install", "../install-dir")

And now the behavior is as described by the docs.

[amine-aboufirass]

@mwichmann I do have a follow up question actually. I'm now trying with the InstallAs function to change the name of the installed file as follows:

# Change the name of the file upon installation

env = Environment()
hello = env.Program("hello.c")
env.InstallAs("../install-dir/hello-new", hello)
env.Alias("install", "../install-dir")

When I build with scons install it does copy the executable file but doesn't add the .exe extension to it (I'm on Windows). I'm wondering why that is? Isn't SCons supposed to be platform independent? For the time being I've had to change it to the following for the executable to work:

# Change the name of the file upon installation

env = Environment()
hello = env.Program("hello.c")
env.InstallAs("../install-dir/hello-new.exe", hello)
env.Alias("install", "../install-dir")

[mwichmann]

With InstallAs you're providing the new name to use, the builder takes that very literally. If you want to have it be somewhat independent, you can use the construction variables PROGSUFFIX and SHLIBSUFFIX. Since your destination is a "target" it will have command substitution applied to it (you can't use these everywhere, only in an appropriate context):

env.InstallAs("../install-dir/hello-new$PROGSUFFIX", hello)

See: https://scons.org/doc/production/HTML/scons-man.html#cv-PROGSUFFIX

To see what this is set to:

print("DEBUG: progsuffix is", env['PROGSUFFIX'])