RPM spec file - Is it possible to dynamically populate a spec file variable

Question

I have a spec file. I need to %define a spec variable that gets its value from a one line file on the system.

For example

%define path `cat /home/user/path_file` 

and in path_file is one line

/var/www/html/hosts 

This partially works. I say that begins in the RPM BUILD output sometimes the value of ${path} is literally my command cat /home/user/path_file and sometimes the value is the line in the path_file (/var/www/html/hosts) as it should be?

Answer 1

You can define rpmbuild variables with %(cmd) at the top of the spec file. Notice the command is in parenthesis, not curly brackets. An example:

%define whoami %(whoami) 

And elsewhere in the spec file, such as a script or the build/install sections, use the variable as normal in the curly brackets like this:

echo "The user that built this is %{whoami}" 

The cmd can be anything, including your cat command. Be careful - when another user rebuilds the spec file it may not find the file. So it'll be preferable to use the %{sourcedir} macro like this:

%define path %(cat %{sourcedir}/path_file) 

And make sure that path_file is in the source directory and included as a source in the spec file.