Question

I’m looking for some tips to implement binary --version that would provide good information about the version it was compiled from.

The project is using autotools build system, and is stored in a git repo that acts as a SVN frontend.

What I would like to have inside the binary is:

• compilation time
• SVN commit that acts as base
• last git commit ID and time
• if possible the last commit that affects this specific binary

Answer 1

You’ll probably want to write your source code to use a #defined constant version string. You can then pass that in through your build with a -DMY_VERSION=... option. That’ll let you embed a default value in the code, too, wrapped in an #ifndef, just in case!

#ifndef MY_VERSION
#define MY_VERSION 0.0.1-alpha
#endif

print_version() {
    printf("my product: %s\n", MY_VERSION);
}

A nice way to handle this on the build process side to make an intermediate build product which is simply a makefile snippet like MY_VERSION = "...". This again adds redundancy by letting you distribute the project with the version file already created, so that the build doesn’t have to depend on the presence of the SCM.

You can then create the version string however you like, for example:

echo -n 'MY_VERSION = "' > VERSION_FILE
git describe >> VERSION_FILE
echo "Compiled on $(date)" >> VERSION_FILE
...
echo '"' >> VERSION_FILE

Then in your primary makefile, include that snippet, and add -DMY_VERSION='"$(MY_VERSION)"' to the build flags for the appropriate object.

A slight variation: make your generated file purely the version string, then pull that value into the appropriate variable in the makefile.

If you need help with specific git commands to get the desired output, feel free to comment. git describe is a great one, though, meant for exactly this kind of thing. The default output is the closest tag ancestor of the current commit, hyphen, number of commits since the tag, hyphen, and abbreviated commit hash.