A.2 Sourcing libraries at run–time ¶

To source a library at run–time, we have to first embed the linker library; Embedding the linker library. The linker library visits the file systems searching for MBFL library files in a list of directories.

The linker library defines a default search path containing the following directories:

/usr/local/share/mbfl
/usr/share/mbfl
/share/mbfl

We can define a search path, which takes precedence over the default one, by exporting the environment variable MBFL_LIBRARY_PATH. For example, we can put the following line in a ~/.bash_profile file:

export MBFL_LIBRARY_PATH=/home/marco/share/mbfl

Once the search path is configured, we start a script with the following preprocessor macro uses:

mbfl_embed_library(__LIBMBFL_LINKER__)
mbfl_linker_source_library_by_stem(core)

the use of macro mbfl_linker_source_library_by_stem() expands into code that will search a library whose file name is built from the “stem” ‘core’ as follows:

printf -v FILENAME 'libmbfl-%s.bash' "$STEM"

in this case the result is libmbfl-core.bash; if the library is found: it is loaded using mbfl_load_library(); if the library is not found: the script exits with exit_because_error_loading_library().

We can insert uses of mbfl_linker_source_library_by_stem() to load all the libraries we need:

mbfl_linker_source_library_by_stem(git)
mbfl_linker_source_library_by_stem(passwords)
mbfl_linker_source_library_by_stem(containers)

If a library with a specific stem has already been loaded: nothing happens. In the following code:

mbfl_linker_source_library_by_stem(containers)
mbfl_linker_source_library_by_stem(containers)

the first use of mbfl_linker_source_library_by_stem() will source the library, the second use will do nothing.