1.2 Reliable run–time loading

A more reliable way to load the library is:

declare mbfl_INTERACTIVE=no
declare mbfl_LOADED=no
declare mbfl_HARDCODED=
declare mbfl_INSTALLED=$(type -p mbfl-config &>/dev/null && mbfl-config) &>/dev/null

declare item
for item in "$MBFL_LIBRARY" "$mbfl_HARDCODED" "$mbfl_INSTALLED"
do
    if test -n "$item" -a -f "$item" -a -r "$item"
    then
        if source "$item" &>/dev/null
        then
	    declare -r mbfl_LOADED_LIBRARY=$item
	    break
        else
            printf '%s error: loading MBFL file "%s"\n' "$script_PROGNAME" "$item" >&2
            exit 100
        fi
    fi
done
unset -v item
if test "$mbfl_LOADED" != yes
then
    printf '%s error: incorrect evaluation of MBFL\n' "$script_PROGNAME" >&2
    exit 100
fi

where the value of mbfl_HARDCODED can be the pathname of a known location in which to find the library. This code:

1. Looks for the pathname in the MBFL_LIBRARY variable, to allow us to explicitly select the file from the command line; example:

   $ MBFL_LIBRARY=/path/to/libmbfl.sh script.sh
   

2. Looks in some known directory; for example a subdirectory of a software package that we have distributed.
3. As a last resort tries to evaluate the mbfl-config script to pick up a library installed on the system.

We see that the output of the source command is discarded: this is because we assume that:

• If an error occurs evaluating the library a lot of error messages may fill the screen, confusing the user; we just want a single error message pointing the finger of blame.
• An error in the evaluation of the library code can be replicated because the evaluation does not heavily depend on the environment, so we can track down library errors later.

This code is included in the MBFL distribution in the src/lib/loader.sh file; we can also automatically include it in a script with the preprocessor macro mbfl_library_loader.

This document describes version 3.0.0-devel.0 of Marcos Bash Functions Library.