open( IN, $filename ) or die "$filename: $!";
{
    local $/ = '';  # cf. perldoc perlvar about $/ and "paragraph mode"

    while (<IN>)    # read a whole record into $_
    {
        @fields = split( /\](\w)\[/ ); # use parens to capture the letters
        shift @fields; # split puts an empty element before ']a[', so drop that

        my %record = @fields;  # convert array to key=>value hash

        # you now have tags as hash keys, strings as hash values:
        # $record{"a"}==1, $record{"b"}=="FORTUNE BAY", etc.
        # to use as you see fit.
    }
}