#! perl -slw
use strict;

sub other{ print "Processing '$_[0]' with arg: '$_[1]'" }

my %dispatch = map{ $_ => \&other } 'b'..'z';
$dispatch{a} = sub {
    print "\nNew section\nProcessing 'a' with arg '$_[1]'";
};

while( <DATA> ) {
    chomp;
    $dispatch{$1}->( $1, $2 )
        while m/ \] ( [a-z] ) \[ ( [^]]+ ) /xg;
}

__DATA__
...