#!/usr/bin/perl 
use strict;
use warnings;

my @header;

map {
    unless (/;$/)
    {   
        chomp;
        scalar @header == 2 and undef @header;
        scalar @header and $_ = ":$_";
        push @header, $_; 
    }   

    print @header, ":$_" if /;$/;

} <DATA>;

__DATA__
library_AND
PIN.A
DELAY_TABLE 1 20 2 40 3 60 4 65 5 75;
DELAY_TABLE 1 10 2 15 3 45 4 70 5 80;
POWER_TABLE 20 30 40 50 80 97 110 20;
POWER_TABLE 3 4 5 6 10 80 90 10 20;
library_BUF
PIN.B
LEAKAGE 1 2 3 4;
TRANSIT 1.1 2 3.4;