The following script will extract all .define definitions and put them in a hash, where the keys are the names of the definitions and the values are the definition itself.

use strict;
use Data::Dumper ;

my %defines;
my $flag_in_define = 0;
my $name;

MAIN_LOOP: while (<DATA>) {
    if (m/^\.define (.*)/) {
        $flag_in_define = 1;
        $name = $1;
        next MAIN_LOOP;
    }
    if (m/^\.\./) {
        $flag_in_define = 0;
        next MAIN_LOOP;
    }
    if ($flag_in_define) {
        chomp;
        $defines{$name} .= $_;
        next MAIN_LOOP;
    }
}

print Dumper(\%defines);

__DATA__
rem ------------------------ book_tab variables ---------------------
.rem
.declare book_no                     a13
.declare l_code                      a10
.declare l_booking                   a12
.set page_no 1
.set first  "N"
.set no_more_clauses "N"
#dt 1 1 80 #
#dt 2 1 6 9 48 50 61 63 76 80 80 #
.define loktabs
        loc_table book_tab, book_hazmat, custdata2,   edit_table,
        book_rates, print_table in share update mode
..
.define get_input
        select key,  key1, key2,
               passkey3, passkey4, print_name
          into input_booking_seq, fax_header, file_no,
               input_print_rates, myNoteId, print_name
          from ed_table
         where ed_table.tag = 'BOOK'
           and ed_table.key = 'PRINT'
           and ed_table.user_id = user
..
.define get_user_info
        select  user_loc,user_name, user_company,
        into    user_location, user_name, user_company,
        from    sec_header
        where   user_id = lower(substr(user,5,10))
..

.execute lok_tabs
.execute get_user_info
[download]

You might wish to clean-up the definitions and remove multiple spaces.

Also note that it extracts all definitions not only those which start with "select".