$ /usr/bin/perl
use strict;
use warnings;
use DBI;
use DBD::DB2;
DBI->connect('DBI:DB2:viper', 'db2inst3', '');
__END__

DBI connect('viper','db2inst3',...) failed: Total Environment 
allocation failure!  Did you set up your DB2 client environment?

##</code><code>##

$ set | egrep '(DB2|INSTHOME)'
CUR_INSTHOME=/home/db2inst3
DB2DIR=/opt/ibm/db2/V9.5
DB2INSTANCE=db2inst3
INSTHOME=/home/db2inst3

##</code><code>##

$ db2 connect to viper

   Database Connection Information

 Database server        = DB2/LINUX 9.5.0
 SQL authorization ID   = DB2INST3
 Local database alias   = VIPER

$ db2 select CURRENT_TIMESTAMP from sysibm.sysdummy1

1
--------------------------
2008-04-24-15.00.39.518770

  1 record(s) selected.