The first thing you want to do is to verify that you can connect using SQL*Plus. It's a an invalualble tool for allowing you to check if the database is allowing remote connections

At a UNIX shell prompt:

$ORACLE_HOME/bin/sqlplus uname@ihr-live/password
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where $ORACLE_HOME is an environment variable that should already be set to the top level Oracle directory, uname is the actual Oracle database user you want, and password is the Oracle database password for that user

If that checks out, you can use this as code:

$ENV{'ORACLE_HOME'} = '/path/to/oracle';
$ENV{'ORACLE_SID'}  = 'IHRLIVE';
$dbh = DBI->connect('DBI:Oracle:', $uname, $password,
                    {
                    PrintError => 0,
                    RaiseError => 0
                    });
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