in reply to split file on blank lines and match blocks

trying to identify hosts that are members of the CRIT hostgroup, or of the DMZ hostgroup

Ignoring that your text say's that, and your code 'GRID|RMAN', this might set you on your road:

#! perl -slw
use strict;

$/ = ''; ## para model see perldoc -q paragraphs

m[
    (?=^.*(DMZ|CRIT))
    (?=^.*host_name\s+(\S+))
    (?=^.*address\s+(\S+))
]sx and print "$2 [$3] is a member of $1"
    while <DATA>;

__DATA__
[snip... your sample data here]

[download]

Produces:

C:\test>junk
denlas02 [146.xxx.xxx.xxx] is a member of DMZ
ppplas12 [10.50.33.26] is a member of CRIT

[download]
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In Section Seekers of Perl Wisdom