@array = qw("User1 PS1 10.10.1.1","User2 PS2 10.10.1.2","User3 PS3 20.20.1.1","User4 PS4 20.20.1.2");

($ip[0] = $array[0]) =~ s/User1 PS1 (.+)/$1/;
($ip[1] = $array[3]) =~ s/User4 PS4 (.+)/$1/;

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

my @selection = qw/User1 User4/;
my $reg = join '|',@selection;
my @array = (
             'User1 PS1 10.10.10.1',
             'User2 PS2 10.10.10.2',
             'User3 PS3 10.10.10.3',
             'User4 PS4 10.10.10.4',
             );
my @ip = map { (split /\s+/)[-1] } grep(/^(?:$reg)/,@array);
local $, = "|\n";
print @ip;