Give 3 servers s1.perlmaven.com, s2.perlmaven.com, and s3.perlmaven.com

rex -H s1.perlmaven.com -e 'say for run q(uptime)'
rex -H 's1.perlmaven.com s2.perlmaven.com s3.perlmaven.com' -e 'say for run q(uptime)'
rex -H 's[1,2,3].perlmaven.com' -e 'say for run q(uptime)'
rex -H 's[1..3].perlmaven.com' -e 'say for run q(uptime)'
rex -H 's[1..3].perlmaven.com' -e 'my $out = run q(uptime);  say scalar reverse $out'
rex -H 's[1..3].perlamven.com' -e 'say for run q(df -h)'

Given just IP addresses

rex -u root -H '104.248.57.39 104.248.53.65' -e 'say for run q(hostname)'

I could also edit vim ~/.ssh/config and add the following:

Host d1
    Hostname 104.248.57.39
Host d2
    Hostname 104.248.53.65

Host d*
    User root

Then I can use:

rex -H 'd[1..2]' -e 'say for run q(hostname)'