To run a command on a bunch of servers, so you can say: spread.sh --command 'rm -rf / &' --grep-criteria '#centos|#msdos'

servers

#
# The format is following:
#     hostname:username:port:ssh-key #comments #tags
# All parameters besides of the first are optional
#
# Regular servers
host1
host2
host3
# The servers where we shall use an alternative username to log in
host4:user
# Servers where we shall use an alternative port to log in
host5::30022
host6:user:30022
# Servers where we shall use an alternative SSH-key to log in
host7:::~/.ssh/id_rsa.zaloopa
host8:user::~/.ssh/id_rsa.zaloopa
host9:user:30666:~/.ssh/id_rsa.zaloopa
# Servers we need to be found by some hashtags (so we can run the script with the -g parameter: "-g '#huerga'")
host10                                  #huerga
host11:user                             #huerga
host12:user:30022                       #huerga #zaebis #pizdets
host13:user:30022:~/.ssh/id_rsa.zaloppa #huerga #pizdets

spread.sh

#!/bin/bash

OPTS=$(getopt -n $(basename ${0}) -o c:g:y -l command:,grep-criterias:yes -- "${@}")
if [ "${?}" -ne 0 ]; then
        echo "Can't get options" >&2
        exit 1
fi
eval set -- "${OPTS}"
while :; do
        case "${1}" in
                -c|--command)
                        COMMAND="${2}"; shift 2;;
                -g|--grep-criterias)
                        CRITERIAS="${2}"; shift 2;;
                -y|--yes)
                        SURE="Y"; shift 1;;
                --)
                        shift; break;;
                *)
                        echo "Can't recognize the option: ${1}"; exit 1;;
        esac
done

TARGETS=$(cat ~/etc/servers | grep -E "${CRITERIAS}" | sed -e 's/[[:space:]]*#.*$//' -e '/^$/d')

if [ -z "${COMMAND}" ]; then
        echo "The command is undefined" >&2
        exit 1
fi

while :; do
        echo -e "Our targets are:\n${TARGETS}" >&2
        [ "${SURE}" != "Y" ] && read -p "Are you sure you want to run '${COMMAND}'? (Y/N) " SURE
        case "${SURE}" in
                [Yy])
                        for TARGET in ${TARGETS}; do
                                HOST=$(echo "${TARGET}" | sed -r -n -e 's/^([^:]+)(:([^:]*))?(:([^:]*))?(:([^:]*))?$/\1/gp')
                                USER=$(echo "${TARGET}" | sed -r -n -e 's/^([^:]+)(:([^:]*))?(:([^:]*))?(:([^:]*))?$/\3/gp')
                                PORT=$(echo "${TARGET}" | sed -r -n -e 's/^([^:]+)(:([^:]*))?(:([^:]*))?(:([^:]*))?$/\5/gp')
                                SKEY=$(echo "${TARGET}" | sed -r -n -e 's/^([^:]+)(:([^:]*))?(:([^:]*))?(:([^:]*))?$/\7/gp')
                                [ -z "${USER}" ] && USER=$(whoami)
                                [ -z "${PORT}" ] && PORT=22
                                [ -z "${SKEY}" ] && SKEY=~/.ssh/id_rsa
                                echo "Running '${COMMAND}' on ${HOST}:${PORT}..." >&2
                                ssh -i "${SKEY}" -p "${PORT}" -l "${USER}" "${HOST}" "${COMMAND}"
                        done
                        break
                        ;;
                [Nn])
                        break
                        ;;
                *)
                        echo "So, Y or N?" >&2
                        ;;
        esac
done