Multi-host execution util.

README.md

The script assumes:

a) you have something like defined:

export maindev=maindev
export bkupdev=bkupdev
export mainstg=mainstg
export bkupstg=bkupstg
export mainprod=mainprod
export bkupprod=bkupprod
export alldev="maindev bkupdev"
export allstg="mainstg bkupstg"
# Expansion is not recursive, can't use alllow="alldev allstg" here.
export alllow="maindev bkupdev mainstg bkupstg"

where the identify definitions are needed for dereferencing later, and, in .ssh/config

Host maindev
HostName dev.example.com
User me_who_else

Host bkupdev
HostName dev-reserve.example.com
User me_who_else

Then on alldev uname -n returns:

## On maindev: uname -n
dev.example.com     maindev
## On bkupdev: uname -n
dev-reserve.example.com     bkupdev

column -t is helpful for cleaning up output.

on -n will not append the host alias to each line of output.

on "host01 hostgroupB" will drop the user into a shell on each host in sequence.

on.sh

#!/usr/bin/bash

SHOW_HOST=1
if [ "$1" == "-n" ]; then
    shift
    SHOW_HOST=""
fi

ON="$1"
shift

for TARGET in ${ON}; do
    for HOST in ${!TARGET}; do
        echo "## On $HOST: $@" >/dev/stderr
        if [[ "x$@" == "x" ]]; then  # No command, shell into each host.
            ssh $HOST
        elif [ -z "$SHOW_HOST" ]; then  # -n - don't append host name to output
            # First sed rule drops a long banner msg.
            ssh $HOST $@ 2>&1 | sed -En '/^(In proceeding|1\) you are)/ d; p'
        else  # Append host name to each line of output.
            ssh $HOST $@ 2>&1 | sed -En '/^(In proceeding|1\) you are)/ d; s/$/\t'$HOST'/; p'
        fi
    done
done