Shell Programming and Scripting

$ cat ssh.sh

#!/bin/bash

MAXPROCS=2
PROCS=$(seq 1 $MAXPROCS)

function ssh_hosts # Reads hosts from stdin, writes output to stdout
{
        while read HOST
        do
                ssh "$HOST" printf "$HOST" ';' uptime </dev/null
        done
}

# Loop until we run out of lines
while [ -z "$FINISHED" ]
do
        # Read a line for each thread and feed it into the right file
        for N in $PROCS
        do
                if read LINE
                then
                        echo "$LINE">>/tmp/$$-$N
                        continue
                fi

                FINISHED=1
                break
        done
done < hosts1

for N in $PROCS
do
        # Add these to the list of tempfiles to delete on exit
        FILES="$FILES /tmp/$$-out$N /tmp/$$-$N"

        # Make a process reading from /tmp/$$-$N and writing to /tmp/$$-out$N
        ssh_hosts < /tmp/$$-$N > /tmp/$$-out$N &
done

# Delete all temporary files on exit, even if we quit with ctrl-c
trap "rm -f $FIFOS $FILES" EXIT

wait    # Wait for readers to quit

cat /tmp/$$-out*      # Read all output to stdout

$ cat hosts1

172.16.0.154
172.16.0.62
172.16.0.222
172.16.0.182
172.16.0.90
172.16.0.226
172.16.0.118
172.16.0.158
172.16.0.50
172.16.0.130
172.16.0.86

$ ./ssh.sh

172.16.0.154 11:10:32 up 6 days, 21:36,  0 users,  load average: 0.01, 0.02, 0.00
172.16.0.222 11:18:44 up 15 days, 21:26,  0 users,  load average: 0.03, 0.03, 0.00
172.16.0.90 10:50:28 up 2 days, 26 min,  0 users,  load average: 0.06, 0.04, 0.00
172.16.0.118 11:04:55 up 12 days, 23:12,  0 users,  load average: 0.11, 0.07, 0.02
172.16.0.50 10:51:34 up 47 days, 19:47,  0 users,  load average: 0.04, 0.04, 0.00
172.16.0.86 11:02:14 up 22 days,  1:52,  0 users,  load average: 0.01, 0.01, 0.00
172.16.0.62 11:24:51 up 21 days,  2:27,  0 users,  load average: 0.00, 0.00, 0.00
172.16.0.182 10:15:50 up 2 days, 25 min,  0 users,  load average: 0.02, 0.04, 0.00
172.16.0.226 11:17:48 up 6 days, 21:37,  0 users,  load average: 0.00, 0.00, 0.00
172.16.0.158 11:21:46 up 2 days, 24 min,  0 users,  load average: 0.08, 0.02, 0.01
172.16.0.130 10:57:22 up 5 days, 19:42,  0 users,  load average: 0.00, 0.00, 0.00

$