Bash script to update hostfile to mache docker-machines

docker-machine-hostnames.sh

#!/bin/bash

sethost () { # set up docker hostnames
    # replace everything in line with the right IP, with $IP $MACHINE
    D_MACHINE=$1
    echo "Update host file for machine=$D_MACHINE"

    DATE=$(date -u +%s)
    echo "backing up hosts to /tmp/hosts-$(date -u +%s)"
    cp /etc/hosts /tmp/hosts-$(date -u +%s)

    IP=$(docker-machine ip $D_MACHINE)
    if [ -n "$IP" -a -n "$D_MACHINE" ]; then

        OLD_LINE=$(egrep "\s$D_MACHINE$" /etc/hosts)
        OLD_LINES=$(egrep "\s$D_MACHINE$" /etc/hosts -c)
        NEW_LINE=$(sed "/\s$D_MACHINE$/ s/.*/$IP\t$D_MACHINE/g" /etc/hosts | egrep "\s$D_MACHINE$" )
        echo "change: $OLD_LINE => $NEW_LINE"

        # check we found one old line
        if [ $OLD_LINES -eq 1 ]; then
            # replace in file
            sudo sed -i "/\s$D_MACHINE$/ s/.*/$IP  $D_MACHINE/g" /etc/hosts
        else
            if [ $OLD_LINES -eq 0 ]; then
                # append to file
                sudo echo ""
                sudo sh -c "echo '$IP   $D_MACHINE' >> /etc/hosts" > /dev/null
            else
                echo "multiple lines found, aborting"
            fi
        fi
    else
        echo "D_MACHINE=$D_MACHINE or IP=$IP not found"
    fi
}

# update hostfile to point to named docker machines
for DMACHINE in $(docker-machine ls -q); do
    sethost $DMACHINE
done