hostmerge.sh

#!/usr/bin/env bash

HEADER="
127.0.0.1 localhost

# The following lines are desirable for IPv6 capable hosts
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
"

TEMPHOSTS=$( tempfile -p hosts )

for f in "$@"; do
    grep -Eo '^[^#]*$' "$f" |\
        sed -e 's/^[ \t]\+//' |\
        sed -e 's/[ \t]\+$//' |\
        grep -Eo '^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\s+(([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9])$' |\
        awk '{print $1, $2}' |\
        sort >> $TEMPHOSTS
done

FINAL=$( tempfile -p hosts )

echo 127.0.1.1 $(hostname) > $FINAL
cat >> $FINAL <<EOL
$HEADER
EOL

echo '' >> $FINAL
sort "$TEMPHOSTS" | uniq >> $FINAL

sudo cp $FINAL /etc/hosts
sudo chmod 644 /etc/hosts

rm $TEMPHOSTS $FINAL