Given the file path of a file has a hostname per line, looks up the IP for each host

filetoiplist.sh

#!/bin/sh

# *********************************************************************
# script: filetoiplist
# summary: given a file path (assuming it has a host per line), looks 
#	   up the IP for each host.
# dependencies: host; grep
# by: e.a.soto, [email protected]
# 
# history
# =======
# 
# 2015-09-16: created.
# 
# *********************************************************************

if [ $# -eq 0 ]
  then
    echo "File Path must be supplied!"
    exit 1
fi

# basic logic
# 
# use for to loop through each line in the file (which cat is reading)
#  does "host" command in each file which returns info on the host, including IP
# pipes to grep looking for the line with "has address" which has the IPv4 address
# pipes to cut, splitting on spaces, 4th "field" will be the IP
# finally pipes to sort with -u (unique) for a unique ip list!

for url in $(cat "$1")
  do host $url
done |
  grep "has address" |
  cut -d" " -f4 |
  sort -u