Shell Programming and Scripting

hostname="network"
ip="192.168.1.1"
netmask=""

variables=( $hostname $ip $netmask  )

for var in ${variables[@]}
do

      if [ "$var" == "" ]; then
                $var="--"
       fi
done

echo hostname: $hostname
echo ip: $ip
echo netmask: $netmask

mTst=$(echo ${mTst} | sed 's/^$/--/')

for var in ${variables[@]} 
do       
$var=$(echo ${var} | sed 's/^$/ --/') 
done

# if the variable has been set but is now "empty"
if [ -z "$var" ] ; then
  # do something
fi
# or parameter substitution, when the variable is not set
${var:-"default value for var"}

#!/bin/bash

hostname="network"
ip="192.168.1.1"
netmask=""

variables=( $hostname $ip $netmask  )

echo hostname: ${variables[0]:=--}
echo ip: ${variables[1]:=--}
echo netmask: ${variables[2]:=--}

exit 0

#!/bin/sh

hostname="network"
ip="192.168.1.1"
netmask=""

echo hostname: ${hostname:=--}
echo ip: ${ip:=--}
echo netmask: ${netmask:=--}

exit 0

hostname=$(echo ${hostname} | sed 's/^$/--/')
ip=$(echo ${ip} | sed 's/^$/--/')
netmask=$(echo ${netmask} | sed 's/^$/--/')

echo "hostname: $hostname"
echo "ip: $ip"
echo "netmask: $netmask"