#! /bin/bash
 
age=60
 
# for using And operator use &&
if [ "$age" -gt 18] && ["$age" -lt 30 ]
then
  echo "valid age"
  else
  echo "age not valid"
fi
 
#  The -a option provide
# an alternative compound condition test.
if [ "$age" -gt 18 -a "$age" -lt 30 ]
then
  echo "valid age"
  else
  echo "age not valid"
fi
 
# if [[ $condition1 && $condition2 ]]    # Also works.
if [[ "$age" -gt 18 && "$age" -lt 30 ]]
then
  echo "valid age"
  else
  echo "age not valid"
fi