Shell Programming and Scripting

#! /bin/sh                                                                      
                                                                                
echo "The current users are:"                                                   
                                                                                
who | awk '{print $1}' | sort > temp1                                           
cp temp1 temp2                                                                  
more temp1                                                                      
                                                                                
while true                                                                      
do                                                                              
    who | awk '{print $1}' | sort > temp2                                       
    cmp -s temp1 temp2                                                          
                                                                                
    case "$?" in                                                                
                                                                                
    0)                                                                          
        echo "No user has logged in/out in the last 5 seconds."                 
        ;;                                                                      
                                                                                
    1)                                                                          
        user='gayathri'                                                         
        file=`grep $user temp1 temp2 | cut -c 1-5`  
        file=`grep $user temp1 temp2 | cut -c 1-5`                              
                                                                                
        if [ $file = "temp1" ]                                                  
            echo "User "$user" has logged out."                                 
                                                                                
                                                                                
        if [ $file = "temp2" ]                                                  
            echo "User "$user" has logged in."                                  
        ;;                                                                      
                                                                                
    esac                                                                        
                                                                                
    rm temp1                                                                    
    mv temp2 temp1                                                              
                                                                                
done