Question

How can i comapre the CPU usage value using shell script, i get a error as [: =: unary operator expected at the line if [ $message -ne "" ]

   #!/bin/sh

    expected_cpuusage="95"
    cpu_usage=`top -n 1 -b|grep Cpu|awk '{print $2}'|cut -d"%" -f1""`
    message=""
    if [ $cpu_usage -gt $expected_cpuusage ]    ##{x%?}
    then
       echo "CPU usage exceeded";
       if [ $message -ne "" ]
       then
         message="$message\n\nCPU usage exceeded configured usage limit \nCurrent CPU usage is $cpu_usage\nConfigured CPU usage is $expected_cpuusage";
       else
         message="CPU usage exceeded configured usage limit \nCurrent CPU usage is $cpu_usage\nConfigured CPU usage is $expected_cpuusage";
       fi ;
    fi

Answer 1

> is a redirection operator. You want -gt

if [ $cpu_usage -gt $expected_cpuusage ]

This requires that $cpu_usage look like an integer and will fail and generate an error if it does not. (ie, if it contains characters other than 0-9. -gt does not compare floating point values, so strings that contain ‘.’ will not work.) For floating point comparisons, use expr:

if expr $cpu_usage \> $expected_cpuusage > /dev/null; then 

There are slicker ways to do this comparison using bash builtins like [[, but these constructs limit the portability of the script.
The other error you are seeing occurs when you use an empty string. Try using quotes:

if [ "$message" -ne "" ]

but it is much clearer to use:

if [ -n "$message" ]