why does grep works when used as a variable and does not when used as a function in linux shell script?

I am trying to use grep as a variable and a function in a bash shell script. I get the desired output when grep is used as an variable. I do not get the desired output when grep is used as an function.

The script used for grep as a variable is as below:

#! /bin/bash

grep=$(grep -ico "mmshutdown: Finished" mmshutdown-output.txt)
#grep()
#{
#        grep -ico "mmshutdown: Finished" mmshutdown-output.txt
#}
status()
{
        echo $?
}

if [[ "grep" -gt "0" ]];
then
        echo
        echo "exit code of search  mmshutdown: Finished is $(status)"
        echo
        echo "FILE SYSTEM UNMOUNTED SUCESSFULLY"
        sleep 3
else
        echo "exit code of search mmshutdown: Finished is $(status)"
        echo "check output log file mmshutdown.txt"
        sleep 3
fi

the out put when we run the script is

[root@ad ~]# ./grep-variable.sh

exit code of search  mmshutdown: Finished is 0

FILE SYSTEM UNMOUNTED SUCESSFULLY

The script used for grep in function is as below:

#! /bin/bash

#grep=$(grep -ico "mmshutdown: Finished" mmshutdown-output.txt)
grep()
{
        grep -ico "mmshutdown: Finished" mmshutdown-output.txt
}
status()
{
        echo $?
}


if [[ "grep" -gt "0" ]];
then
        echo
        echo "exit code of search  mmshutdown: Finished is $(status)"
        echo
        echo "FILE SYSTEM UNMOUNTED SUCESSFULLY"
        sleep 3
else
        echo "exit code of search mmshutdown: Finished is $(status)"
        echo "check output log file mmshutdown.txt"
        sleep 3
fi

the out put when we run the script is

[root@ad ~]# ./grep-function.sh
exit code of search mmshutdown: Finished is 1
check output log file mmshutdown.txt

Could someone point out what has gone wrong here? Why is grep when used as function not providing desired output?

Answer

Your both programs are comparing “grep” with “0” not the output of the grep command. Also -c option returns the number of lines matched.

Check the following code it works with grep as function. But as grep is as a function you will need to call original grep i.e. command with complete path else it will go in an infinite loop. Send output to /dev/null and process on command execution status.

#! /bin/bash
set -x
#grep=$(grep -ico "mmshutdown: Finished" mmshutdown-output.txt)
grep()
{
        return $(/bin/grep -ico "mmshutdown: Finished" mmshutdown-output.txt > /dev/null)
}
status()
{
        echo $?
}


if  grep;
then
        echo
        echo "exit code of search  mmshutdown: Finished is $(status)"
        echo
        echo "FILE SYSTEM UNMOUNTED SUCESSFULLY"
        sleep 3
else
        echo "exit code of search mmshutdown: Finished is $(status)"
        echo "check output log file mmshutdown.txt"
        sleep 3
fi