我正在尝试在bash shell脚本中将grep用作变量和函数。当grep用作变量时，我得到所需的输出。将grep用作函数时，我没有得到想要的输出。

将grep用作变量的脚本如下：

#! /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

运行脚本时的输出是

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

exit code of search  mmshutdown: Finished is 0

FILE SYSTEM UnmOUNTED SUCESSFULLY

函数中用于grep的脚本如下：

#! /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

运行脚本时的输出是

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

有人可以指出这里出了什么问题吗？为什么将grep用作函数不能提供所需的输出？