여기서 getopts나 grep에 어떤 문제가 있나요?

    #!/bin/bash

    #return codes:
    STATE_OK=0
    STATE_WARNING=1
    STATE_CRITICAL=2
    STATE_UNKNOWN=3

    if [ $# -lt 4 ]
    then
       echo "UNKNOWN: Please, Pass Enough Parameters"
       exit $STATE_UNKNOWN
    fi

    while getopts ":w:c:f:p" opt
    do
     case ${opt} in
       w )
         WARN=${OPTARG}
         ;;
       c )
         CRIT=${OPTARG}
         ;;
       f )
         FILE=${OPTARG}
         ;;
       p )
         PATTERN=${OPTARG}
         ;;
     esac
    done

    COUNT=$(tail -50 ${FILE} | grep -c '${PATTERN}')


    if [ $? -eq 0 ]
    then
            if [ ${COUNT} -gt ${CRIT} ]
            then
                            echo "CRITICAL: The FAIL count is now ${COUNT}"
                            echo $STATE_CRITICAL

            elif [ ${COUNT} -le ${CRIT} -a ${COUNT} -ge ${WARN} ]
                    then
                            echo "WARNING: The FAIL count is now ${COUNT}"
                            echo $STATE_WARNING
            else
                            echo "OK: The FAIL count is now ${COUNT}"
                            echo $STATE_OK
            fi

    else

            echo "CRITICAL: Error while getting the data"
            echo $STATE_CRITICAL
    fi