cat file if file content has changed from last run

ifdiff.sh

#!/usr/bin/env bash

help_string="cat or diff file if content has changed from last run"

FILE=$1
ME=$(basename $0)

if [ -z "$FILE" ]; then
    echo "USAGE: $ME <resultfile.txt>"
    echo "EXAMPLE: ifdiff.sh /tmp/changing-file.txt         - cat file when it was changed from previous run"
    echo "         ifdiff.sh /tmp/changing-file.txt diff    - show what changed from previous run"
    echo "exit with status 2 if there is no change on file since last run"
    echo ""
    exit 1
fi

FILE=$(readlink -f $FILE)

if [ ! -f "$FILE" ]; then
    exit 1
fi

OFILE="$FILE".OLD

if [ ! -f "$OFILE" ]; then
    cat $FILE
    cp $FILE $OFILE
else

    if cmp -s "$FILE" "$OFILE" ; then
        exit 2
    else
        ### WHEN SECOND ARGUMENT IS PROVIDED SHOW DIFF OTHERWISE CAT
        if [ -z $2 ]; then
            cat $FILE
        else
            diff $FILE $OFILE
        fi
        cp $FILE $OFILE
        exit 0
    fi
fi