script.sh fileA fileB fileC

rm $3
while IFS="" read -r inputline; do

fgrep -q ""$inputline"" $1
if [ 1 -eq $? ]; then
    echo ""$inputline"" >>$3
fi
done <$2

#!/usr/bin/bash
rm "$3"
while IFS="" read -r inputline
do
    grep -Fq "$inputline" "$1" && echo "$inputline" >> "$3"
done < "$2"