Appends lines of text to a specified file but only if the line doesn't already exist

.bash_function_append

function append(){
    count=$#;
    filename=${!count}
    for i in "$@"; do
        if ! [[ "$filename" = "$i" ]]; then
            grep -q -F "$i" $filename || echo "$i" >> $filename
        fi
    done        
}

# usage 
# $ append "line one" "line two" "line one" "line "two" filename.txt
# filename.txt
#line one
#line two