# Prints the lines of a file '$2' which contain the text '$1'.
grepper () {
    if [ -f "$2" ] ; then
        custom_input=$(cat "$2")
    else
            custom_input="$($2)"
    fi
    printf "$custom_input\n" | while IFS= read -r grepper_line
    do
        case "$grepper_line" in
        *"$1"*)
            printf '%s\n' "$grepper_line"
            ;;
    esac
    done
    return 0
}

grepper "$1" "$2"