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### 2.6 Files

Files can only be created using the built-in function `open`. Files are either readable or writeable. If a file is writeable, text written to the file may optionally be appended to any existing text.

    "a" "r" ! open = f1;
    "b" "w" ! open = f2;
    "c" "a" ! open = f3;

    # Read one character
    f1 ! read | stdout temp ! write;
    # Write a string
    f2 "Aaar" ! write;
    # Append a string
    f3 "Ouu" ! write;

    f1!close;f2!close;f3!close;

To read an entire file, one must use a loop construct. See Loops. When there are no more characters left, the `read` function returns an empty string. Using equality testing, reading a complete file is thus possible. See Conditionals.

    filename "r" ! open = f;
    {f ! read = c; stdout c ! write; c "" ! equal ! not = return;} ! loop;

At this point, it may not be obvious why this works. This will be explained in the next sections.