(open filename mode)

Open that file.

This function makes a file's filename accessible for input and output functions. The filename argument represents the path and filename of the file to open.

The open function returns a file descriptor (an 8-digit hexadecimal number) for the opened file, which should be stored as a variable using the setq function. Once you have the file descriptor, you must refer to the file using the file descriptor-not the filename!

The mode argument has three options, which must be in lowercase:

Mode	Meaning
"r"	Open the file as read-only; returns nil if the file does not exist.
"w"	Open the file for writing; overwrites existing data; creates a new file if non-existent.
"a"	Open the file for writing; append to existing data; creates a new file if non-existent.

Examples

Code	Returns
(setq n (open "existing.txt" "w"))	<File: #2190dec2>
(setq n (open "noexist.lsp" "r"))	nil
(setq n (open "\\sample\\exiting.txt" "a")	<File: #2190c2c3>

NOTES

In append mode, new data is added to the end of the existing file.
LISP only reads ASCII files (no binary files) using sequential access (no random access).
To separate subfolder names, you use either two backslashes ( \\ ) or a single forward slash ( / ).

Tell me about...

(close file-descriptor)

(read-line [file-descriptor])

(write-line string [file-descriptor])

LISP Compatibility

Programming Overview of LISP (LISt Processing) Language