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open (AutoLISP)

Opens a file for access by the AutoLISP I/O functions

Supported Platforms: Windows, Mac OS, and Web

Signature

(open filename mode [encoding])
filename

Type: String

Name and extension of the file to be opened. If you do not specify the full path name of the file, open assumes you are referring to the AutoCAD default drawing directory.

mode

Type: String

Indicates whether the file is open for reading, writing, or appending. Specify a string containing one of the following letters:

r Open for reading.

w Open for writing. If filename does not exist, a new file is created and opened. If filename already exists, its existing data is overwritten. Data passed to an open file is not actually written until the file is closed with the close function.

a Open for appending. If filename does not exist, a new file is created and opened. If filename already exists, it is opened and the pointer is positioned at the end of the existing data, so new data you write to the file is appended to the existing data.

The mode argument can be uppercase or lowercase.

Note: Prior to AutoCAD 2000, mode had to be specified in lowercase.
encoding

Type: String

Indicates the character encoding to use when reading the file. When a value isn't provided for the argument, the file is assumed to contain multibyte character set (MBCS) which is the legacy behavior.

Use one of the following values to specify a different character encoding:

utf8 UTF-8

utf8-bom UTF-8 with Byte Order Marks

Return Values

Type: File or nil

If successful, open returns a file descriptor that can be used by the other I/O functions. If mode "r" is specified and filename does not exist, open returns nil.

Release Information

    Releases:

  • AutoCAD R12 and later on Windows
  • AutoCAD 2011 and later on Mac OS

History

    AutoCAD 2021

  • filename argument previously accepted an ASCII text string, but now accepts a Unicode text string.
  • encoding argument is newly added.
  • LISPSYS system variable controls which AutoLISP engine is used and the behavior of the function.
    • 0 - ASCII character support and no encoding argument (legacy behavior)
    • 1 or 2 - Unicode character support
    Note: After the value of the LISPSYS system variable has been changed, AutoCAD must be restarted for the change to take affect.

    AutoCAD 2000

  • mode argument previously only accepted a lowercase value.

Examples

Windows

Open an existing file: 

(setq a (open "c:/datafiles/filelist.txt" "r"))
#<file "c:/datafiles/filelist.txt">

The following examples issue open against files that do not exist: 

(setq f (open "c:\\my documents\\new.tst" "w"))
#<file "c:\\my documents\\new.tst">

(setq f (open "nosuch.fil" "r"))
nil

(setq f (open "logfile" "a"))
#<file "logfile">
Mac OS and Web

Open an existing file: 

(setq a (open "/datafiles/filelist.txt" "r"))
#<file "/datafiles/filelist.txt">

The following examples issue open against files that do not exist: 

(setq f (open "/my documents/new.tst" "w"))
#<file "/my documents/new.tst">

(setq f (open "nosuch.fil" "r"))
nil

(setq f (open "logfile" "a"))
#<file "logfile">

Related Concepts

Related Reference

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