FileOpen() [AHK_L 42+]

Opens a file to read specific content from it and/or to write new content into it.

file := FileOpen(Filename, Flags , Encoding)



The path of the file to open, which is assumed to be in A_WorkingDir if an absolute path isn't specified.

[v1.1.17+]: Specify an asterisk (or two) as shown below to open the standard input/output/error stream:

FileOpen("*", "r")   ; for stdin
FileOpen("*", "w")   ; for stdout
FileOpen("**", "w")  ; for stderr

Either [in AHK_L 54+] a string of characters indicating the desired access mode followed by other options (with optional spaces or tabs in between); or [in AHK_L 42+] a combination (sum) of numeric flags. Supported values are described in the tables below.


The code page to use for text I/O if the file does not contain a UTF-8 or UTF-16 byte order mark, or if the h (handle) flag is used. If omitted, the current value of A_FileEncoding is used.


Access modes (mutually-exclusive)

Flag Dec Hex Description
r 0 0x0 Read: Fails if the file doesn't exist.
w 1 0x1 Write: Creates a new file, overwriting any existing file.
a 2 0x2 Append: Creates a new file if the file didn't exist, otherwise moves the file pointer to the end of the file.
rw 3 0x3 Read/Write: Creates a new file if the file didn't exist.
h     Indicates that Filename is a file handle to wrap in an object. Sharing mode flags are ignored and the file or stream represented by the handle is not checked for a byte order mark. The file handle is not closed automatically when the file object is destroyed and calling Close has no effect. Note that Seek, Tell and Length should not be used if Filename is a handle to a nonseeking device such as a pipe or a communications device.

Sharing mode flags

Flag Dec Hex Description
-rwd     Locks the file for read, write and/or delete access. Any combination of r, w and d may be used. Specifying - is the same as specifying -rwd. If omitted entirely, the default is to share all access.
  0 0x0 If Flags is numeric, the absence of sharing mode flags causes the file to be locked.
  256 0x100 Shares read access.
  512 0x200 Shares write access.
  1024 0x400 Shares delete access.

End of line (EOL) options

Flag Dec Hex Description
`n 4 0x4 Replace `r`n with `n when reading and `n with `r`n when writing.
`r 8 0x8 Replace standalone `r with `n when reading.

Return Value

If the file is opened successfully, the return value is a File object.

If the function fails, the return value is 0 and [in AHK_L 54+] A_LastError contains an error code.

Use if file or IsObject(file) to check if the function succeeded.


When a UTF-8 or UTF-16 file is created, a byte order mark is written to the file unless Encoding (or A_FileEncoding if Encoding is omitted) contains UTF-8-RAW or UTF-16-RAW.

When a file containing a UTF-8 or UTF-16 byte order mark (BOM) is opened with read access, the BOM is excluded from the output by positioning the file pointer after it. Therefore, File.Position may report 3 or 2 immediately after opening the file.

FileEncoding, File Object, FileRead


Writes some text to a file then reads it back into memory (it provides the same functionality as this DllCall example).

FileSelectFile, FileName, S16,, Create a new file:
if (FileName = "")
file := FileOpen(FileName, "w")
if !IsObject(file)
    MsgBox Can't open "%FileName%" for writing.
TestString := "This is a test string.`r`n"  ; When writing a file this way, use `r`n rather than `n to start a new line.

; Now that the file was written, read its contents back into memory.
file := FileOpen(FileName, "r-d") ; read the file ("r"), share all access except for delete ("-d")
if !IsObject(file)
    MsgBox Can't open "%FileName%" for reading.
CharsToRead := StrLen(TestString)
TestString := file.Read(CharsToRead)
MsgBox The following string was read from the file: %TestString%

Opens the script in read-only mode and read its first line.

file := FileOpen(A_ScriptFullPath, "r")
MsgBox % file.ReadLine()

Demonstrates the usage of the standard input/output streams.

; Open a console window for this demonstration:
; Open the application's stdin/stdout streams in newline-translated mode.
stdin  := FileOpen("*", "r `n")  ; Requires [v1.1.17+]
stdout := FileOpen("*", "w `n")
; For older versions:
;   stdin  := FileOpen(DllCall("GetStdHandle", "int", -10, "ptr"), "h `n")
;   stdout := FileOpen(DllCall("GetStdHandle", "int", -11, "ptr"), "h `n")
stdout.Write("Enter your query.`n\> ")
stdout.Read(0) ; Flush the write buffer.
query := RTrim(stdin.ReadLine(), "`n")
stdout.WriteLine("Your query was '" query "'. Have a nice day.")
stdout.Read(0) ; Flush the write buffer.
Sleep 5000