Tcl/Tk in a Nutshell

Name

open

open fileName [access] [permissions]

Open the specified file, device, or command pipeline using an access specifier (described in the following list). Return a channel identifier that can be used in subsequent I/O commands. FileName can be a string corresponding to a regular file. If the first character is “|”, open a command pipeline (can be open for read or write). FileName can also be a device name for a serial port (platform dependent). When creating a new file, optionally specify the access permissions to be given to the file in conjunction with the process’s file creation mask (default is read and write access for all).

Access specifiers:

r	Open for reading; file must already exist (default).
r+	Open for read and write; file must already exist.
w	Open for write; create new file if needed.
w+	Open for read and write; create new file if needed.
a	Open existing file for write, appending to end.
a+	Open for read and write, appending to end.

Alternate (POSIX) form for access (must specify one of the first three):

RDONLY	Open for reading.
WRONLY	Open for writing.
RDWR	Open for read and write.

You can add one or more of the following (as a list):

APPEND	Open file for append.
CREAT	Create file if it does not exist.
EXCL	Report error if file does already exist.
NOCTTY	For terminals, do not become controlling terminal for process.
NONBLOCK	Open in nonblocking mode.
TRUNC	Truncate file to zero length.