原创 TCL Open 命令

open fileName

open fileName access

Description

This command opens a file, serial port, or command pipeline and returns a channel identifier that may be used in future invocations of commands like read, puts, and close. If the first character of fileName is not | then the command opens a file: fileName gives the name of the file to open, and it must conform to the conventions described in the filename manual entry.

The access argument, if present, indicates the way in which the file (or command pipeline) is to be accessed. In the first form access may have any of the following values:

r

Open the file for reading only; the file must already exist. This is the default value if access is not specified.

r+

Open the file for both reading and writing; the file must already exist.

w

Open the file for writing only. Truncate it if it exists. If it does not exist, create a new file.

w+

Open the file for reading and writing. Truncate it if it exists. If it does not exist, create a new file.

a

Open the file for writing only. If the file does not exist, create a new empty file. Set the file pointer to the end of the file prior to each write.

a+

Open the file for reading and writing. If the file does not exist, create a new empty file. Set the initial access position to the end of the file.

All of the legal access values above may have the character b added as the second or third character in the value to indicate that the opened channel should be configured with the -translation binary option, making the channel suitable for reading or writing of binary data.

In the second form, access consists of a list of any of the following flags, all of which have the standard POSIX meanings. One of the flags must be either RDONLY, WRONLY or RDWR.