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NAME
open - Open a file
SYNOPSIS
open fileName ?access? ?permissions?
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DESCRIPTION
This command opens a file and returns an identifier that may be used in future invocations of commands like read, puts, and close. FileName gives the name of the file to open; if it starts with a tilde then tilde substitution is performed as described for Tcl_TildeSubst. If the first character of fileName is ``|'' then the remaining characters of fileName are treated as a command pipeline to invoke, in the same style as for exec. In this case, the identifier returned by open may be used to write to the command's input pipe or read from its output pipe.
The access argument indicates the way in which the file (or command pipeline) is to be accessed. It may take two forms, either a string in the form that would be passed to the fopen library procedure or a list of POSIX access flags. It defaults to ``r''. In the first form access may have any of the following values:
If a file is opened for both reading and writing then seek must be invoked between a read and a write, or vice versa (this restriction does not apply to command pipelines opened with open). When fileName specifies a command pipeline and a write-only access is used, then standard output from the pipeline is directed to the current standard output unless overridden by the command. When fileName specifies a command pipeline and a read-only access is used, then standard input from the pipeline is taken from the current standard input unless overridden by the command.
KEYWORDS
access mode, append, controlling terminal, create, file, non-blocking, open, permissions, pipeline, process