Input/Output Command Summary

The following sections describe how to open, read, and write files. The basic model is that you open a file, read or write it, then close the file. Network sockets also use the commands described here. Socket programming is discussed in Chapter 17, and more advanced event-driven I/O is described in Chapter 16. Table 9-5 lists the basic commands associated with file I/O:

Table 9-5. Tcl commands used for file access

open what ?access? ?permissions?	Returns channel ID for a file or pipeline.
puts ?-nonewline? ?channel? string	Writes a string.
gets channel ?varname?	Reads a line.
read channel ?numBytes?	Reads numBytes bytes, or all data.
read -nonewline channel	Reads all bytes and discard the last \n.
tell channel	Returns the seek offset.
seek channel offset ?origin?	Sets the seek offset. origin is one of start, current, or end.
eof channel	Queries end-of-file status.
flush channel	Writes buffers of a channel.
close channel	Closes an I/O channel.