Provided by: tcl8.5-doc_8.5.19-4_all 
NAME
seek - Change the access position for an open channel
SYNOPSIS
seek channelId offset ?origin? ________________________________________________________________________________________________________________
DESCRIPTION
Changes the current access position for channelId.
ChannelId must be an identifier for an open channel such as a Tcl standard channel (stdin, stdout, or
stderr), the return value from an invocation of open or socket, or the result of a channel creation
command provided by a Tcl extension.
The offset and origin arguments specify the position at which the next read or write will occur for
channelId. Offset must be an integer (which may be negative) and origin must be one of the following:
start The new access position will be offset bytes from the start of the underlying file or device.
current The new access position will be offset bytes from the current access position; a negative
offset moves the access position backwards in the underlying file or device.
end The new access position will be offset bytes from the end of the file or device. A negative
offset places the access position before the end of file, and a positive offset places the
access position after the end of file.
The origin argument defaults to start.
The command flushes all buffered output for the channel before the command returns, even if the channel
is in nonblocking mode. It also discards any buffered and unread input. This command returns an empty
string. An error occurs if this command is applied to channels whose underlying file or device does not
support seeking.
Note that offset values are byte offsets, not character offsets. Both seek and tell operate in terms of
bytes, not characters, unlike read.
EXAMPLES
Read a file twice:
set f [open file.txt]
set data1 [read $f]
seek $f 0
set data2 [read $f]
close $f
# $data1 == $data2 if the file wasn't updated
Read the last 10 bytes from a file:
set f [open file.data]
# This is guaranteed to work with binary data but
# may fail with other encodings...
fconfigure $f -translation binary
seek $f -10 end
set data [read $f 10]
close $f
SEE ALSO
file(3tcl), open(3tcl), close(3tcl), gets(3tcl), tell(3tcl), Tcl_StandardChannels(3tcl)
KEYWORDS
access position, file, seek