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tell(1t) [opensolaris man page]

tell(1T)						       Tcl Built-In Commands							  tell(1T)

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NAME
tell - Return current access position for an open channel SYNOPSIS
tell channelId _________________________________________________________________ DESCRIPTION
Returns an integer string giving the current access position in channelId. This value returned is a byte offset that can be passed to seek | in order to set the channel to a particular position. Note that this value is in terms of bytes, not characters like read. The value returned is -1 for channels that do not support seeking. 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. EXAMPLE
Read a line from a file channel only if it starts with foobar: # Save the offset in case we need to undo the read... set offset [tell $chan] if {[read $chan 6] eq "foobar"} { gets $chan line } else { set line {} # Undo the read... seek $chan $offset } SEE ALSO
file(1T), open(1T), close(1T), gets(1T), seek(1T), Tcl_StandardChannels(3TCL) KEYWORDS
access position, channel, seeking ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +--------------------+-----------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +--------------------+-----------------+ |Availability | SUNWTcl | +--------------------+-----------------+ |Interface Stability | Uncommitted | +--------------------+-----------------+ NOTES
Source for Tcl is available on http://opensolaris.org. Tcl 8.1 tell(1T)

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seek(n) 						       Tcl Built-In Commands							   seek(n)

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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 back- wards 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(n), open(n), close(n), gets(n), tell(n), Tcl_StandardChannels(3) KEYWORDS
access position, file, seek Tcl 8.1 seek(n)
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