Tcl Built-In Commands seek(1T)
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NAME
seek - Change the access position for an open channel
SYNOPSIS
seek channelId offset ?origin?
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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 offsetmoves the access position backwards in the under-
lying 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 channelbefore the command returns, even if the channel is in non-
blocking mode. It also discards any buffered and unread input. This command returns an empty string. An erroroccurs if this command is applied to channels whose underly-
ing 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. Tcl Last change: 8.1 1Tcl Built-In Commands seek(1T)
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(1T), open(1T), close(1T), gets(1T), tell(1T),Tcl_StandardChannels(3TCL)
KEYWORDSaccess position, file, seek
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:_______________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE|
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| Availability | runtime/tcl-8 |
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| Interface Stability| Uncommitted ||____________________|_________________|
NOTES Source for Tcl is available on http://opensolaris.org. Tcl Last change: 8.1 2