seek(n) - phpMan

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?
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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  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 posi-
                 tive 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 chan-
       nels whose underlying file or device does not support seeking.

       Note that offset values are byte offsets, not character offsets.  Both seek and tell oper-
       ate 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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