Tcl Built-In Commands                                    seek(1T)





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  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  channel
     before  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 error
     occurs 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                        1






Tcl 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),
     TclStandardChannels(3TCL)


KEYWORDS
     access position, file, seek

ATRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:

     
       ATRIBUTE TYPE     ATRIBUTE VALUE
    
     Availability         SUNWTcl        
    
     Interface Stability  Uncommitted    
    

NOTES
     Source for Tcl is available on http:/opensolaris.org.














Tcl                     Last change: 8.1                        2