1tell(n)                      Tcl Built-In Commands                     tell(n)
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NAME

8       tell - Return current access position for an open channel
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SYNOPSIS

11       tell channelId
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DESCRIPTION

16       Returns  an  integer string giving the current access position in chan‐ │
17       nelId.  This value returned is a byte offset that can be passed to seek │
18       in  order  to set the channel to a particular position.  Note that this │
19       value is in terms of  bytes,  not  characters  like  read.   The  value
20       returned is -1 for channels that do not support seeking.
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22       ChannelId must be an identifier for an open channel such as a Tcl stan‐ │
23       dard channel (stdin, stdout, or stderr), the return value from an invo‐ │
24       cation  of  open or socket, or the result of a channel creation command │
25       provided by a Tcl extension.
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EXAMPLE

28       Read a line from a file channel only if it starts with foobar:
29              # Save the offset in case we need to undo the read...
30              set offset [tell $chan]
31              if {[read $chan 6] eq "foobar"} {
32                  gets $chan line
33              } else {
34                  set line {}
35                  # Undo the read...
36                  seek $chan $offset
37              }
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SEE ALSO

41       file(n), open(n), close(n), gets(n), seek(n), Tcl_StandardChannels(3)
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KEYWORDS

45       access position, channel, seeking
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49Tcl                                   8.1                              tell(n)
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