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Member "SAOImageDS9/tcl8.6/doc/tell.n" (13 Nov 2019, 1588 Bytes) of package /linux/misc/ds9.8.1.tar.gz:


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tell

NAME
SYNOPSIS
DESCRIPTION
EXAMPLE
SEE ALSO
KEYWORDS

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(n), open(n), close(n), gets(n), seek(n), Tcl_StandardChannels(3)

KEYWORDS

access position, channel, seeking