redhat man page for flush

flush(n)						       Tcl Built-In Commands							  flush(n)

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NAME
       flush - Flush buffered output for a channel

SYNOPSIS
       flush channelId
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DESCRIPTION
       Flushes	any  output  that  has been buffered for channelId.  ChannelId must be a channel identifier such as returned by a previous open or
       socket command, and it must have been opened for writing.  If the channel is in blocking mode the command does not  return  until  all  the
       buffered  output  has been flushed to the channel. If the channel is in nonblocking mode, the command may return before all buffered output
       has been flushed; the remainder will be flushed in the background as fast as the underlying file or device is able to absorb it.

SEE ALSO
       file(n), open(n), socket(n)

KEYWORDS
       blocking, buffer, channel, flush, nonblocking, output

Tcl									7.5								  flush(n)