Comparing send To puts
Both the send
command and the puts
command cause characters to be output. However, they have differences which should already be apparent. But I will compare and contrast them here just to make things clear. Note that all of the variations on send
follow the style of the send
command itself. For example, it is possible to call send_user
with the -h
flag or send_log
with the --
flag.
The primary difference between send
and puts
is that send
works with processes started by spawn
, whereas puts
works with files opened by Tcl’s open
command. For example, to write an AT
-style reset command (the characters "ATZ\r
“) to a modem with a serial interface, puts
could be used as follows:
set file [open "/dev/modem" "w"] puts -nonewline $file "ATZ\r"
Doing the same thing with send
requires a spawned process instead of an open file.
spawn tip modem send −i $spawn_id "ATZ\r"
In this example, the "−i $spawn_id
" is not needed. It is just here to contrast it with the $file
argument in the puts
. Without the −i
specification, send
writes to the tip
process anyway because spawn
automatically sets spawn_id
. In contrast, with no file specification, puts
writes to the standard output. The previous open
has no effect on the default destination of puts
.
puts "ATZ\r" ;# write to standard output send "ATZ\r" ;# write to currently spawned process
In UNIX, processes can be viewed as files (to a degree). The puts
command, thus, can write to processes as well—but only those opened by open
. The ...
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