After thinking about recent comments about reading CSV files, and trying a few experiments,
I noticed odd behavior when using gets in nonblocking mode on files that did not end with a newline.

The first [gets] attempting to read the last text before the end of file returned no data,
(returned -1 if a variable name was supplied) and the file was fblocked after the read attempt.
A second [gets] returned the text up to the end of file, cleared fblocked and set EOF.
Any subsequent gets returned no data (returned -1 if a variable was given) and EOF remained set.

This behavior does not appear to be explained on the gets or fconfigure man pages. Where is this documented?

transcripts from tkcon:

# create a short file with no trailing newline
(try) 57 % set ff [open no-eol.txt w]
file6
(try) 58 % puts -nonewline $ff "asdf"
(try) 59 % close $ff
(try) 60 % file size no-eol.txt
4

# gets in nonblocking mode
(try) 70 % set ff [open no-eol.txt r]
file6
(try) 71 % fconfigure $ff -blocking 0
(try) 72 % fblocked $ff
0 (try) 73 % gets $ff line
-1
# no new line after current file location, fblocked waiting for a newline to appear?
(try) 74 % fblocked $ff
1 (try) 75 % eof $ff
0 # at this point no EOF, but fblocked is true, issue another gets
(try) 76 % gets $ff line
4 # line is read up to to end of file!
(try) 77 % set line
asdf
(try) 78 % eof $ff
1 (try) 79 % fblocked $ff
0 # now at this point have EOF, nothing left to read
(try) 80 % gets $ff line
-1
(try) 81 % fblocked $ff
0 (try) 82 % eof $ff
1 # the file I/O configuration was
(try) 85 % fconfigure $ff
-blocking 0 -buffering full -buffersize 4096 -encoding utf-8 -eofchar {} -translation auto

Dave B

Am 06.11.22 um 04:59 schrieb clt.to.davebr@dfgh.net:
> After thinking about recent comments about reading CSV files, and trying a few experiments,
> I noticed odd behavior when using gets in nonblocking mode on files that did not end with a newline.

non-blocking mode doesn't make much sense on a file. On a socket or
command pipe, non-blocking is useful because if the sender decides not
to send any data, you would otherwise wait infinitely long. A file is
always ready. My guess is that you actually want to do something else.

Christian