I'm just going to leave this here in case someone else finds themselves in this rabbit hole. Bash can break pipes with the debug trap. I circled around it but didn't find a fix other than "don't run external programs in the debug trap"
Bash has a few special trap handlers just for the shell. One is "debug" which executes at various points. You can see it like so:
trap 'echo trap' debugwhere it can print things to the shell before commands are executed.
It appears to me that if the trap handler calls any external program--even if there is no output--then pipes are blocked at 64k. In the example above, echo is a bash built-in and seems to not cause this behavior. So let's use the system /bin/echo to trigger the bug:
$ trap '/bin/echo trap' debug
$ jot -b '' 65537 | wc -l
trap
trap... hangs. If you hit Ctrl-C you'll see that wc got 64k of the output but blocked on that last byte.
^C
65536
trapI got bit by this because I was calling tput sgr0 in the debug trap. The work around is to capture what tput outputs in a bash variable outside of the trap handler, then inside the trap handler use the builtin printf to send to the console.
Looked at a few things with dtruss and the system source to rule out an ioctl call, but nothing obvious jumps out as the explanation. Let me know if you figure it out!
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