When I press Ctrl+T while some program is running in a terminal, I get some extra output, e.g.:

$ ping -q -c 100 google.com
PING google.com ( 56 data bytes
load: 2.39  cmd: ping 5374 running 0.00u 0.00s
2/2 packets received (100.0%) 33.914 min / 34.169 avg / 34.423 max

Where does the output come from? Are there any other useful shortcuts that can be handled by a terminal?

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    I believe this is a BSD (only?) thing. Ctrl+T requests status info from the terminal driver. – Kusalananda Oct 20 '19 at 21:02
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    Searching for Ctrl-T shows this. – Thomas Dickey Oct 20 '19 at 22:25
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    Ctrl-T goes back to at least TOPS-20 on the DESCSYSTEM-20. – Johan Myréen Oct 21 '19 at 6:32

On some Unix-style systems (BSDs and macOS), CtrlT sends SIGINFO to the running process. Some commands handle this directly; otherwise, it’s handled by the kernel, and that’s what produces the output you’re seeing.

SIGINFO on GNU Linux (Arch Linux) missing has more on the topic.

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