trap: interactive bash exits on resending SIGINT twice

[Martijn Dekker]

Setting the following trap makes an interactive bash (any version) exit 
on issuing SIGINT:

trap 'trap "true" INT; kill -s INT $$; trap - INT; kill -s INT $$' INT
#     ^^^^^^^^^^^^^^^ eat signal       ^^^^^^^^^^ unset trap

After setting that trap, pressing Ctrl+C, or otherwise causing SIGINT to 
be sent, causes an interactive bash to exit.

Expected behaviour: no exit.
Confirmed on macOS and Debian.

Ignoring the signal instead of merely eating it seems to be an effective 
workaround on more recent bash versions:
trap 'trap "" INT; kill -s INT $$; trap - INT; kill -s INT $$' INT
This avoids an interactive shell exiting on SIGINT on bash 4.4 and 5.0, 
but not 4.3 or earlier.

- M.

--
modernish -- harness the shell
https://github.com/modernish/modernish