This is from stackoverflow ( https://stackoverflow.com/questions/60166019/ ) and it looks like a bug:
$ bash --version GNU bash, version 5.0.7(3)-release (x86_64-pc-linux-gnu) Copyright (C) 2019 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software; you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. $ $ set -H $ true `# !xxx` bash: !xxx`: event not found $ true `# # !xxx` $