chore(kb): import notes from an old repository

knowledge base/shell.md

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+# Shell
+
+```shell
+$ cat /etc/locale.conf 
+LANG=en_US.UTF-8
+LC_NUMERIC=en_GB.UTF-8
+LC_TIME=en_GB.UTF-8
+LC_MONETARY=en_GB.UTF-8
+LC_PAPER=en_GB.UTF-8
+LC_MEASUREMENT=en_GB.UTF-8
+
+$ locale
+LANG=en_US.UTF-8
+LC_CTYPE="en_US.UTF-8"
+LC_NUMERIC=en_GB.UTF-8
+LC_TIME=en_GB.UTF-8
+LC_COLLATE="en_US.UTF-8"
+LC_MONETARY=en_GB.UTF-8
+LC_MESSAGES="en_US.UTF-8"
+LC_PAPER=en_GB.UTF-8
+LC_NAME="en_US.UTF-8"
+LC_ADDRESS="en_US.UTF-8"
+LC_TELEPHONE="en_US.UTF-8"
+LC_MEASUREMENT=en_GB.UTF-8
+LC_IDENTIFICATION="en_US.UTF-8"
+LC_ALL=
+```
+
+## See also
+
+- [Shellcheck]
+
+[shellcheck]: https://www.shellcheck.net/
+
+## Further readings
+
+- [How can I declare and use boolean variables in a shell script]?
+- [What does LC_ALL=C do]?
+- [Exit Codes With Special Meanings]
+- [How to check if running as root in a bash script]
+
+[exit codes with special meanings]: https://tldp.org/LDP/abs/html/exitcodes.html
+[how can i declare and use boolean variables in a shell script]: https://stackoverflow.com/questions/2953646/how-can-i-declare-and-use-boolean-variables-in-a-shell-script#21210966
+[how to check if running as root in a bash script]: https://stackoverflow.com/questions/18215973/how-to-check-if-running-as-root-in-a-bash-script#21622456
+[what does lc_all=c do]: https://unix.stackexchange.com/questions/87745/what-does-lc-all-c-do#87763