How do you escape apostrophe in single quoted string in bash?
In single quotes, no escaping is possible. There is no way how to include a single quote into single quotes. See Quoting in man bash.
In addition to POSIX-supported single- and double-quoting, bash supplies an additional type of quoting to allow a small class of escaped characters (including a single quote) in a quoted string:
$ echo $'\'Hello World\''
'Hello World'
See the QUOTING section in the bash man page, near the end of the section. (Search for "ANSI C".)