why does this single quoted string get interpreted when it's inside of a command substitution

问题

Compare these two lines of shell script:

printf '%s' 's/./\\&/g'                    #1, s/./\\&/g
printf '%s' `printf '%s' 's/./\\&/g'`      #2, s/./\&/g

My question is: why does the single-quoted double backslashes get interpreted as a single backslash for the second line of script?

回答1:

Starting from

printf '%s' `printf '%s' 's/./\\&/g'`

The expression inside backticks returns s/./\\&/g as in the first expression, without single quotes, so you get

printf '%s' s/./\\&/g

The first backslash escapes the second one, so it prints s/./\&/g.

来源：https://stackoverflow.com/questions/37788936/why-does-this-single-quoted-string-get-interpreted-when-its-inside-of-a-command