Here is the example
$> echo "\\\`u"
\`u <<<<<<<<<<< One quote back out of three. Before the “u” is a backqupte
Differently than:
$> echo "\\\u"
\\u <<<<<<<<<<< Two quotes back out of three.
Same as for $ dollar sign
$> u=pppp
$> echo "\\\$u"
\$u
$> echo "\\\pu"
\\pu <<<<<< It returned two backslashes.
$> echo "\\$u"
\pppp
Wed 26 Nov 2025 10:54:06 AM PST
Outside doublequotes it behave as expected
$> echo $u
pppp
$> echo \\\$u
\$u
Wed 26 Nov 2025 11:04:21 AM PST
S> echo \\\pu
\pu <<<<<<<<<<<< One backslash back only
$> echo "\\\pu"
\\pu <<<<<<<<<<< Two backslashes here.
Within double-quotes the shell only dequotes the quoted special characters
$ introduces an expression
` old style command substitution
" ending double-quote
\ the escape(quote) character
So only the following are dequoted:
\$ becomes a dollar
\` becomes a backtick
\" becomes a double-quote
\\ becomes a backslash
A \u is not dequoted because the u is not special.
As a consequence
echo "\\\u"
echo "\\\\u"
have the same result. The first line dequotes one quoted backslash and leaves the following backslash.
The second line dequotes two quoted backslashes.
This was about text inside double-quotes.
Outside the rules are a bit different.
Copy that. TY