You could initialise your variables using the \x?? hexadecimal character values to avoid confusion.

$ perl -E '
say for (
   qq{a\x5cb},
   qq{a\x5c\x5cb},
   qq{a\x5c\x5c\x5cb},
   qq{a\x5c\x5c\x5c\x5cb},
   );'
a\b
a\\b
a\\\b
a\\\\b
$
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I hope this is helpful.

Update: Another way would be to use chr.

$ perl -E '
> @arr = map { q{A} . do { chr 0x5c } x $_ . q{B} } 1 .. 4;
> say for @arr;'
A\B
A\\B
A\\\B
A\\\\B
$
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