What is the difference between using $1 vs \1 in Perl regex substitutions?

Question

I\'m debugging some code and wondered if there is any practical difference between $1 and \\1 in Perl regex substitutions

For example:

my $package_n         


        

Answer 1

From perldoc perlre:

The bracketing construct "( ... )" creates capture buffers. To refer to the current contents of a buffer later on, within the same pattern, use \1 for the first, \2 for the second, and so on. Outside the match use "$" instead of "\".

The \ notation works in certain circumstances outside the match. But it can potentially clash with octal escapes. This happens when the backslash is followed by more than 1 digits.