In Perl, we use $1 instead of \1 in the substitution string. The right hand side is just another interpolated string.

From perlop:

It is at this step that "\1" is begrudgingly converted to $1 in the replacement text of "s///" to correct the incorrigible sed hackers who haven't picked up the saner idiom yet. A warning is emitted if the "use warnings" pragma or the -w command-line flag (that is, the $^W variable) was set.

From Jeffrey E. F. Friedl's great book Mastering Regular Expressions:

The Perl manpage makes a concerted effort to point out that \1 is not available as a backreerence outside of a regex. (Use the variable $1 instead.) \1 is much more than a simple notational convenience - the variable $1 refers to a string of static text matched during some previously completed successful match. On the other hand, \1 is a true regex metacharacter to match text similar to that matched within the first parenthesized subexpression (...)

perl -we's//\1/' 2>&1 |splain

\1 better written as $1 at -e line 1 (#1)
(W syntax) Outside of patterns, backreferences live on as variables. The use of backslashes is grandfathered on the right-hand side of a substitution, but stylistically it's better to use the variable form because other Perl programmers will expect it, and it works better if there are more than 9 backreferences.

And dot star (.*) is bad in this case.

2;0 juerd@ouranos:~$ perl -e'undef christmas'
Segmentation fault
2;139 juerd@ouranos:~$
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