Just like the shell interprets "\"+newline as a single newline, so does Perl in double-quoted and backtick literals.

$ perl -le'$_="\
"; print length;'
1
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To pass "\"+newline to the shell, you'll need to escape the backslash.

$ perl -e'print
   `echo foo
   bar`
'
sh: line 1: bar: command not found
foo

$ perl -e'print
   `echo foo \
   bar`
'
sh: line 1: bar: command not found
foo

$ perl -e'print
   `echo foo \\
   bar`
'
foo bar
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