In a double-quoted string, the sequence  "\b" is a backspace control code. See following examples in double- and single-quoted strings.

perl -wMstrict -e "my $s = qq(abcdX\befg);   print $s"
abcdefg
perl -wMstrict -e "my $s = qq(abcdX \befg);  print $s"
abcdXefg
perl -wMstrict -e "my $s = q(abcdX\befg);    print $s"
abcdX\befg
perl -wMstrict -e "my $s = q(abcdX \befg);   print $s"
abcdX \befg
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See Quote and Quote like Operators in perlop.