$ perl -de 42 foo\\n

Loading DB routines from perl5db.pl version 1.33
Editor support available.

Enter h or `h h' for help, or `man perldebug' for more help.

main::(-e:1):   42
  DB<1> $c = shift;

  DB<2> x $c
0  'foo\\n'
  DB<3> $c =~ s|\\n|\n|;

  DB<4> x $c
0  'foo
'
  DB<5>