$ perl -de 1

Loading DB routines from perl5db.pl version 1.3
Editor support available.

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

main::(-e:1):   1
  DB<1> $str = '  x  '; $str =~ s/^\s+((?:.+\S)?)\s+$/$1/s;

  DB<2> x $str
0  ' x'