s/^(.)(.)(.*)/$2$1$3/s;           # 12345 -> 21345
s/^(.)(.)(.)(.*)/$1$3$2$4/s;      # 12345 -> 13245
s/^(..)(.)(.)(.*)/$1$3$2$4/s;     # 12345 -> 12435
s/^(...)(.)(.)(.*)/$1$3$2$4/s;    # 12345 -> 12354

##</code><code>##

s/^()(.)(.)(.*)/$1$3$2$4/s;

##</code><code>##

my $dots = "..";
s/^($dots)(.)(.)(.*)/$1$3$2$4/s;     # 12345 -> 12435

##</code><code>##

my $str = "12345";
my $dots = "";
while (length($dots) <= length($str)-2) {
   $_ = $str;
   s/^($dots)(.)(.)(.*)/$1$3$2$4/s;
   print;
   $dots .= ".";
}