$ perl -le " print sort { warn $f=$a <=> $b; $f } 1,2,3,4,5
-1 at -e line 1.
-1 at -e line 1.
-1 at -e line 1.
1 at -e line 1.
-1 at -e line 1.
1 at -e line 1.
1 at -e line 1.
1 at -e line 1.
12345

$ perl -le " print sort { warn $f=$a <=> $b; $f } 5,4,3,2,1
1 at -e line 1.
1 at -e line 1.
1 at -e line 1.
1 at -e line 1.
1 at -e line 1.
12345

$ perl -le " print sort { warn $f=$a <=> $b; $f } 1,4,2,3,5
-1 at -e line 1.
-1 at -e line 1.
-1 at -e line 1.
-1 at -e line 1.
1 at -e line 1.
-1 at -e line 1.
1 at -e line 1.
1 at -e line 1.
1 at -e line 1.
12345

$ perl -le " @f; print sort { $f=$a <=> $b; printf qq{%3s == %3s <=> %3s\n}, $f,$a,$b; push @f,$f; $f } 1 .. 11; print int @f; print  qq{@f}; "
 -1 ==   1 <=>   2
 -1 ==   3 <=>   4
 -1 ==   5 <=>   6
 -1 ==   7 <=>   8
 -1 ==   9 <=>  10
 -1 ==   1 <=>   3
  1 ==   3 <=>   2
 -1 ==   1 <=>   5
  1 ==   5 <=>   2
  1 ==   5 <=>   3
  1 ==   5 <=>   4
 -1 ==   7 <=>   9
  1 ==   9 <=>   8
 -1 ==   7 <=>  11
  1 ==  11 <=>   8
  1 ==  11 <=>   9
  1 ==  11 <=>  10
 -1 ==   1 <=>   7
  1 ==   7 <=>   2
  1 ==   7 <=>   3
  1 ==   7 <=>   4
  1 ==   7 <=>   5
  1 ==   7 <=>   6
1234567891011
23
-1 -1 -1 -1 -1 -1 1 -1 1 1 1 -1 1 -1 1 1 1 -1 1 1 1 1 1