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http://blog.sina.com.cn/s/blog_4af3f0d20100etxj.html

sort <=> and cmp

Perl has two operators <=> and cmp,

which are very useful when wishing to sort arrays. $a <=> $b returns -1 if $a is numerically lesser than $b, 1 if it's greater, and zero if they are equal.

cmp does the same for string comparison. For instance the previous example could be re-written as:

[liuguiyou@localhost perl]$ cat sort.pl
  #!/usr/bin/perl
use strict;
  use warnings;
my @array = (100,5,8,92,-7,34,29,58,8,10,24);
my @sorted_array = sort { $a <=> $b } @array;
print join("<", @sorted_array), "\n";
[liuguiyou@localhost perl]$ ./sort.pl
  -7<5<8<8<10<24<29<34<58<92<100

Much more civil, isn't it? The following example, sorts an array of strings in reverse:

[liuguiyou@localhost perl]$ cat sort_chara.pl
  #!/usr/bin/perl
use strict;
  use warnings;
my @input = (
      "Hello World!",
      "You is all I need.",
      "To be or not to be",
      "There's more than one way to do it.",
      "Absolutely Fabulous",
      "Ci vis pacem, para belum",
      "Give me liberty or give me death.",
      "Linux - Because software problems should not cost money",
  );
# Do a case-insensitive sort
  my @sorted = sort { lc($a) cmp lc($b); } @input;
print join("\n", @sorted), "\n";
[liuguiyou@localhost perl]$ ./sort_chara.pl
  Absolutely Fabulous
  Ci vis pacem, para belum
  Give me liberty or give me death.
  Hello World!
  Linux - Because software problems should not cost money
  There's more than one way to do it.
  To be or not to be
  You is all I need.