In Perl, a comparison operator for numbers, similar to the string comparison operator 'cmp'.

<=> and cmp return:

• -1 if left operand less than right operand
• 0 if operands are equal
• 1 if left operand greater than right operand

These returns are the same as strcmp in C.

The <=> operand is known as the spaceship operator, for reasons that should be obvious if you have seen Star Wars.

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In maths (esp. logic), "<=>" means double implication, an implication that goes both ways. In other words,

A <=> B

means the same as

A => B and B => A

"<=>" is often read as "if and only if".