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2.4.2 Comparison Operators

Comparing two scalars is quite easy in Perl. The numeric comparison operators that you would find in C, C++, or Java are available. However, since Perl does automatic conversion between strings and numbers for you, you must differentiate for Perl between numeric and string comparison. For example, the scalars "532" and "5" could be compared two different ways--based on numeric value or ASCII string value.

The following table shows the various comparison operators and what they do. Note that in Perl "", 0 and undef are false and anything else as true. (This is an over-simplified definition of true and false in Perl. See section A Digression--Truth Values, for a complete definition.)

The table below assumes you are executing $left <OP> $right, where <OP> is the operator in question.

Operation	Numeric Version	String Version	Returns
less than	`<`	`lt`	1 iff. `$left` is less than `$right`
less than or equal to	`<=`	`le`	1 iff. `$left` is less than or equal to `$right`
greater than	`>`	`gt`	1 iff. `$left` is greater than `$right`
greater than or equal to	`>=`	`ge`	1 iff. `$left` is greater than or equal to `$right`
equal to	`==`	`eq`	1 iff. `$left` is the same as `$right`
not equal to	`!=`	`ne`	1 iff. `$left` is not the same as `$right`
compare	`<=>`	`cmp`	-1 iff. `$left` is less than `$right`, 0 iff. `$left` is equal to `$right` 1 iff. `$left` is greater than `$right`

Here are a few examples using these operators.

use strict;
my $a = 5; my $b = 500;
$a < $b;                 # evaluates to 1
$a >= $b;                # evaluates to ""
$a <=> $b;               # evaluates to -1
my $c = "hello"; my $d = "there";
$d cmp $c;               # evaluates to 1
$d ge  $c;               # evaluates to 1
$c cmp "hello";          # evaluates to ""