php版本比較函數version_compare()

php中比較php版本，一般用version_compare()函數，協助文檔見：http://php.net/manual/en/function.version-compare.php
用途：Compares two "PHP-standardized" version number
strings。
文法：
version_compare

( string
$version1

, string
$version2

[, string
$operator

] )
具體描述：version_compare()

compares two
"PHP-standardized"
version number strings. This is useful if you would like to write
programs
working only on some versions of PHP.

The function first replaces _
, -
and
+
with a dot .
in the version
strings and also inserts dots .
before and after any
non number so that for example '4.3.2RC1' becomes '4.3.2.RC.1'. Then
it
splits the results like if you were using explode('.', $ver). Then it
compares the parts starting from left to right. If a part contains
special version strings these are handled in the following order:
any string not found in this list
<
dev
< alpha
=
a
< beta
=
b
< RC
=
rc
< #
<
pl
= p
. This way not only versions
with different levels like '4.1' and '4.1.2' can be compared but also
any
PHP specific version containing development state.

    其中第三個選擇性參數是比較符：

If you specify the third optional operator

argument, you can test for a particular relationship. The
possible operators are: <
,
lt
, <=
,
le
, >
,
gt
, >=
,
ge
, ==
,
=
, eq
,
!=
, <>
,
ne
respectively.

This parameter is case-sensitive, so values should be lowercase.

    傳回值：

By default, version_compare()

returns
-1
if the first version is lower than the second,
0
if they are equal, and
1
if the second is lower.

When using the optional operator

argument, the
function will return TRUE

if the relationship is the
one specified
by the operator, FALSE

otherwise.

    從下面的例子，就可以很好地說明version_compare的用法：


<?php

if (
version_compare
(
PHP_VERSION
, 
'6.0.0'
) >= 
0
) {
    echo 
'I am at least PHP version 6.0.0, my version: ' 
. 
PHP_VERSION 
. 
"/n"
;
}

if (
version_compare
(
PHP_VERSION
, 
'5.3.0'
) >= 
0
) {
    echo 
'I am at least PHP version 5.3.0, my version: ' 
. 
PHP_VERSION 
. 
"/n"
;
}

if (
version_compare
(
PHP_VERSION
, 
'5.0.0'
, 
'>='
)) {
    echo 
'I am using PHP 5, my version: ' 
. 
PHP_VERSION 
. 
"/n"
;
}

if (
version_compare
(
PHP_VERSION
, 
'5.0.0'
, 
'<'
)) {
    echo 
'I am using PHP 4, my version: ' 
. 
PHP_VERSION 
. 
"/n"
;
}

?>

    最近在nagios的圖表監控外掛程式pnp安裝中遇到一個錯誤提示：Kohana requires PHP 5.2 or newer.查看頁面源碼，發現如下語句：
version_compare(PHP_VERSION, '5.2', '<') and exit('Kohana requires PHP 5.2 or newer.');
也就是版本不滿足就退出。