basic elements: istrue isfalse not and or xor available isset equals filesmatch
1、istrue isfalse:断言 真 假
is ture
is false
2、逻辑运算
2.1、not 逻辑非
＜not>
is ture
is false
2.2、and 逻辑与
＜and>
is ture
is false
2.3、or 逻辑或 xor异或 (语法上与and类似)
3、available 是否可用
is ture
is false
4、isset 指定属性是否存在
is ture
is false
5、equals 是否相等
is ture
is false
6、filesmatch 比较文件
is ture
is false
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