双圆括号结构
与let命令很相似, ((...))结构允许算术扩展和赋值. 举个简单的例子, a=$(( 5 + 3 )), 将把变量"a"设为"5 + 3", 或者8. 然而, 双圆括号结构也被认为是在Bash中使用C语言风格变量操作的一种处理机制.
#!/bin/bash (( a = 23 )) # C语言风格的变量赋值,"="两边允许有空格. echo "a (initial value) = $a" (( a++ )) # C语言风格的后置自加. echo "a (after a++) = $a" (( a-- )) # C语言风格的后置自减. echo "a (after a--) = $a" (( ++a )) # C语言风格的前置自加. echo "a (after ++a) = $a" (( --a )) # C语言风格的前置自减. echo "a (after --a) = $a" (( t = a<45?7:11 )) # C语言风格的三元操作. echo "If a < 45, then t = 7, else t = 11." echo "t = $t " exit 0
结果：
root@ubuntu:~/resource/0510# ./test1 a (initial value) = 23 a (after a++) = 24 a (after a--) = 23 a (after ++a) = 24 a (after --a) = 23 If a < 45, then t = 7, else t = 11. t = 7 root@ubuntu:~/resource/0510#
待续。。。。。