------------------------
不像其他程序语言一样,Bash并不对变量区分"类型".本质上,Bash变量都是字符串.但是依赖于上下文,Bash也允许比较操作和算术操作.决定这些的关键因素就是,变量中的值是否只有数字.
Example 4-4 整型还是string?
################################Start Script#######################################
1 #!/bin/bash
2 # int-or-string.sh: 整形还是string?
3
4 a=2334 # 整型
5 let "a += 1"
6 echo "a = $a " # a = 2335
7 echo # 还是整型
8
9
10 b=${a/23/BB} # 将23替换成BB
11 # 这将把b变量从整型变为string
12 echo "b = $b" # b = BB35
13 declare -i b # 即使使用declare命令也不会对此有任何帮助,9.4节有解释
14 echo "b = $b" # b = BB35
15
16 let "b += 1" # BB35 + 1 =
17 echo "b = $b" # b = 1
18 echo
19
20 c=BB34
21 echo "c = $c" # c = BB34
22 d=${c/BB/23} # S将BB替换成23
23 # 这使得$d变为一个整形
24 echo "d = $d" # d = 2334
25 let "d += 1" # 2334 + 1 =
26 echo "d = $d" # d = 2335
27 echo
28
29 # 关于空变量怎么样?
30 e=""
31 echo "e = $e" # e =
32 let "e += 1" # 算术操作允许一个空变量?
33 echo "e = $e" # e = 1
34 echo # 空变量将转换成一个整型变量
35
36 # 关于未声明的变量怎么样?
37 echo "f = $f" # f =
38 let "f += 1" # 算术操作允许么?
39 echo "f = $f" # f = 1
40 echo # 未声明的变量将转换成一个整型变量
41
42
43
44 # 所以说Bash中的变量都是无类型的.
45
46 exit 0
################################End Script######################################### |