shell的问题

共有 2 条评论

1. wucongdonglai 于 2010-10-25 14:18:08发表:

   2# deepwhite
   恩，谢white兄

2. deepwhite 于 2010-10-25 11:30:52发表:

   [i=s] 本帖最后由 deepwhite 于 2010-10-25 11:34 编辑 [/i]
   
   前面两个都对，最后一个， d=$((d-1)) 这么写也是可以的。可以看看 bash reference 或者自己实验一下。
   
   

   引用:

   
   3.5.5 Arithmetic Expansion
   
   Arithmetic expansion allows the evaluation of an arithmetic expression and the substitution of the result. The format for arithmetic expansion is:
   
   $(( expression ))
   The expression is treated as if it were within double quotes, but a double quote inside the parentheses is not treated specially. All tokens in the expression undergo parameter expansion, command substitution, and quote removal. Arithmetic expansions may be nested.
   
   The evaluation is performed according to the rules listed below (see Shell Arithmetic). If the expression is invalid, Bash prints a message indicating failure to the standard error and no substitution occurs.
   

   
   [code]
   deepwhite@local ~ $ a=1 && echo $((a+3))
   4
   [/code]