Use the parentheses operator linuxshell "()"

The shell () double bracket operator uses four arithmetic operations and logical operations for inuxshell script programming at the beginning. It is estimated that many friends feel unacceptable. When using the special variable logical operator [], there must be a space between the operator and arithmetic. 4...
The linux shell "()" double-bracket operator uses four arithmetic operations and logical operations for inux shell script programming at the beginning. It is estimated that many friends feel unacceptable. When using the special variable logical operator "[]", there must be a space between the operator and arithmetic. The four arithmetic operations can only be completed by using commands such as: let and expr. The double parentheses () structure statement described today is an extension of the arithmetic and value assignment operations in shell. Usage: syntax: www.2cto.com (expression 1, expression 2 ...)) Features: 1. in the double-bracket structure, all expressions can be the same as those in the C language, such as a ++ and B. 2. in the double-bracket structure, all variables can be prefixed with the "$" symbol. 3. you can perform logical operations with double parentheses. 4. the double parentheses structure extends the for, while, and if conditions. 5. multiple expressions are supported. each expression uses ", "Use instances separately: expand the four arithmetic operations #! /Bin/sh a = 1; B = 2; c = 3; (a = a + 1); echo $ a; a = $ (a + 1, B ++, c ++); echo $ a, $ B, $ c running result: sh testsh. multiple expressions are supported between the, and 4 double-bracket structures at www.2cto.com. common operators such as addition, subtraction, multiplication, division, and so on are supported. If the brackets are: $, the expression value is obtained and assigned to the left variable. Extended logical operations #! /Bin/sh a = 1; B = "AB"; echo $ (a> 1? 8: 9); (B! = "A") & echo "err2"; (a <2) & echo "OK"; running result: sh testsh. sh9 www.2cto.com err2ok extended process control statement (logical relationship )#! /Bin/sh num = 100; total = 0; for (I = 0; I <= num; I ++); do (total + = I )); doneecho $ total; total = 0; I = 0; while (I <= num); do www.2cto.com (total + = I, I ++ )); doneecho $ total; if (total> = 5050); then echo "OK"; fi operation result: sh testsh. sh50505050ok has the double-bracket operator [[], [], and test, which can be left to one side by let and expr.

Address: http://www.cnblogs.com/chengmo/archive/2010/10/19/1855577.html #