awk - 数据提取和报告工具 (2) 进阶
Synopsis: 详细描述了awk编程语言的基础语法，其中操作符和正则表达式组合后，即为awk中的匹配模式。action是一系列的执行语句，一般包括赋值语句、条件语句、循环语句、输入/输出语句等。awk数组也叫关联数组，其下标既可以是数字也可以是字符串，awk提供了逻辑上模拟二维数组的访问方式，其本质上还是一维数组。可以将数据重定向到一个文件，重定向出现在print或printf语句之后。awk中的重定向与shell命令中的重定向一样，只是它们写在awk程序中。要输出美观的报告，printf格式化怎么少得了
awk系列：
- awk - 数据提取和报告工具 (1) 入门
- awk - 数据提取和报告工具 (2) 进阶 [current]
- awk - 数据提取和报告工具 (3) 函数
- awk - 数据提取和报告工具 (4) 实战
1. 操作符
1.1 算术运算符
1. 加 # awk 'BEGIN { a = 50; b = 20; print "(a + b) = ", (a + b) }' (a + b) = 70 2. 减 # awk 'BEGIN { a = 50; b = 20; print "(a - b) = ", (a - b) }' (a - b) = 30 3. 乘 # awk 'BEGIN { a = 50; b = 20; print "(a * b) = ", (a * b) }' (a * b) = 1000 4. 除 # awk 'BEGIN { a = 50; b = 20; print "(a / b) = ", (a / b) }' (a / b) = 2.5 5. 余数 # awk 'BEGIN { a = 50; b = 20; print "(a % b) = ", (a % b) }' (a % b) = 10 6. 指数 # awk 'BEGIN { a = 10; a = a ^ 2; print "a =", a }' a = 100 或者: # awk 'BEGIN { a = 10; a = a**2; print "a =", a }' a = 100
1.2 递增和递减运算符
1. 先自增，再赋值 # awk 'BEGIN { a = 10; b = ++a; printf "a = %d, b = %d\n", a, b }' a = 11, b = 11 2. 先自减，再赋值 # awk 'BEGIN { a = 10; b = --a; printf "a = %d, b = %d\n", a, b }' a = 9, b = 9 3. 先赋值，再自增 # awk 'BEGIN { a = 10; b = a++; printf "a = %d, b = %d\n", a, b }' a = 11, b = 10 4. 先赋值，再自减 # awk 'BEGIN { a = 10; b = a--; printf "a = %d, b = %d\n", a, b }' a = 9, b = 10
1.3 复合赋值运算符
1. 简单赋值 # awk 'BEGIN { name = "Jerry"; print "My name is", name }' My name is Jerry 2. 左边变量加上右边的值，再赋值给左边的变量 # awk 'BEGIN { cnt = 10; cnt += 10; print "Counter =", cnt }' Counter = 20 3. 左边变量减去右边的值，再赋值给左边的变量 # awk 'BEGIN { cnt = 100; cnt -= 10; print "Counter =", cnt }' Counter = 90 4. 左边变量乘以右边的值，再赋值给左边的变量 # awk 'BEGIN { cnt = 10; cnt *= 10; print "Counter =", cnt }' Counter = 100 5. 左边变量除以右边的值，再赋值给左边的变量 # awk 'BEGIN { cnt = 100; cnt /= 5; print "Counter =", cnt }' Counter = 20 6. 左边变量与右边的值求余数，再赋值给左边的变量 # awk 'BEGIN { cnt = 100; cnt %= 8; print "Counter =", cnt }' Counter = 4 7. 左边变量为底数，右边的值为指数，求出指数，再赋值给左边的变量 # awk 'BEGIN { cnt = 2; cnt ^= 4; print "Counter =", cnt }' Counter = 16 或者: # awk 'BEGIN { cnt = 2; cnt **= 4; print "Counter =", cnt }' Counter = 16
1.4 关系运算符
表达式成立时返回true，执行后续的命令；否则返回false，不执行后续的命令
# awk 'BEGIN { a = 10; b = 10; if (a == b) print "a == b" }' a == b # awk 'BEGIN { a = 10; b = 20; if (a != b) print "a != b" }' a != b # awk 'BEGIN { a = 10; b = 20; if (a < b) print "a < b" }' a < b # awk 'BEGIN { a = 10; b = 10; if (a <= b) print "a <= b" }' a <= b # awk 'BEGIN { a = 10; b = 20; if (b > a ) print "b > a" }' b > a # awk 'BEGIN { a = 10; b = 10; if (b >= a ) print "b >= a" }' b >= a
1.5 逻辑运算符
1. expr1 && expr2 逻辑与，同时为真时结果才为真。也叫短路与，当且仅当expr1为真时，才验证expr2 # awk 'BEGIN { num = 5; if (num >= 0 && num <= 7) printf "%d is in octal format\n", num }' 5 is in octal format 2. expr1 || expr2 逻辑或，只要一个为真结果就为真。也叫短路或，当且仅当expr1为假时，才验证expr2 # awk 'BEGIN { ch = "\n"; if (ch == " " || ch == "\t" || ch == "\n") print "Current character is whitespace." }' Current character is whitespace. 3. ! expr1 逻辑非，取反，当expr1为真时，结果为0；当expr1为假时，结果为1。说明: awk中0代表false，非0代表true # awk 'BEGIN { name = ""; if (! length(name)) print "name is empty string." }' name is empty string.
1.6 三元运算符
语法为condition expression ? statement1 : statement2，如果表达式返回真，则执行statement1，否则执行statement2
1.7 正负号
负数的负数是正数
# awk 'BEGIN { a = -10; a = +a; print "a =", a }' a = -10 # awk 'BEGIN { a = -10; a = -a; print "a =", a }' a = 10
1.8 字符串连接运算符
空格是合并两个字符串的字符串连接运算符。
1.9 数组成员操作符
未经允许不得转载: LIFE & SHARE - 王颜公子 » awk - 数据提取和报告工具 (2) 进阶
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