440 lines
7.5 KiB
Markdown
440 lines
7.5 KiB
Markdown
<h2><center>awk 流程控制</center></h2>
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------
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## 一：流程控制
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### 1. 条件
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#### 1. if 语句
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**`if`条件语句语法格式**
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```shell
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if (condition)
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action
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```
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**使用花括号语法格式**
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```shell
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if (condition)
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{
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action1;
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action2;
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...
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}
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{if(表达式)｛语句1;语句2;...｝}
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```
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**示例：**
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判断数字是奇数还是偶数
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```bash
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[root@wxin ~]# awk 'BEGIN {num = 10; if (num % 2 == 0) printf "%d 是偶数\n", num }'
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10 是偶数
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```
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判断 root 是不是 administrator
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```bash
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[root@wxin ~]# awk -F: '{if($3==0) {print $1 " is administrator."}}' /etc/passwd
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root is administrator.
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```
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统计系统用户数
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```bash
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[root@wxin ~]# awk -F: '{if($3>0 && $3<1000){count++;}} END{print count}' /etc/passwd
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20
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```
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#### 2. if - else 语句
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**`if - else`条件语句语法格式**
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```shell
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if (condition)
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action1
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else
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action2
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```
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**使用花括号语法格式**
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```shell
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{if (condition)
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{
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action1;
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action2;
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...
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}
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else
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{
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action1;
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action2;
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...
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}}
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{if(表达式)｛语句1;语句2;...｝else{语句1;语句2;...}}
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```
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**示例：**
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判断数字是奇数还是偶数
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```bash
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[root@wxin ~]# awk 'BEGIN {
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num = 11;
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if (num % 2 == 0) printf "%d 是偶数\n", num;
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else printf "%d 是奇数\n", num
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}'
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11 是奇数
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```
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判断用户为root就打印用户名否则打印shell类型
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```bash
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[root@wxin ~]# awk -F: '{if($3==0){print $1} else {print $7}}' /etc/passwd
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root
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/sbin/nologin
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/sbin/nologin
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/sbin/nologin
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/sbin/nologin
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/bin/sync
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/sbin/shutdown
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```
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统计管理员数量和系统用户数量
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```bash
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[root@wxin ~]# awk -F: '{if($3==0){count++} else{i++}} END{print "管理员个数: "count ; print "系统用户数: "i}' /etc/passwd
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管理员个数: 1
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系统用户数: 20
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```
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#### 3. if - else - if 语句
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**`if - else - if`条件语句语法格式**
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```shell
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{if (condition1)
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{
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action1;
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action2;
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...
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}
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else if (condition2)
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{
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action1;
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action2;
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...
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}
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else if (condition3)
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{
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action1;
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action2;
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...
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}
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else
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{
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action1;
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action2;
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...
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}}
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{if(表达式1)｛语句1;语句2；...｝else if(表达式2)｛语句1;语句2；...｝else if(表达式3)｛语句1;语句2；...｝else｛语句1;语句2；...｝}
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```
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**示例：**
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多级判断结果
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```bash
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[root@wxin ~]# awk 'BEGIN {
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a=30;
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if (a==10)
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print "a = 10";
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else if (a == 20)
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print "a = 20";
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else if (a == 30)
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print "a = 30";
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}'
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a = 30
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```
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统计管理员，系统，普通用户数量
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```bash
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[root@wxin ~]# awk -F: '{if($3==0){i++} else if($3>999){k++} else{j++}} END{print i; print k; print j}' /etc/passwd
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1
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20
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[root@wxin ~]# awk -F: '{if($3==0){i++} else if($3>999){k++} else{j++}} END{print "管理员个数: "i; print "普通用个数: "k; print "系统用户: "j}' /etc/passwd
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管理员个数: 1
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普通用个数:
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系统用户: 20
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```
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### 2. 循环
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#### 1. for 循环
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**语法：**
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```shell
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for(variable addignment; condition; iteration peocess)
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{
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statement1
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statement2
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...
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}
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```
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for 语句首先执行初始化动作( initialisation )，然后再检查条件( condition )。如果条件为真，则执行动作( action )，然后执行递增( increment )或者递减( decrement )操作。只要条件为 true 循环就会一直执行。每次循环结束都会进条件检查，若条件为 false 则结束循环。
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**示例：**
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For 循环输出数字 1 至 5
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```bash
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[root@wxin ~]# awk 'BEGIN { for (i = 1; i <= 5; ++i) print i }'
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1
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2
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3
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4
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5
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```
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For 循环输出数字 1 至 9 的奇数之和
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```bash
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[root@wxin ~]# echo "hello" | awk '
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{
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total = 0
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for(i=1; i<10; i++)
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{
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if(i % 2 == 0)
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{
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continue
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}
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total = total + i
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}
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print "total=", total
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}'
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```
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将每行打印10次
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```bash
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[root@wxin ~]# awk -F: '{ for(i=1;i<=10;i++) {print $0} }' /etc/passwd
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root:x:0:0:root:/root:/bin/bash
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root:x:0:0:root:/root:/bin/bash
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root:x:0:0:root:/root:/bin/bash
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root:x:0:0:root:/root:/bin/bash
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root:x:0:0:root:/root:/bin/bash
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root:x:0:0:root:/root:/bin/bash
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root:x:0:0:root:/root:/bin/bash
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root:x:0:0:root:/root:/bin/bash
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root:x:0:0:root:/root:/bin/bash
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root:x:0:0:root:/root:/bin/bash
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```
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分别打印每行的每列
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```bash
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[root@wxin ~]# awk -F: '{ for(i=1;i<=NF;i++) {print $i} }' /etc/passwd
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root
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x
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0
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0
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root
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/root
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/bin/bash
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bin
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x
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1
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1
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bin
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/bin
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/sbin/nologin
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```
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#### 2. while 循环
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**语法：**
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```shell
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while(condition)
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{
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statement1
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statement2
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...
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}
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```
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While 循环首先检查条件 condition 是否为 true ，若条件为 true 则执行动作 action。此过程一直重复直到条件 condition 为 flase 才停止。
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**示例：**
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While 循环输出数字 1 到 5
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```bash
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[root@wxin ~]# awk 'BEGIN {i = 1; while (i < 6) { print i; ++i } }'
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1
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2
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3
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4
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5
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[root@wxin ~]# awk 'BEGIN{ i=1; while(i<=5){print i; i++} }'
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1
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2
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3
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4
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5
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```
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While 循环输出数字 1 至 9 的奇数之和
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```bash
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[root@wxin ~]# echo "hello" | awk '
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{
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total = 0
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i = 1
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while(i < 10)
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{
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if(i % 2 == 0)
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{
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i++
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continue
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}
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total = total + i
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i++
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}
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print "total=", total
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}'
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```
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打印第一行的前七列
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```bash
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[root@wxin ~]# awk -F: '/^root/{i=1; while(i<=7){print $i; i++}}' /etc/passwd
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root
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x
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0
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0
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root
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/root
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/bin/bash
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```
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分别打印每行的每列
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```bash
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[root@wxin ~]# awk '{i=1; while(i<=NF){print $i; i++}}' /etc/hosts
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127.0.0.1
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localhost
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localhost.localdomain
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localhost4
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localhost4.localdomain4
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::1
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localhost
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localhost.localdomain
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localhost6
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localhost6.localdomain6
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```
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#### 3. break 结束循环
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break[n]：当第n次循环到来后，结束整个循环，n=0就是指本次循环
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当计算的和大于 50 的时候使用 break 结束循环：
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```bash
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[root@wxin ~]# awk 'BEGIN {
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sum = 0; for (i = 0; i < 20; ++i) {
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sum += i; if (sum > 50) break; else print "Sum =", sum
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}
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}'
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Sum = 0
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Sum = 1
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Sum = 3
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Sum = 6
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Sum = 10
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Sum = 15
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Sum = 21
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Sum = 28
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Sum = 36
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Sum = 45
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```
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#### 4. continue 跳出本次循环
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Continue 语句用于在循环体内部结束本次循环，从而直接进入下一次循环迭代。
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Continue[n]：满足条件后，直接进行第n次循环，本次循环不在进行，n=0也就是提前结束本次循环而直接进入下一轮
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输出 1 到 20 之间的偶数：
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```bash
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[root@wxin ~]# awk 'BEGIN {for (i = 1; i <= 20; ++i) {if (i % 2 == 0) print i ; else continue} }'
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2
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4
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6
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8
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10
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12
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14
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16
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18
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20
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```
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#### 5. exit 结束脚本程序
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Exit 用于结束脚本程序的执行。
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该函数接受一个整数作为参数表示 AWK 进程结束状态。 如果没有提供该参数，其默认状态为 0。
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当和大于 50 时结束 AWK 程序。
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```bash
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[root@wxin ~]# awk 'BEGIN {
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sum = 0; for (i = 0; i < 20; ++i) {
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sum += i; if (sum > 50) exit(10); else print "Sum =", sum
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}
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}'
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Sum = 0
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Sum = 1
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Sum = 3
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Sum = 6
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Sum = 10
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Sum = 15
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Sum = 21
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Sum = 28
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Sum = 36
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Sum = 45
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```
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检查脚本执行后的返回状态
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```bash
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[root@wxin ~]# echo $?
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10
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```
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#### 6. next 停止处理
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next：提前结束对本行的处理动作而直接进入下一行处理
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```bash
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[root@wxin ~]# awk -F: '{if($3%2!=0) next; print $1,$3}' /etc/passwd
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``` |