# seq: 生成序列

`seq`命令用于生成一个序列，从*FIRST*开始以*INCREMENT*为间隔到*LAST*。`seq`命令在shell脚本中的for循环中很有用。

## 1. 命令格式

```
seq [OPTION]... LAST
seq [OPTION]... FIRST LAST
seq [OPTION]... FIRST INCREMENT LAST
```

## 2. 参数

| 参数                       | 含义           |
| ------------------------ | ------------ |
| -f, --format=*FORMAT*    | 打印的格式        |
| -s, --separator=*STRING* | 分隔符，默认换行     |
| -w, --equal-width        | 生成等长的序列，用0填充 |

## 3. 使用示例

### **实例1：生成1到10的序列**

```
seq 1 5
seq 5
```

结果：

```
1
2
3
4
5
```

如果初始值是1，那么可以忽略，`seq`的*FIRST*默认就是1。

### **实例2：生成1到10的偶数序列**

```
seq 2 2 10
```

结果：

```
2
4
6
8
10
```

### **实例3：小数步长**

```
seq 1 0.5 2
```

结果：

```
1.0
1.5
2.0
```

步长默认是1，不过也可以设置成其它值。

### **实例4：对LAST的处理**

```
seq 3 7 30
```

结果：

```
3
10
17
24
```

序列最后一个值小于等于*LAST*。

### **实例5：格式化输出**

```
seq -f "GFG%02g" 4
```

结果：

```
GFG01
GFG02
GFG03
GFG04
```

### **实例6：分隔符**

```
seq -s " " 10        // 1 2 3 4 5 6 7 8 9 10
seq -s " " 5 10      // 5 6 7 8 9 10
seq -s "-" 5 4 15    // 5-9-13
```

### **实例7：等长输出**

```
seq -w 10
```

结果：

```
01
02
03
04
05
06
07
08
09
10
```

```
seq -w 99 101
```

结果：

```
099
100
101
```

```
seq -w 1 10 50
```

结果：

```
01
11
21
31
41
```

### **实例8：在for中使用**

```
for i in `seq 10`
do
    echo $i
done
```


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