# cat: 连接

`cat`输出文件内容，到标准输出或另一个文件里面。

### **实例1：查看单个文件**

```bash
cat filename
```

这会打印文件所有的内容到屏幕上。

### **实例2：查看多个文件**

```bash
cat file1 file2
```

将打印多个文件。

### **实例3：输出行号**

```bash
cat -n filename
```

不但打印出文件内容，还会在每行前面打印行号。

### **实例4：新建一个文件**

```bash
cat > newfile
```

这样会新建一个文件，这个时候输入的内容就会写入文件，然后Ctrl+c退出。

### **实例5：复制文件**

```bash
cat src-filename > dest-filename
```

这会把`src-filename`复制到新的`dest-filename`中。

### **实例6：压缩空行**

```bash
cat -s filename
```

如果文件中有空行，会对其进行压缩（连续多个空行只输出一行）。

### **实例7：添加内容**

```bash
cat src-filename >> desc-filename
```

这会把`src-filename`的内容添加到`desc-filename`文件的末尾。

### **实例8：文件拼接**

根据7可以实现多个文件的拼接：

```bash
cat file1 file2 file3 ... filen >> file
```


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