# sed替换行首和行尾

我一直以为，用`^`和`$`来代表行首和行尾，用`sed`可以很容易实现替换行首和行尾，但是没有想到还有一个`&`符号(可能还是需要根据`sed`版本， `gsed (GNU sed) 4.8` 我验证加不加 `&` 都一样)，实际方法如下：

```bash
sed -i 's/^/HEAD&/g' test.file

sed -i 's/$/&TAIL/g' test.file
```

> `-i`参数直接修改原文件
>
> `g`表示每行出现的匹配字符全部替换，否则就只替换每行的第一个匹配字符

上述命令在每一行的前面添加 `HEAD` ，以及在每一行的末尾添加 `TAIL` 。例如，对于 `test.file` ，原先内容是:

```bash
abcd
ab cd
```

执行以后内容修改为

```bash
HEADabcdTAIL
HEADab cdTAIL
```

上述两条命令可以结合成一起使用

```bash
sed '/./{s/^/HEAD&/;s/$/&TAIL/}' test.file
```

## 参考

* [linux shell 用sed命令在文本的行尾或行首添加字符](http://www.cnblogs.com/aaronwxb/archive/2011/08/19/2145364.html)


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