> For the complete documentation index, see [llms.txt](https://camelgemonion.gitbook.io/docker/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://camelgemonion.gitbook.io/docker/dockerfile-zhi-ling/parser-directives.md).

# Parser directives

## Parser directives

**解析器指令**是可选的，并且会影响**Dockerfile**中后续行的处理方式。**解析器指令**不会在构建中添加镜像层，也不会在构建步骤中显示。**解析器指令以＃指令=值的形式写为特殊的注释类型。**单个指令只能使用一次。

**处理完注释，空行或构建器指令后，Docker不再寻找解析器指令，而是将格式化为解析器指令的任何内容都视为注释，并且不会尝试验证它是否可能是解析器指令。因此，所有解析器指令必须位于Dockerfile的最顶部。**

**解析器指令**不区分大小写。但是根据约定是小写的。约定还包括应在任何**解析器指令**之后包含一个空白行。**解析器指令**不支持行继续符。

由于这些规则，以下示例均无效：

由于行继续符而无效：

```
# direc \
tive=value
```

下面的指令无效的，因为出现了两次

```
# directive=value1
# directive=value2

FROM ImageName
```

会被当成注释，因为解析器指令出现在了构建器指令后面

```
FROM ImageName
# directive=value
```

会被当成注释，因为解析器指令出现在了注释后面

```
# About my dockerfile
# directive=value
FROM ImageName
```

由于无法被识别，未知指令被视为注释。另外，由于在不是**解析器指令**的注释之后出现，所以已知指令被视为注释。

```
# unknowndirective=value  #无法被识别，因此当成注释
# knowndirective=valuev  #由于前面的指令备当成了注释，出现在注释后面的解析器指令被当成注释对待。
```

**解析器指令**中允许使用不换行的空格。因此，以下各行都被相同地对待：

```
#directive=value
# directive =value
#    directive= value
# directive = value
#      dIrEcTiVe=value
```

以下两个指令是支持的**解析器指令**:

* **syntax**
* **escape**


---

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