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# 环境变量
<a name="example-use-envvars"></a>

以下作业定义示例使用环境变量来指定文件类型和 Amazon S3 URL。该特定示例来自[创建简单的“Fetch & Run”Amazon Batch 作业](https://www.amazonaws.cn/blogs/compute/creating-a-simple-fetch-and-run-aws-batch-job/)计算博客文章。博客文章中描述的[https://github.com/awslabs/aws-batch-helpers/blob/master/fetch-and-run/fetch_and_run.sh](https://github.com/awslabs/aws-batch-helpers/blob/master/fetch-and-run/fetch_and_run.sh)脚本使用这些环境变量从 S3 下载`myjob.sh`脚本并声明其文件类型。

尽管在本示例中，命令和环境变量被硬编码到作业定义中，但仍可指定命令和环境变量覆盖，使作业定义更具通用性。

```
{
    "jobDefinitionName": "fetch_and_run",
    "type": "container",
    "containerProperties": {
        "image": "{{123456789012}}.dkr.ecr.us-east-1.amazonaws.com/fetch_and_run",
        "resourceRequirements": [
            {
                "type": "MEMORY",
                "value": "2000"
            },
            {
                "type": "VCPU",
                "value": "2"
            }
        ],
        "command": [
            "myjob.sh",
            "60"
        ],
        "jobRoleArn": "arn:aws:iam::{{123456789012}}:role/AWSBatchS3ReadOnly",
        "environment": [
            {
                "name": "BATCH_FILE_S3_URL",
                "value": "s3://amzn-s3-demo-source-bucket/myjob.sh"
            },
            {
                "name": "BATCH_FILE_TYPE",
                "value": "script"
            }
        ],
        "user": "nobody"
    }
}
```