How do I run a shell script in a Lambda function?

Question

I have a '.sh' file in my s3 storage to be run via a lambda function using Python 3.11. I found a code snippet shared below but it throws an error saying that there is no path as such. What's the correct way of running a shell script using Python inside a Lambda function?

```
import subprocess
try:
    subprocess.run(script_path, shell=True)
except Exception as e:
    print(f"Error running shell script: {e}")
```

Answer

Hello.

If a shell script file exists in S3, I think it is necessary to retrieve the shell script from S3 using download_file() and then execute it.

The code below downloads a shell script from S3 to Lambda's temporary folder.  
I also run the "chmod" command to change the permissions of the shell script.  
```
import subprocess
import boto3

s3 = boto3.client('s3')
bucket_name = 'testbucket'
key = 'example.sh'
script_path = '/tmp/local_example.sh'

def lambda_handler(event, context):

s3.download_file(bucket_name, key, script_path)
    try:
        subprocess.run(["chmod","755",script_path])
        subprocess.run(script_path, shell=True)
    except Exception as e:
        print(f"Error running shell script: {e}")
```

Please set the following IAM policy for the Lambda IAM role to download the shell script from S3.  
```
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": "s3:GetObject",
            "Resource": "*"
        }
    ]
}
```

Answer

This also walks through the steps to create a custom runtime to execute a bash script. [Tutorial – Publishing a custom runtime](https://docs.aws.amazon.com/lambda/latest/dg/runtimes-walkthrough.html)

Answer

Hi,

May I advertise one of my personal projects ? https://github.com/didier-durand/lambda-cobol

It creates a Custom Lambda runtime able to run a bash shell to launch the Cobol program. So, if you replicate this setup, you will be able to run any shell script.

Have a look at lambda-cobol.sh and how it is triggered to replicate that in your own use case.

Best,

Didier

How do I run a shell script in a Lambda function?

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