lambda_function.py

# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
# SPDX-License-Identifier: Apache-2.0
import json
import urllib.parse
import boto3
import os

print('Loading function')

s3 = boto3.client('s3')

def lambda_handler(event, context):
    for record in event['Records']:
        # Skip if this event was generated by Lambda
        if record.get('userIdentity', {}).get('principalId', '').endswith(':aws:lambda'):
            print("Skipping Lambda-generated event to prevent recursion")
            continue
            
        bucket = record['s3']['bucket']['name']
        key = record['s3']['object']['key']
            
        try:
            # Get the object
            response = s3.get_object(Bucket=bucket, Key=key)
            content = response['Body'].read().decode('utf-8')
            
            # Split into lines and modify first line
            lines = content.splitlines(keepends=True)
            if len(lines) > 0:
                print(f"First line of {key}: '{lines[0].strip()}'")
                if (lines[0].strip() == 'abc'):
                    lines[0] = "def\n"
                
            # Upload to different location to prevent recursion
            s3.put_object(
                Bucket='myawsbucket-lambda-output',
                Key=key,
                Body=''.join(lines),
                Metadata=response.get('Metadata', {}),
                ContentType=response.get('ContentType', 'text/plain')
            )
            
        except Exception as e:
            print(e)
            print('Error getting object {} from bucket {}. Make sure they exist and your bucket is in the same region as this function.'.format(key, bucket))
            raise e