Write logs

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Writes a Cloud Functions log entry.

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For detailed documentation that includes this code sample, see the following:

Code sample


using Google.Cloud.Functions.Framework;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using System;
using System.Threading.Tasks;

namespace LogHelloWorld
    public class Function : IHttpFunction
        private readonly ILogger _logger;

        public Function(ILogger<Function> logger) =>
            _logger = logger;

        public async Task HandleAsync(HttpContext context)
            Console.WriteLine("I am a log to stdout!");
            Console.Error.WriteLine("I am a log to stderr!");

            _logger.LogInformation("I am an info log!");
            _logger.LogWarning("I am a warning log!");

            await context.Response.WriteAsync("Messages successfully logged!");


// Package helloworld provides a set of Cloud Functions samples.
package helloworld

import (

// HelloLogging logs messages.
func HelloLogging(w http.ResponseWriter, r *http.Request) {
	log.Println("This is stderr")
	fmt.Println("This is stdout")

	// Structured logging can be used to set severity levels.
	// See https://cloud.google.com/logging/docs/structured-logging.
	fmt.Println(`{"message": "This has ERROR severity", "severity": "error"}`)

	// cloud.google.com/go/logging can optionally be used for additional options.


import com.google.cloud.functions.HttpFunction;
import com.google.cloud.functions.HttpRequest;
import com.google.cloud.functions.HttpResponse;
import java.io.BufferedWriter;
import java.io.IOException;
import java.util.logging.Logger;

public class LogHelloWorld implements HttpFunction {

  private static final Logger logger = Logger.getLogger(LogHelloWorld.class.getName());

  public void service(HttpRequest request, HttpResponse response)
      throws IOException {
    System.out.println("I am a log to stdout!");
    System.err.println("I am a log to stderr!");

    logger.info("I am an info log!");
    logger.warning("I am a warning log!");

    BufferedWriter writer = response.getWriter();
    writer.write("Messages successfully logged!");


exports.helloWorld = (req, res) => {
  console.log('I am a log entry!');
  console.error('I am an error!');


use Psr\Http\Message\ServerRequestInterface;

function helloLogging(ServerRequestInterface $request): string
    // Code running in Google Cloud Functions itself writes log entries to
    // Cloud Logging. (Default log severity level is INFO.)
    $log = fopen('php://stderr', 'wb');
    fwrite($log, "Log entry from fwrite().\n");

    // You can also specify a severity level explicitly using structured logs.
    // See this page for a list of log severity values:
    //   https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#LogSeverity
    fwrite($log, json_encode([
      'message' => 'Structured log with error severity',
      'severity' => 'error'
    ]) . PHP_EOL);

    // This doesn't log anything
    error_log('error_log does not log in Cloud Functions!');

    // This will log an error message and immediately terminate the function execution
    // trigger_error('fatal errors are logged!');

    // For HTTP functions, this is added to the HTTP response
    // For CloudEvent functions, this does nothing
    var_dump('var_dump goes to HTTP response for HTTP functions');

    // You can also dump variables using var_export() and forward
    // the resulting string to Cloud Logging via an fwrite() call.
    $entry = var_export('var_export output can be captured.', true);
    fwrite($log, $entry);

    // Functions must return a String or PSR-7 Response object
    return '';


def hello_world(data, context):
    """Background Cloud Function.
         data (dict): The dictionary with data specific to the given event.
         context (google.cloud.functions.Context): The event metadata.
    print('Hello, stdout!')


require "functions_framework"

FunctionsFramework.http "log-helloworld" do |_request|
  # Any output sent to either stdout or stderr will be captured and written to
  # the function's logs.
  puts "Hello, stdout!"
  warn "Hello, stderr!"

  # Return the response body as a string.
  "Hello, world!"

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