# Applying a path pattern when filtering in Eventarc

Author: [Mete Atamel](https://atamel.dev/) | Published: 2022-03-02 | Updated: 2023-01-10 | Topics: Eventarc, Serverless, Google Cloud Platform, How To | Canonical: https://atamel.dev/posts/2022/03-02_path_patterns_eventarc/


![Eventarc](/img/2022/Eventarc-128-color.png)

You can now apply a [path
pattern](https://cloud.google.com/eventarc/docs/path-patterns) when filtering in
Eventarc. This is especially useful when you need to filter on [resource
names](https://cloud.google.com/apis/design/resource_names) beyond exact match.
Path pattern syntax allows you to define a regex-like expression that matches
events as broadly as you like.

Let's take a look at a concrete example.

## Without path patterns

Let's say you want to listen for new file creations in a Cloud Storage bucket
with an AuditLog trigger.

*Note: The right way of listening for Cloud Storage events is to use a Cloud
Storage trigger. I'm using the AuditLog trigger here to illustrate the path
patterns, so please bear with me.*

This is how you'd create the Audit Log trigger before:

```sh
gcloud eventarc triggers create $TRIGGER_NAME\
  --destination-run-service=$SERVICE_NAME \
  --destination-run-region=$REGION \
  --event-filters="type=google.cloud.audit.log.v1.written" \
  --event-filters="serviceName=storage.googleapis.com" \
  --event-filters="methodName=storage.objects.create" \
  --service-account=$PROJECT_NUMBER-compute@developer.gserviceaccount.com
```

The trigger above would match events from **all** buckets, as you're not
filtering on a specific resource (i.e. bucket). You have to filter for the right
bucket in the code of the service that receives the event, not ideal.

You could try to add the resource name as a filter but the resource here is the
actual file name with the full path. Your trigger needs to look like this to
match creation of `file1.txt` in `bucket1`:

```sh
gcloud eventarc triggers create $TRIGGER_NAME\
  --destination-run-service=$SERVICE_NAME \
  --destination-run-region=$REGION \
  --event-filters="type=google.cloud.audit.log.v1.written" \
  --event-filters="serviceName=storage.googleapis.com" \
  --event-filters="methodName=storage.objects.create" \
  --event-filters="resourceName=/projects/_/buckets/bucket-1/objects/file1.txt" \
  --service-account=$PROJECT_NUMBER-compute@developer.gserviceaccount.com
```

But the problem is: You probably don't know the names of created files ahead of
time.

## With path patterns

Fast forward to path patterns today. Now, you can create a trigger with a
pattern for the resource name as follows:

```sh
gcloud eventarc triggers create $TRIGGER_NAME\
  --destination-run-service=$SERVICE_NAME \
  --destination-run-region=$REGION \
  --event-filters="type=google.cloud.audit.log.v1.written" \
  --event-filters="serviceName=storage.googleapis.com" \
  --event-filters="methodName=storage.objects.create" \
  --event-filters-path-pattern="resourceName=/projects/_/buckets/bucket-1/objects/*" \
  --service-account=$PROJECT_NUMBER-compute@developer.gserviceaccount.com
```

This trigger will filter for all file creations within the bucket. This is
exactly what you want when you're listening for new file creation events.

## Valid Patterns

Here are some valid patterns from the documentation:

| Pattern      | Description |
| -----------  | ----------- |
| /projects/_/buckets/bucket-1/objects/file1.txt | Specific resource name.|
| /projects/_/buckets/bucket-1/objects/* | Matches any file in the objects directory.|
| /projects/_/buckets/bucket-1/objects/*.txt | Matches all TXT files in the objects directory.|
| /projects/_/buckets/bucket-1/objects/file-*.txt | Matches all TXT files with prefix file- in the objects directory.|
| /projects/_/**/file-*.txt | Matches any TXT file with prefix file- for all buckets.|
| /projects/_/buckets/bucket-\*/objects/file-\*.txt | Matches all TXT files with prefix file- for any bucket with prefix bucket-.|

If you want to learn more, check out the [Understand path
patterns](https://cloud.google.com/eventarc/docs/path-patterns) docs page.

You can also check out the AuditLog step of [Trigger Cloud Run with events from
Eventarc](https://codelabs.developers.google.com/codelabs/cloud-run-events?hl=en#9)
codelab for an example on how to use path patterns.

---

Feel free to reach out to me on Twitter [@meteatamel](https://twitter.com/meteatamel)
for any questions/feedback.