---
title: Create, Write to, and Read from a Log File
slug: litmusedge/how-to-guides/flows-guides/create-write-to-and-read-from-a-log-file
description: You can use Flows to create a log file on the Litmus Edge device, populate it, and read its contents. 
docTags: 
createdAt: 2023-06-07T19:07:30.000Z
---

You can use Flows to create a log file on the Litmus Edge device, populate it, and read its contents. 

:::hint{type="info"}
**Note: **File names used in node configurations are case sensitive.
:::

# Create a Log File

Before any data can be written, you need to create create a file first.

**To create a file in a flow:**

1. In Litmus Edge, navigate to the **Flows Manager **and create a new flow. 
   See [Create a Flow](docId\:wh4ZihWF0PwMRYRbAZbco) to learn more. 
2. Drag a **write file** node and an **inject **node to the canvas and wire them together.
   ![](https://api.archbee.com/api/optimize/SSUUxKZUk9bFTEPNn_6Zo/DUnpLEQg8JpkbWXkvSTEU_image.png "Flows canvas with write file node")
3. Double-click the **write** **file** node.
   The *Edit write file *node dialog box appears.
   - **Filename:** Enter a **filename **prefaced with a forward slash ( `/` ). 
     - The forward slash is required in the filename.
       Example: `/ftp-data/testlogfile.log`
     - The file is created on the Litmus Edge device.
     - If a subdirectory already exists, you can supply the full path to the file.
       Example: `/ftp-data/testlogfile` or `/logfiles/testlogfile`.
   - **Action:** Select **append to file** from the drop-down menu and click **Done**.
     ::Image[]{src="https://api.archbee.com/api/optimize/SSUUxKZUk9bFTEPNn_6Zo/RJ7EBYF7NHe1EnyUzQuWQ_image.png" size="70" width="508" height="477" position="center" caption="Edit write file node dialog box" showCaption="true"}
4. Click **Deploy **to save the flow. 
5. Click the button on the left side of the **inject **(timestamp) node to inject the current timestamp into the **write file** node, which creates the file locally if it does not already exist. 
   In this example, the `/ftp-data/testlogfile.log` file is saved.

# Read a File

You can use a **Read file **node to access a file that you have created or written to.

**To read a file: **

1. From the Flows canvas, drag a **read file** node, **inject **node, and **debug **node to the canvas and wire them together.
   ![](https://api.archbee.com/api/optimize/SSUUxKZUk9bFTEPNn_6Zo/I3RXPC_Qezq9u1ppGCYy0_image.png "Flows canvas with read file node")
2. Double-click the **read file **node.
   The* Edit read file node *dialog box appears.
   - **Filename:** Enter the **filename **prefaced with a forward slash ( `/` ). 
     A forward slash is required to be the first character of the filename.
     Example: `/ftp-data/testlogfile.log`
   - **Output:** From the drop-down menu, select the standard **single utf8 string **format.
   - Click **Done.**
     ::Image[]{src="https://api.archbee.com/api/optimize/SSUUxKZUk9bFTEPNn_6Zo/m7gvFU9YU7LiUWBXNeUs8_image.png" size="70" width="503" height="405" position="center" caption="Edit read file node dialog box" showCaption="true"}
3. Click **Deploy.**
4. Drag the **Sidebar **up from the bottom of the canvas and select the **Debug** icon.
   ![](https://api.archbee.com/api/optimize/SSUUxKZUk9bFTEPNn_6Zo/NR-2HuY85vCMwwDX8RM7y_image.png "Debug icon on flows canvas")
5. Click the **inject **node button to trigger the flow.
   The debug area shows the timestamp that has been written to the `/ftp-data/testlogfile.log` file.
   ![](https://api.archbee.com/api/optimize/SSUUxKZUk9bFTEPNn_6Zo/N6VKJpRNTt4o11ntJuFpU_image.png "Output of reading a file")

# Write to a Pre-Existing File

In the Create a Log File steps, the inject node triggered file creation. The following steps show how to write to an existing file.

**To continue writing to the file that was created in **[Create a Log File](docId\:QT1zCMl1_hfu1YJHqjHnw)**:**

1. From the Flows canvas, double-click the **write file** node.
   The *Edit write file *node dialog box appears.
   - **Filename:** Enter a **filename **prefaced with a forward slash ( `/` ). 
     We use the same file we created before: `/ftp-data/testlogfile.log`
   - **Action:** Select **append to file** from the drop-down menu.
   - Click **Done**.
     ::Image[]{src="https://api.archbee.com/api/optimize/SSUUxKZUk9bFTEPNn_6Zo/UdiLRuIatRa6nZjvIiV3O_image.png" size="70" width="510" height="488" position="center" caption="Edit write file node dialog box" showCaption="true"}
2. Click **Deploy.**
3. Click the **inject **node button to inject the current timestamp into the **write file **node, which appends the output to the pre-existing file.
4. Drag the **Sidebar **up from the bottom of the canvas and select the **Debug **icon.
   ![](https://api.archbee.com/api/optimize/SSUUxKZUk9bFTEPNn_6Zo/t5B0Bbra-BOIsEySwdOjl_image.png "Debug icon on flows canvas")
5. Click the **inject **node button from the *read file* node configuration to verify that the write task to the pre-existing file was successful.
   ![](https://api.archbee.com/api/optimize/SSUUxKZUk9bFTEPNn_6Zo/bF9Hx9_Tz-cgijJJF_Zvb_image.png "Output of reading a file")

# Write a Message to a File

You can inject a string message into a pre-existing or a new file from the Flows.

**To write a message (text string) to a file:**

1. In your Flow canvas, double-click the **inject** node.
   The *Edit inject node* dialog box appears.
   - **msg.payload:** From the drop-down menu, select **String**.
   - Enter text of your choice in the blank text field.
     In this example, we have entered: `Hello World`.
   - Click **Done**.
     ::Image[]{src="https://api.archbee.com/api/optimize/SSUUxKZUk9bFTEPNn_6Zo/F0bgpuXGMXR2_HpNnKz3Z_image.png" size="70" width="572" height="333" position="center" caption="Edit inject node dialog box " showCaption="true"}
2. Click **Deploy**.
3. Click the **inject **node button to inject the message into the **write file **node, which appends the output to the pre-existing file.
4. Drag the **Sidebar **up from the bottom of the canvas and select the **Debug **icon.
   ![](https://api.archbee.com/api/optimize/SSUUxKZUk9bFTEPNn_6Zo/t5B0Bbra-BOIsEySwdOjl_image.png "Debug icon on flows canvas")
5. Click the **inject **node button from the *read file* node configuration to verify that the message was written to the file.
   ![](https://api.archbee.com/api/optimize/SSUUxKZUk9bFTEPNn_6Zo/ba3EJG8wXOXut7FQSS6bG_image.png "Output of reading a file")