Sort Docker Containers with Bash Function: A Simple Guide

Docker has become an indispensable tool for developers and system administrators, offering a seamless way to package, distribute, and run applications in isolated environments. However, as the number of containers grows, managing them efficiently becomes a challenge. Sorting Docker containers based on specific criteria—such as status, creation time, or resource usage—can significantly streamline your workflow. In this guide, we’ll explore how to create a simple Bash function to sort Docker containers, making it easier to monitor and manage your environment.

Why Sort Docker Containers?

Before diving into the technical details, let’s understand why sorting Docker containers is beneficial. By organizing containers, you can:

1. Quickly Identify Running or Stopped Containers: Prioritize active containers for monitoring or troubleshooting.
2. Optimize Resource Allocation: Sort by CPU or memory usage to identify resource-intensive containers.
3. Track Container Lifecycles: Sort by creation time to understand which containers are the oldest or newest.
4. Enhance CLI Workflow: Automate repetitive tasks and improve productivity.

Prerequisites

To follow along, ensure you have:

• Docker installed and running on your system.
• Basic familiarity with Bash scripting and Docker CLI commands.

Step 1: Understanding Docker CLI Output

The docker ps command lists running containers, while docker ps -a includes all containers (running and stopped). The output includes columns like CONTAINER ID, IMAGE, COMMAND, CREATED, STATUS, PORTS, and NAMES. We’ll use this output as the basis for sorting.

$ docker ps -a
CONTAINER ID   IMAGE          COMMAND                  CREATED         STATUS                        PORTS     NAMES
8a2d3c4b6e7f   nginx          "/docker-entrypoint.…"   5 minutes ago   Up 5 minutes                  80/tcp    web_server
1b3c4d5e6f7g   alpine         "sleep 1000"             10 minutes ago  Exited (0) 9 minutes ago                  sleepy_container

Step 2: Creating the Bash Function

We’ll create a Bash function called sort_docker_containers that accepts a sorting criterion (e.g., status, created, name) and sorts the containers accordingly.

#!/bin/bash

sort_docker_containers() {
    local criterion="$1"
    local headers=$(docker ps -a --format "table {{.ID}}\t{{.Image}}\t{{.Command}}\t{{.CreatedAt}}\t{{.Status}}\t{{.Ports}}\t{{.Names}}" | head -n 1)
    local containers=$(docker ps -a --format "table {{.ID}}\t{{.Image}}\t{{.Command}}\t{{.CreatedAt}}\t{{.Status}}\t{{.Ports}}\t{{.Names}}" | tail -n +2)

    case "$criterion" in
        status)
            echo "$headers"
            echo "$containers" | sort -k 5
            ;;
        created)
            echo "$headers"
            echo "$containers" | sort -k 4
            ;;
        name)
            echo "$headers"
            echo "$containers" | sort -k 7
            ;;
        *)
            echo "Usage: sort_docker_containers [status|created|name]"
            ;;
    esac
}

Step 3: Breaking Down the Function

Let’s dissect the function to understand its components:

1. Headers and Containers Extraction:

   • headers: Captures the header row of the docker ps -a output.
   • containers: Captures the container data rows, excluding the header.

2. Sorting Logic:

   • The case statement handles different sorting criteria:
     • status: Sorts by the STATUS column (5th column).
     • created: Sorts by the CREATED column (4th column).
     • name: Sorts by the NAMES column (7th column).

3. Output:

   • The sorted output is displayed with the headers intact.

Step 4: Using the Function

Save the function to a file, e.g., docker_sort.sh, and source it in your terminal:

source docker_sort.sh

Now, you can use the function to sort containers:

$ sort_docker_containers status
CONTAINER ID   IMAGE          COMMAND                  CREATED             STATUS                        PORTS     NAMES
1b3c4d5e6f7g   alpine         "sleep 1000"             10 minutes ago      Exited (0) 9 minutes ago                  sleepy_container
8a2d3c4b6e7f   nginx          "/docker-entrypoint.…"   5 minutes ago       Up 5 minutes                  80/tcp    web_server

Advanced Enhancements

To make the function more robust, consider these improvements:

1. Custom Formatting: Use docker ps -a --format to customize the output columns.
2. Resource Sorting: Add sorting by CPU or memory usage using docker stats.
3. Interactive Menu: Create a menu-driven interface for easier selection of sorting criteria.

FAQ Section

Conclusion

Sorting Docker containers with a Bash function is a simple yet powerful way to enhance your container management workflow. By customizing the sorting criteria, you can tailor the function to your specific needs. Whether you’re a developer, DevOps engineer, or system administrator, this tool will save you time and improve your productivity. Start implementing it today and take control of your Docker environment!