How To Comment In Dockerfile?

The purpose of comments in a Dockerfile is to both clarify and improve the readability of the instructions. It can also be used to stop execution when testing other code. The comments are meant to serve as a source of code line information. Comments are a frequent way for programmers to document their work.

Why are comments used in the Dockerfile?

Comments in a Dockerfile are used to summarize a Dockerfile, identify a file purpose, or clarify an instruction segment that appears unclear. Comments are also used for:

• Summarize the purpose of the Dockerfile, making it clear what the built image will contain and its intended use.
• Clarify complex or non-obvious Dockerfile instructions, which is especially useful for intricate installations or configurations.
• Comments make Dockerfiles easier to read and understand, especially for new developers.

Types of Dockerfile Comments

In Dockerfile, only one type of commenting is available, which is “Single Line Comment.” For multiple lines, multiple “#” characters need to be used at the beginning of the instructions.

Comments for the Dockerfile can be used by starting the line with a ‘#’ character. The Docker Daemon ignores these lines starting with ‘#” and executes the rest of the file.

Syntax :

# Single-line comment

or for multiple lines:

# First comment
# Second comment

Example:

# Use a Python base image
FROM python:3.10

# Set the working directory in the container
WORKDIR /app

# Copy the requirements file
COPY requirements.txt .

Note: Although the code in this instance displays as a Matlab file, it has nothing to do with Matlab. Instead, it represents the content of a Dockerfile.

Tip: Some IDEs provide shortcut to apply comments as well, the shortcut to make a single line into a comment is ‘ctrl + /’.

Comments are an essential component of programming, whether they are written for ourselves or for other team members who may visit the code later. It is a useful tool in a variety of scenarios and aids in the explanation of how the code functions. Here, comments might be helpful in providing vital details about the Dockerfile, such as how to run the file.

How Docker Daemon process Comments ?

Whenever Docker Daemon Processes the Dockerfile for given project, it executes the instructions line by line, interpreting and executing the instructions it contains to create the layers that make up the image. Comments in dockefile start with “#” , and lines starting with “#” are completely ignored by the Docker daemon. It does not process or executes them in any way.

To learn more about Docker and Dockerfiles visit our Docker Tutorial.

Comment in dockerfile – FAQ’s

How do I comment on Dockerfile?

To comment in a Dockerfile, use the # symbol. Comments can be added at the beginning of a line or after an instruction to provide explanations or context within the Dockerfile.

How to comment multiple lines in Dockerfile?

In a Dockerfile, you can comment multiple lines by using the # symbol at the beginning of each line, or you can use the \ character at the end of each line to continue the comment to the next line.