Docker has a host of instruction commands. These are commands that are put in the Docker File. Let’s look at the ones which are available.
CMD Instruction
To execute a command at runtime use by this command when execute by the container.
Syntax
CMD command param1
Options
- command − This is the Command to run when launch by the container.
- param1 − The Command enter in to the parameter by this.
Return Value
The command will execute accordingly.
Example
In our example, we will enter a simple Hello World echo in our Docker File and create an image and launch a container from it.
Step1 − Build the Docker File with the following commands −
FROM ubuntu MAINTAINER demousr@gmail.com CMD [“echo” , “hello world”]
Here, Hello World just use to print by the CMD.
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Step2 − Build the image using the Docker build command.
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Step3 − Run a container from the image.
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ENTRYPOINT
This command can also be used to execute commands at runtime for the container. But we can be more flexible with the ENTRYPOINT command.
Syntax
ENTRYPOINT command param1
Options
- command − This is the Command to run when launch by the container.
- param1 − The Command enter in to the parameter by this.
Return Value
The command will execute accordingly.
Example
Let’s take a look at an example to understand more about ENTRYPOINT. In our example, we will enter a simple echo command in our Docker File and create an image and launch a container from it.
Step1 − Build the Docker File with the following commands −
FROM ubuntu MAINTAINER demousr@gmail.com ENTRYPOINT [“echo”]
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Step2 − Build the image using the Docker build command.
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Step3 − Run a container from the image.
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ENV
The Container uses to set environment variables by this command.
Syntax
ENV key value
Options
- Key − This is the key for the environment variable.
- value − This is the value for the environment variable.
Return Value
The command will execute accordingly.
Example
In our example, we will enter a simple echo command in our Docker File and create an image and launch a container from it.
Step1 − Build the Docker File with the following commands −
FROM ubuntu MAINTAINER demousr@gmail.com ENV var1=Tutorial var2=point
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Step2 − Build the image using the Docker build command.
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Step3 − Run a container from the image.
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Step4 − Finally, execute the env command to see the environment variables.
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WORKDIR
The Container uses to set the working directory by this command.
Syntax
WORKDIR dirname
Options
- dirname − The new working directory. If the directory does not exist, it will be added.
Return Value
The command will execute accordingly.
Example
In our example, we will enter a simple echo command in our Docker File and create an image and launch a container from it.
Step1 − Build the Docker File with the following commands −
FROM ubuntu MAINTAINER demousr@gmail.com WORKDIR /newtemp CMD pwd
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Step2 − Build the image using the Docker build command.
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Step3 − Run a container from the image.
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In This guide, we learned about Docker instruction commands. To know more click here.
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