Combining RUN commands in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the Dockerfile line to combine two commands in one RUN instruction using the correct operator.

Docker

RUN apt-get update [1] apt-get install -y curl

Drag options to blanks, or click blank then click option'

A||

B|

C;

D&&

Attempts:

3 left

💡 Hint

Common Mistakes

Using ';' runs commands regardless of success.

Using '|' pipes output, not for chaining commands.

Using && ensures the second command runs only if the first succeeds, which is best practice in Dockerfiles.

2fill in blank

medium

Complete the Dockerfile RUN command to update packages and clean cache in one line.

Docker

RUN apt-get update [1] apt-get upgrade -y [2] apt-get clean

Drag options to blanks, or click blank then click option'

A&&

B;

C||

D|

Attempts:

3 left

💡 Hint

Common Mistakes

Using ';' runs commands regardless of success.

Using '||' runs next command only if previous fails.

Using && between commands ensures each runs only if the previous succeeds, which is safer for Docker builds.

3fill in blank

hard

Fix the error in this Dockerfile RUN command by choosing the correct operator to combine commands.

Docker

RUN mkdir /app [1] cd /app [2] git clone https://repo.url

Drag options to blanks, or click blank then click option'

A&&

B;

C|

D||

Attempts:

3 left

💡 Hint

Common Mistakes

Using ';' runs commands regardless of success.

Using '|' pipes output, not for chaining commands.

Using && ensures each command runs only if the previous one succeeds, preventing errors in the build.

4fill in blank

hard

Fill both blanks to combine commands that update, install, and clean in one RUN instruction.

Docker

RUN apt-get update [1] apt-get install -y nginx [2] apt-get clean

Drag options to blanks, or click blank then click option'

A&&

B;

C||

D|

Attempts:

3 left

💡 Hint

Common Mistakes

Using ';' runs commands regardless of success.

Using '||' runs next command only if previous fails.

Using && between commands ensures each runs only if the previous succeeds, which is best practice.

5fill in blank

hard

Fill all three blanks to create a RUN command that updates, installs curl, and cleans cache safely.

Docker

RUN apt-get update [1] apt-get install -y [2] [3] apt-get clean

Drag options to blanks, or click blank then click option'

A&&

Bcurl

D;

Attempts:

3 left

💡 Hint

Common Mistakes

Using ';' instead of '&&' breaks safe chaining.

Missing the package name causes install failure.

Use && to chain commands safely and specify curl as the package to install.

Practice

1. Why is it recommended to combine multiple commands in a single RUN instruction in a Dockerfile?

easy

A. To make the Dockerfile longer and more complex

B. To run commands in parallel for faster builds

C. To reduce the number of image layers and keep the image size smaller

D. To avoid using the shell in Dockerfile commands

Solution

1. Step 1: Understand Docker image layers

   Each RUN instruction creates a new image layer, increasing image size.

2. Step 2: Combine commands to reduce layers

   Combining commands with && in one RUN reduces layers and image size.

3. Final Answer:

   To reduce the number of image layers and keep the image size smaller -> Option C

4. Quick Check:

   Combining RUN commands = fewer layers [OK]

Hint: Combine commands with && to reduce image layers [OK]

Common Mistakes:

• Thinking combining commands makes builds faster
• Believing each command runs in parallel
• Ignoring image size impact of multiple RUNs

2. Which of the following is the correct syntax to combine two commands in a single RUN instruction in a Dockerfile?

easy

A. RUN apt-get update && apt-get install -y curl

B. RUN apt-get update; apt-get install -y curl

C. RUN apt-get update | apt-get install -y curl

D. RUN apt-get update &&& apt-get install -y curl

Solution

1. Step 1: Identify correct command chaining operator

   The && operator chains commands so the second runs only if the first succeeds.

2. Step 2: Check each option's syntax

   RUN apt-get update && apt-get install -y curl uses && correctly; others use invalid or unsafe separators.

3. Final Answer:

   RUN apt-get update && apt-get install -y curl -> Option A

4. Quick Check:

   Use && to chain commands safely [OK]

Hint: Use && to chain commands safely in RUN [OK]

Common Mistakes:

• Using semicolon without error checking
• Using invalid operators like | or &&&
• Not chaining commands properly causing build errors

3. What will be the result of this Dockerfile snippet?

RUN apt-get update && apt-get install -y curl && rm -rf /var/lib/apt/lists/*

medium

A. Creates three separate layers for each command

B. Only updates package lists and installs curl, but does not clean files

C. Fails because rm command is invalid in RUN

D. Updates package lists, installs curl, and cleans temporary files in one layer

Solution

1. Step 1: Analyze the chained RUN commands

   The commands update packages, install curl, then remove apt cache files in one RUN.

2. Step 2: Understand layer creation

   All commands combined in one RUN create a single image layer with all changes.

3. Final Answer:

   Updates package lists, installs curl, and cleans temporary files in one layer -> Option D

4. Quick Check:

   Combined RUN commands = single layer with all steps [OK]

Hint: One RUN with && creates one layer with all commands [OK]

Common Mistakes:

• Thinking each command creates a separate layer
• Assuming rm command is invalid in RUN
• Ignoring cleaning temporary files effect

4. You wrote this Dockerfile line:

RUN apt-get update & apt-get install -y git

What is the problem with this command?

medium

A. The & operator is correct and recommended for RUN commands

B. The single & runs commands in background, causing build errors

C. The commands will run sequentially without errors

D. The command will install git twice

Solution

1. Step 1: Understand the & operator in shell

   Single & runs the first command in background, not waiting for completion.

2. Step 2: Impact on Docker build

   This causes the second command to run immediately, possibly before update finishes, leading to errors.

3. Final Answer:

   The single & runs commands in background, causing build errors -> Option B

4. Quick Check:

   Use && not & to chain RUN commands [OK]

Hint: Use &&, not &, to chain commands in RUN [OK]

Common Mistakes:

• Using & instead of && for chaining
• Assuming commands run sequentially with &
• Ignoring build errors caused by background commands

5. You want to install curl and git in one RUN command and clean up apt cache to keep the image small. Which Dockerfile line correctly does this?

hard

A. RUN apt-get update && apt-get install -y curl git && rm -rf /var/lib/apt/lists/*

B. RUN apt-get update; apt-get install -y curl git; rm -rf /var/lib/apt/lists/*

C. RUN apt-get update && apt-get install -y curl && apt-get install -y git && rm -rf /var/lib/apt/lists/*

D. RUN apt-get update & apt-get install -y curl git && rm -rf /var/lib/apt/lists/*

Solution

1. Step 1: Combine update and install commands safely

   Use && to chain update and install commands to ensure sequential success.

2. Step 2: Clean apt cache in the same RUN

   Remove temporary files with rm -rf /var/lib/apt/lists/* in the same RUN to keep image small.

3. Step 3: Check options for correctness

   RUN apt-get update && apt-get install -y curl git && rm -rf /var/lib/apt/lists/* chains all commands correctly in one RUN; others use semicolons or background & causing issues or inefficiencies.

4. Final Answer:

   RUN apt-get update && apt-get install -y curl git && rm -rf /var/lib/apt/lists/* -> Option A

5. Quick Check:

   Chain with && and clean in one RUN [OK]

Hint: Chain update, install, and cleanup with && in one RUN [OK]

Common Mistakes:

• Using semicolons instead of && without error checking
• Running install commands separately (inefficient)
• Using & causing background execution errors