PUBLISH to channels in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to publish the message 'Hello' to the channel 'news'.

Redis

PUBLISH [1] Hello

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

Achannel

Bmessage

Cnews

Dhello

Attempts:

3 left

💡 Hint

Common Mistakes

Using the message text as the channel name.

Confusing the channel name with the command.

The PUBLISH command sends a message to a specified channel. Here, the channel name is 'news'.

2fill in blank

medium

Complete the code to publish the message 'Update' to the channel named 'alerts'.

Redis

PUBLISH [1] Update

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

Aupdates

Bnews

Cmessages

Dalerts

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong channel name like 'news' or 'updates'.

Mixing up the message and channel parameters.

The PUBLISH command sends the message 'Update' to the 'alerts' channel.

3fill in blank

hard

Fix the error in the code to correctly publish 'Alert!' to the 'system' channel.

Redis

PUBLISH system [1]

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

A'Alert!'

BAlert

CAlert!

D"Alert!"

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting the message causing syntax errors.

Using double quotes which may not be accepted in some shells.

In Redis CLI, strings with special characters or spaces should be quoted. Here, 'Alert!' needs single quotes.

4fill in blank

hard

Fill both blanks to publish the message 'Server down' to the 'status' channel.

Redis

PUBLISH [1] [2]

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

Astatus

B'Server down'

CServer down

Dserver

Attempts:

3 left

💡 Hint

Common Mistakes

Using unquoted message text with spaces.

Using wrong channel names.

The channel name is 'status' and the message must be quoted as 'Server down' to be valid.

5fill in blank

hard

Fill both blanks to publish the message 'Error 404' to the 'logs' channel using the Redis CLI.

Redis

PUBLISH [1] [2]

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

Alogs

B'Error 404'

CError 404

Derrors

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting the message with spaces.

Using incorrect channel names.

The channel is 'logs' and the message must be quoted as 'Error 404' to handle the space correctly.

Practice

1.

What does the PUBLISH command do in Redis?

easy

A. Stores a message permanently in the database

B. Sends a message to all clients subscribed to a specific channel

C. Deletes all messages from a channel

D. Creates a new channel for clients to subscribe

Solution

1. Step 1: Understand the purpose of PUBLISH

   The PUBLISH command sends messages to clients currently subscribed to a channel.

2. Step 2: Differentiate from storage commands

   PUBLISH does not store messages permanently; it only broadcasts to active subscribers.

3. Final Answer:

   Sends a message to all clients subscribed to a specific channel -> Option B

4. Quick Check:

   PUBLISH broadcasts messages [OK]

Hint: PUBLISH sends messages only to active subscribers [OK]

Common Mistakes:

• Thinking PUBLISH stores messages permanently
• Confusing PUBLISH with channel creation
• Assuming PUBLISH deletes messages

2.

Which of the following is the correct syntax to publish a message 'Hello World' to a channel named news in Redis?

?

easy

A. PUBLISH news 'Hello World'

B. PUBLISH 'Hello World' news

C. PUBLISH news Hello World

D. PUBLISH news, 'Hello World'

Solution

1. Step 1: Recall Redis PUBLISH syntax

   The syntax is: PUBLISH channel message. Quote the message if it contains spaces.

2. Step 2: Identify correct option

   PUBLISH news 'Hello World' matches the syntax exactly.

3. Final Answer:

   PUBLISH news 'Hello World' -> Option A

4. Quick Check:

   Correct Redis PUBLISH syntax = PUBLISH news 'Hello World' [OK]

Hint: Quote messages with spaces: PUBLISH channel 'msg with spaces' [OK]

Common Mistakes:

• Not quoting messages with spaces
• Swapping channel and message order
• Using commas or extra symbols

3.

Given the following Redis commands executed in order:

SUBSCRIBE sports
PUBLISH sports "Game tonight"
PUBLISH news "Weather update"

What messages will the subscriber receive?

medium

A. Only "Game tonight"

B. Both "Game tonight" and "Weather update"

C. Only "Weather update"

D. No messages

Solution

1. Step 1: Identify subscribed channel

   The subscriber is subscribed to the 'sports' channel only.

2. Step 2: Check published messages

   Messages published to 'sports' are received; messages to 'news' are ignored by this subscriber.

3. Final Answer:

   Only "Game tonight" -> Option A

4. Quick Check:

   Subscribers get messages only from their channels [OK]

Hint: Subscribers get messages only from their subscribed channels [OK]

Common Mistakes:

• Assuming subscriber gets all published messages
• Confusing channel names
• Ignoring subscription context

4.

What is wrong with this Redis command to publish a message?

PUBLISH

Choose the best explanation.

medium

A. PUBLISH cannot be used without SUBSCRIBE

B. Channel name is invalid

C. Message is too long

D. Missing channel and message arguments

Solution

1. Step 1: Check required arguments for PUBLISH

   PUBLISH requires two arguments: channel and message.

2. Step 2: Identify missing parts in the command

   The command only has PUBLISH with no arguments, so it is incomplete.

3. Final Answer:

   Missing channel and message arguments -> Option D

4. Quick Check:

   PUBLISH needs channel and message [OK]

Hint: PUBLISH needs channel and message arguments [OK]

Common Mistakes:

• Thinking PUBLISH works without arguments
• Assuming message length causes error here
• Believing SUBSCRIBE is required before PUBLISH

5.

You want to send a notification to multiple channels news and alerts at once. Which Redis approach is best?

hard

A. Create a new channel combining both names and publish once

B. Publish to one channel and expect all subscribers to receive it

C. Use multiple PUBLISH commands, one per channel

D. Use a Redis command to publish to multiple channels simultaneously

Solution

1. Step 1: Understand Redis PUBLISH limitations

   Redis PUBLISH sends messages to one channel at a time; no built-in multi-channel publish exists.

2. Step 2: Choose correct method to notify multiple channels

   Send separate PUBLISH commands for each channel to reach all subscribers.

3. Final Answer:

   Use multiple PUBLISH commands, one per channel -> Option C

4. Quick Check:

   Multiple channels need multiple PUBLISH calls [OK]

Hint: Publish separately to each channel for multiple notifications [OK]

Common Mistakes:

• Expecting one PUBLISH to reach multiple channels
• Combining channel names incorrectly
• Assuming Redis supports multi-channel publish natively