rosservice command-line tools - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the rosservice command-line tool in ROS?

The rosservice tool lets you interact with ROS services from the command line. You can list, call, and get information about services running in your ROS system.

beginner

How do you list all available ROS services using rosservice?

Use the command rosservice list to see all active services in your ROS environment.

beginner

What does the command rosservice call /service_name args do?

It calls the service named /service_name with the given arguments args. This sends a request to the service and waits for the response.

intermediate

How can you find the type of a ROS service using rosservice?

Use rosservice type /service_name to get the service type, which tells you the message format the service uses.

intermediate

What command shows detailed information about a specific ROS service?

The command rosservice info /service_name displays details like the service provider node and service type.

Which command lists all active ROS services?

A rosservice list

B rosservice call

C rosservice info

D rosservice type

The rosservice list command shows all active services.

What does rosservice call /my_service do?

A Calls the service named /my_service

B Lists all services

C Shows service type

D Displays service info

It calls the service named /my_service with optional arguments.

How do you find the message type of a service?

A rosservice list

B rosservice call

C rosservice type

D rosservice info

The rosservice type command shows the service message type.

Which command shows the node providing a service?

A rosservice list

B rosservice info

C rosservice call

D rosservice type

The rosservice info command shows the provider node and other details.

If you want to call a service with arguments, which command do you use?

A rosservice list

B rosservice type

C rosservice info

D rosservice call /service_name args

Use rosservice call /service_name args to send arguments to the service.

Explain how to use rosservice to find and call a service in ROS.

Think about the steps from discovering to using a service.

Describe the information you get from rosservice info /service_name and why it is useful.

Consider what details help you understand a service's role.

Practice

1. What does the rosservice list command do in ROS?

easy

A. It shows all available services currently running in the ROS system.

B. It starts a new ROS service.

C. It deletes a specified ROS service.

D. It shows the status of ROS nodes.

Solution

1. Step 1: Understand the purpose of rosservice list

   This command is designed to display all active services in the ROS environment.

2. Step 2: Compare with other options

   Starting or deleting services and showing node status are done by other commands, not rosservice list.

3. Final Answer:

   It shows all available services currently running in the ROS system. -> Option A

4. Quick Check:

   List services = rosservice list [OK]

Hint: Remember: 'list' always shows all current services [OK]

Common Mistakes:

• Confusing service listing with node status
• Thinking it starts or deletes services
• Mixing up with rosnode commands

2. Which of the following is the correct syntax to call a ROS service named /add_two_ints with arguments a=2 and b=3 using rosservice?

easy

A. rosservice call /add_two_ints 2 3

B. rosservice call /add_two_ints {a: 2, b: 3}

C. rosservice call /add_two_ints --a 2 --b 3

D. rosservice call /add_two_ints a:=2 b:=3

Solution

1. Step 1: Recall rosservice call argument format

   Named arguments like a=2 and b=3 are passed using YAML dictionary syntax {a: 2, b: 3}.

2. Step 2: Check each option

   rosservice call /add_two_ints {a: 2, b: 3} uses the correct YAML format specifying arguments by name. A is positional (no names), B uses invalid flags, D uses unsupported :=.

3. Final Answer:

   rosservice call /add_two_ints {a: 2, b: 3} -> Option B

4. Quick Check:

   YAML {name: value} for named args [OK]

Hint: Use YAML '{name: value}' for named service arguments [OK]

Common Mistakes:

• Using positional args without naming a and b
• Using invalid flags like --a
• Using := instead of : in YAML

3. What will be the output of the command rosservice type /clear if the service /clear exists and is of type std_srvs/Empty?

medium

A. Error: Service type unknown

B. /clear is not a valid service

C. Service /clear has no type

D. std_srvs/Empty

Solution

1. Step 1: Understand rosservice type command

   This command returns the type of the specified service if it exists.

2. Step 2: Given service /clear exists and is std_srvs/Empty

   The command will output exactly the service type string.

3. Final Answer:

   std_srvs/Empty -> Option D

4. Quick Check:

   rosservice type returns service type string [OK]

Hint: rosservice type shows the service's message type [OK]

Common Mistakes:

• Assuming it shows service status instead of type
• Thinking it returns an error if service exists
• Confusing with rosnode commands

4. You run rosservice call /add_two_ints a:=5 b:=7 but get an error: ERROR: Service [/add_two_ints] not available. What is the most likely cause?

medium

A. The service /add_two_ints is not currently running or advertised.

B. The arguments a and b are incorrectly formatted.

C. The ROS master is not running.

D. The service /add_two_ints does not accept integer arguments.

Solution

1. Step 1: Analyze the error message

   The error says the service is not available, meaning it is not running or advertised.

2. Step 2: Check other options

   Argument format errors cause different errors; ROS master not running causes broader failures; service argument types mismatch cause different errors.

3. Final Answer:

   The service /add_two_ints is not currently running or advertised. -> Option A

4. Quick Check:

   Service not available means not running [OK]

Hint: Service not available means it's not running or advertised [OK]

Common Mistakes:

• Assuming argument format is wrong from this error
• Not checking if ROS master is running
• Thinking service argument types cause this error

5. You want to check the detailed request and response format of a service named /compute_path. Which command should you use to see the service definition?

hard

A. rosservice info /compute_path

B. rosservice type /compute_path

C. rosservice show /compute_path

D. rosservice find /compute_path

Solution

1. Step 1: Understand commands for service details

   rosservice show displays the full request and response message format of a service.

2. Step 2: Compare with other commands

   rosservice info shows service provider info, rosservice type shows only the type name, and rosservice find searches for services by type.

3. Final Answer:

   rosservice show /compute_path -> Option C

4. Quick Check:

   Use rosservice show to see request/response format [OK]

Hint: Use rosservice show to view full service message format [OK]

Common Mistakes:

• Using rosservice info expecting message format
• Confusing rosservice type with detailed format
• Trying rosservice find which searches by type