rosservice command-line tools - Step-by-Step Execution

Concept Flow - rosservice command-line tools

Start: User runs rosservice command

↓

Parse command and arguments

↓

Check command type: list, call, find, type, etc.

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List services

↓

Display output or error message

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End

The rosservice command-line tool starts by parsing the user's input, then runs the requested command like listing services or calling one, and finally shows the result or error.

Execution Sample

ROS

rosservice list
rosservice type /add_two_ints
rosservice call /add_two_ints "a: 2\nb: 3"

These commands list all services, show the type of a service, and call a service with parameters.

Execution Table

Step	Command	Action	Result/Output
1	rosservice list	Parse command 'list'	Retrieve all active service names
2	rosservice list	Display list	/add_two_ints /clear_costmap /get_map
3	rosservice type /add_two_ints	Parse command 'type' with service '/add_two_ints'	Find service type
4	rosservice type /add_two_ints	Display type	example_interfaces/AddTwoInts
5	rosservice call /add_two_ints "a: 2\nb: 3"	Parse command 'call' with service and parameters	Send request to service
6	rosservice call /add_two_ints "a: 2\nb: 3"	Receive response	sum: 5
7	rosservice call /unknown_service	Parse command 'call' with unknown service	Error: Service not found
8	rosservice list	Parse command 'list'	Retrieve all active service names
9	rosservice list	Display list	/add_two_ints /clear_costmap /get_map
10	End	No more commands	Process ends

💡 User finishes commands or encounters error; rosservice tool exits.

Variable Tracker

Variable	Start	After 1	After 3	After 5	After 7	Final
command	None	list	type /add_two_ints	call /add_two_ints with params	call /unknown_service	list
service_list	Empty	/add_two_ints, /clear_costmap, /get_map	/add_two_ints, /clear_costmap, /get_map	/add_two_ints, /clear_costmap, /get_map	/add_two_ints, /clear_costmap, /get_map	/add_two_ints, /clear_costmap, /get_map
service_type	None	None	example_interfaces/AddTwoInts	example_interfaces/AddTwoInts	None	example_interfaces/AddTwoInts
call_response	None	None	None	sum: 5	Error: Service not found	sum: 5

Key Moments - 3 Insights

Why does rosservice call fail with 'Service not found'?

If the service name is not in the active service list (see execution_table step 7), rosservice cannot call it and shows an error.

What does rosservice list show?

It shows all currently active services available to call, as seen in execution_table steps 2 and 9.

How does rosservice call use parameters?

Parameters are passed as YAML-like strings (step 5), which rosservice sends to the service and waits for a response.

Visual Quiz - 3 Questions

Look at the execution table, what is the output of 'rosservice type /add_two_ints' at step 4?

A sum: 5

B /add_two_ints

C example_interfaces/AddTwoInts

D Service not found

💡 Hint

Check the 'Result/Output' column at step 4 in the execution_table.

At which step does rosservice call return an error due to unknown service?

A Step 7

B Step 5

C Step 6

D Step 9

💡 Hint

Look for 'Error: Service not found' in the Result/Output column.

If the service list changes, which variable in variable_tracker updates?

A command

B service_list

C call_response

D service_type

💡 Hint

See the 'service_list' row in variable_tracker for changes after 'rosservice list' commands.

Concept Snapshot

rosservice command-line tool lets you interact with ROS services.
Common commands: list (shows all services), type (shows service type), call (calls a service with parameters).
Use YAML format for parameters in call.
Errors occur if service name is wrong.
Outputs show service info or call results.

Full Transcript

The rosservice command-line tool helps users interact with ROS services by typing commands in the terminal. When a user runs rosservice with a command like list, type, or call, the tool parses the input, checks what the user wants, and performs the action. For example, 'rosservice list' shows all active services. 'rosservice type /add_two_ints' shows the type of that service. 'rosservice call /add_two_ints "a: 2\nb: 3"' sends parameters to the service and shows the response. If the service name is wrong, rosservice shows an error. This step-by-step flow helps users understand how rosservice commands work and what outputs to expect.

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