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Logger

5:44 with Jason Seifer

As we've been going along coding programs so far, when we need to know the value of a variable or debug some piece of data, we've generally been using print or puts statements of some sort. This works just fine for smaller programs. However, as you start to write larger programs, it can be cumbersome and sometimes ineffective to stop the program and print things to the screen. In cases like this, we can use something called log to write data to a stream. The stream can be a file, standard output, the network, and more. We can write things like the current state of our classes and objects, errors, and more. The Ruby standard library comes with logging functionality in the form of the Logger class from the Standard Library

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As we've been going along coding programs so 0:00

far, when we need to know the value of a variable, or debug some piece of data, 0:03

we've generally been using print or put statements some of the time. 0:08

This works just fine for smaller programs. 0:14

However as you start to write larger programs, it can be cumbersome and 0:16

sometimes ineffective to stop the program and print things to the screen. 0:21

In cases like this, we can use something called a log to write data to a stream. 0:27

The stream can be a file, standard output, the network, and more. 0:33

We can write things like the current state of our classes and 0:39

objects, errors, and several other things. 0:42

The Ruby standard library comes with logging functionality 0:46

in the form of the logger class. 0:50

Let's go ahead and take a look at how to use that now using workspaces. 0:53

So the next thing we're going to take a look at is the logger. 0:59

Now, logs are really, really useful to have when you are programming. 1:02

You can print out different messages to the log 1:06

and it can really, really help when you're debugging something. 1:11

So, let's go ahead and take a look at how to do this. 1:14

Now, if we read about the logger here, 1:17

it says it provides a simple but sophisticated logging utility 1:20

that we can use to output messages, 1:23

and they have associated levels like info or error that indicate their importance. 1:26

So here are the different levels that are built in: unknown, fatal, error 1:32

warn, info and debug. 1:37

Now, generally when you deploy an application to production, 1:40

you won't have debugging on, or have warning, errors, fatals and 1:43

so forth, all the way up the warn chain. 1:47

Now, let's go ahead and create a logger. 1:51

Now, we're going to do this inside of irb, 1:54

first we have to require the logging class. 1:57

Now we could log to files, but for right now, 2:02

we're going to log to STDOUT to see how that works. 2:05

Okay, so we get back this logger instance. 2:09

And now what we can do is send messages to it in the form of a string. 2:12

So we could say logger.info "This is an info message". 2:17

And now, we get this little I right here, it stands for the level info, 2:24

we get the timestamp of the message, and then once again we get the full level 2:28

and the message. And this log statement's gonna return true. 2:34

Now, we have methods for each different level, so, 2:40

logger.debug "This is a debugging message". 2:43

And now we get that D, DEBUG, debugging message. 2:47

Same thing with warnings 2:53

and fatal messages. 2:58

Now we're not limited to just standard output when we create one of these. 3:03

Let's go ahead and create another logger. 3:08

And that will log to just log.txt. 3:10

And now we can send messages to this as well, logger.info 3:16

"This is a test", 3:20

and we get back the message true. 3:23

Now if I were to refresh this file list, we have this log.txt right here, 3:25

and we open it up, it says when the log file was created, what it was created by, 3:32

and here are our log messages. 3:37

So I could do something like name = "Jason" 3:40

logger.info "The name is #{name}". 3:43

Now if I reopen this log file here, it says The name is Jason. 3:50

Now we can use a logger in our own programs, 3:56

and here's an example of logger.rb. 3:59

Now this is just a very, very simple BankAccount class. 4:04

It has an attr_accessor for the name, and then readers for the logger 4:08

and the different transactions. 4:13

So we're creating a new log that logs to the account.txt file. 4:15

Now, whenever we deposit or withdraw money, we have a logger statement 4:19

that puts it into the log and then applies the transaction. 4:25

So now we can instantiate that, and then when we deposit or withdraw money, 4:30

we should get a log statement. 4:36

Now, this program isn't gonna have any output, but we're just gonna run it 4:38

with logger.rb. 4:43

And now we should be able to refresh this file list, 4:48

and open up account.txt, 4:51

and we have our two info messages that say I deposited 100 dollars, 4:54

and withdrew 50. 5:00

That logging is extremely useful and hopefully this example 5:02

demonstrated, just a little bit, about how you'd wanna use a logger in your own program. 5:06

Great job. 5:11

In this course we've learned a little bit about Ruby's core and standard libraries. 5:12

We've seen a few examples of what's inside them, and where to go to find out more. 5:18

But don't stop now. 5:23

We've only covered a few parts, and 5:25

there's a lot of functionality in the standard library. 5:26

Try reading more about the standard library by checking out 5:30

the different classes available using the links to the documentation provided. 5:33

And don't be afraid to try them out on your own using WorkSpaces. 5:38

Good job, and happy coding. 5:42

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Ruby Core and Standard Library

Logger

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