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Hello, you beautiful people.

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And welcome to this video where you're going to take what you've learned about scripts in the last few

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videos and supercharge it by using Cron to make those scripts run on a schedule.

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It's going to be super awesome and over the next few videos you're going to make some batch scripts

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and schedule them to run automatically.

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And we're also going to top it off by showing you how you can schedule automatic backups of your files.

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So epic, right?

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So by the end of the next few videos, you're going to be able to automate your workflow by scheduling

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your scripts to run wherever you want.

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And this really does open the doors to untold awesomeness going forward.

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So let's go ahead and jump right into it.

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Okay.

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So Cron is a command line based program that is used to schedule tasks.

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Now Chrome gets its name from the Greek word Chronos, which means time, in case you were wondering.

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So Cron actually has quite a good name for a scheduling program.

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Right now each user has what is known as a cron tab, which basically is just a text file, and each

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cron tab lists which commands or scripts will be run automatically by that user.

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And it also lists when they will be scheduled to be run.

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Now to edit the cron tab for your user, you just open a command, open a terminal and type cron tab

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dash E and the E option is for edit.

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And when you open it you'll see that the cron tab begins to open.

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But if this is the first time that you're opening up a cron tab, it might ask you what editor you want

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to use.

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So we're just going to press one for nano and press enter and we will see that now we've opened up our

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cron tab in Nano.

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Now the first thing you'll notice is that there's a lot of text in here and this is a kind of introduction

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to how cron tabs work.

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But these are commented lines and what I mean by that is they are not interpreted by the CHRONOTYPE

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as actual valuable information.

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And you can tell that because they start each line with a hash and that allows, you know, people to

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write what they want in a file, like some notes, but it's not interpreted by the actual by the actual

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cron utility.

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But down the bottom, each cron tab is each cron tab is broken up into rows and one row is for each

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command or script that you want to schedule, and each row will have six columns.

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So the first five columns are scheduling information, and the final sixth column is the command or

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script to be run at that scheduled time.

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So you need to get in to the bottom and to enter your information.

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Okay, now this is really one of those things that's easier to be shown than explained.

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So let me show you how this works.

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So let's say that we want to run a command that just outputs the text.

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Hello world to a file called hello txt on our desktop and we want that command to run every minute of

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every day all year round because for some reason we just really like saying hello.

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Okay, so to make this happen, we need to enter a new row in our cron tab.

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And so here we are, we're on a new row and there are six columns in that row, each column being separated

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by some blank space.

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So let's take it step by step.

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Now, the first column of the row is for the it's for the minutes of the hour that you want the command

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to run on.

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So let's go to the first column.

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And we could put any number we want in here as long as it's a valid minute.

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So we could type 15, for example.

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Now, this would make the command run at 15 minutes past the hour.

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So things like 12, 15, two, 15, nine, 15, seven, 15 and so on.

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Okay, now the numbers for minutes can go from 0 to 59 because that's what numbers 4 minutes do on a

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normal clock.

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Right.

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So you can go from 0 to 59 now because we want the command to run every minute.

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We'll just put a star in there to say, run any minute now.

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No, this isn't exactly like a wild card.

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The star happens to mean any in this case, but crosstabs don't really support other wild cards, so

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don't put symbols such as question marks or the brackets in there because they won't work.

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The star is only what's accepted and it just means any value.

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We don't really care.

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So the first column is the minutes of the hour.

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The next column is the hour number.

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And we could put numbers like, for example, 11.

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So this would make it the command or whatever.

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We scheduled to only run the at 11 a.m. each day.

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We could put 14 so that it would only run at 2 p.m. each day.

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Now the numbers here are based on a 24 hour clock and can go from 0 to 23.

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And we but we don't mind particularly what our command runs at.

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So let's just put a star there as well.

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But if I put, for example, an 11 in the in the hour column and a 20 in the minute column, then our

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command would run at 11:20 a.m..

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So the first column is for the minutes and the second column is for the hours.

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And by the way, it doesn't really matter where we place these columns as long as there's some space

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between them.

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So we could like, you know, separate them out like that with more than one space.

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But as long as there's some blank space in between each of the columns, Cron isn't too fussy about

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how the about the how the stuff is laid out.

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So let me just try and make it a bit clearer which column we're filling in here.

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So there's the first column is minutes, seconds column.

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Hours and so on.

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I'm just going to kind of spread out our stuff a little bit here.

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So we got a bit of a nicer layout, but we don't really care about the minutes, so we'll put a star

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there.

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We don't really care about the hours, so we'll put a star there too.

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Now the third column is what we see here.

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Dom is the day of the month.

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So if we put a one here, then it would only run on the first day of the month.

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And so, for example, if we had a 20 in the minutes column and we had in the Hours column, we had

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an 11 and here we had a let's say a ten in the third column.

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Then this, then whatever command that we gave it would only run on the 10th day of the month at 1120,

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but it would run all of the months of the year, but only on the 10th day of the month at 11:20 a.m..

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But again, we don't really mind what day of the month.

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So we'll put a star there and we'll put a star in the other columns as well.

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There we go.

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So let's just lay this out a bit nicer.

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Okay, cool.

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Now, the fourth column is actually the month itself.

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Now, in here, we can put numbers, so we could put one being January, 12 being December and all the

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other months in between.

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But you could also do it using text.

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So for example, in capital letters, I could put Jan for January, February, for February I could

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do May or Dec for December.

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So three letter months can be used as well for for the month.

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If you write them in capital letters.

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But here we don't really care about in the month, so we're just going to put a start as well.

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And so just to see how this is all coming together, if we add a 20 in the first column and we had in

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the our column we had in 11 and in the day of the month we had a ten and in the month we had a June

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for June.

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Then this command would run on the 10th day of the month, on the 10th sorry, on the 10th of June at

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11:20 a.m..

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So that's that's how that works there.

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But we're going to replace them again with stars.

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So as I say, the the cron tab doesn't really care about the amount of space is just that each column

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is separated by at least one space.

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Okay, so, so there we go.

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The next column is the day of the week.

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Now the day of the week can have numbers from 0 to 6 with zero being Sunday and six being Saturday.

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But as well, you can do this doing text using three letters for each day of the week.

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So sun would be sun, mon would be Monday, THG would be Thursday, Saturday would be Saturday and so

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on.

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So let's say if we had a sun in there and the month was June and the day of the month was ten and then

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the hour was 11, and then the minute was 20.

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Then this would run at 11:20 a.m. on the 10th of June, as long as the 10th of June.

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On on that year was a Sunday.

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So you can see how you can become incredibly specific with how you schedule your commands to run.

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But you can also be very general and very relaxed as well.

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The cron tab, the cron utility is amazing for that kind of stuff.

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You can be very expressive with your scheduling.

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So there we go.

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We're going to set those back to stars because we don't care what day of the week it is.

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We want this command to run all day, every minute, all year round, so we don't really care.

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So those are the first five columns and these first five are scheduling information.

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Okay.

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Now the final bit is actually where you tell it the command or script that you want it to run.

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Okay.

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So the sixth and final column is the command to actually run.

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Now we said that we want a command that will output hello world to a file called hello text let's say

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on our desktop.

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So how would we write that.

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Well we might write Echo then.

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Hello World.

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And then we'd append that to somewhere on our desktop.

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A file called Hello Text.

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So if I just expand the window here, you'll be able to see it a bit better.

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There we go.

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So you can see here that we're just saying this is just the command basically echo hello world and put

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that on a file on a desktop called Hello Text.

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But we're using the two arrows here to allow whenever this command runs it will append data to the file

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so we can see extra data being added each time the command runs.

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Okay, so when we save the cron tab, so cron will make sure that this command is now run at every minute

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of every hour of every day of the month for every month, no matter the day of the week.

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So this command is going to run every minute, all year round.

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So if I press control in O to save that file and I exit, you can see here that we get a message saying

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that it's installing a new cron tab and we can see here that hello.

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TXT has actually just been has just been executed.

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Okay.

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So if we take a look, you can see that it actually just ran, right?

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Then we can see that it's actually executed.

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Hello world.

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And put it inside inside the inside the file.

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Now if I run the date command you can see that we've got about 40 seconds until this command runs again.

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So what I'm going to do is I'm going to cut the video here and come back closer to the time when that

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runs.

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Okay.

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So here we are.

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We can see that it's just gone.

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And literally as I press date, that's awesome.

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It's just past the minute.

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So if we look in there now, we should see that we now have two rows of data.

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So fingers crossed.

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Yes, we do.

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We now have two rows of data in there because the the the the cron tab has executed again right at the

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top of the hour and we'll just continue to wait until the next minute passes and it will continue to

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run that.

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It'll continue to run that that command over and over and over again and fill up this hello text file.

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Okay.

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Now, when when that actually runs, we'll see that more data has been added.

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We've got about 18.

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Also see if you can wait with me for like 18 seconds.

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We'll see this happen.

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Okay, so let's.

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Here we go.

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We're seeing another 11 seconds or so.

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Um, and now if I, if I check here, now we can see that there's 5 seconds to go.

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5 seconds to go.

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2 seconds to go.

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It should have done it now.

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So if we look inside, yep.

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It's run and it's added another row to the file and I didn't touch anything.

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I promise.

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So the Akron tab is working.

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Hooray!

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Okay, we've just made it run a command over and over and again.