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In this video, we'll investigate some advanced scripting options.

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So here you can see the example script.

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Let me type it for you so that we can talk about its contents.

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Calling it script 3.

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And as always, starting with the shebang.

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And then I'm defining a variable counter is $1.

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As we have seen in the previous script, $1 is the first argument that you are using.

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And here I'm going to put the value of $1 in a variable with the name counter.

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Why do I do that?

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Well, because I want to be able to change the value of the variable.

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And you cannot change values of variables that have been provided as an argument.

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We call these positional parameters, by the way.

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So $1 is the positional parameter.

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And the value of $1 was determined while you started the script.

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So you can't multiply the value of $1 by 60, which is what I'm doing right here.

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By putting your calculation between $ and double parentheses, you perform the calculation.

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And here the result will be that counter has a certain value.

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And counter times 60 is multiplying it by 60.

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Then I'm going to define $-1.

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That's a function.

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Now, what is the purpose of a function?

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The function is like an internal command, and it makes writing your script a little

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bit easier.

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I know beforehand that I am going to need a lot of counter $-1, which is followed by

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the command sleep 1.

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And in order to make it easy to call these commands, I'm putting them in a function.

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So the function name is $-1.

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And then I'm just calling the function name further on within my script.

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Next, I'm using while square brackets $counter minus gt 0.

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That's an integer test where I'm going to stay in the loop as long as the value of the

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variable counter is greater than the integer value of 0.

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Next, we need a do.

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And then I'm going to use echo.

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You still have $counter seconds left.

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And then I'm going to call the function minus 1, because I want to subtract 1 from the current

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value of the variable.

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And I want to sleep for 1 second so that this script is properly going to count down.

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Oops, I just noticed that I have a typo on line 1.

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Good.

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Next, I am going to use $counter equals 0, double ampersand, echo, time is up, n minus

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1.

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Couple of things in this line.

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First, we have the test counter is 0.

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Now, if you have a sharp eye or if you have worked with other scripting languages, you

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might have expected $counter minus eq 0, because minus eq is for integers and equals is for

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string.

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Now, the thing is that in bash scripts, you don't work with variable types.

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You can just work with the variable according to its context.

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So there is no fundamental difference between $counter equals 0 and $counter minus eq 0,

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because it needs to have the value of 0.

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And the integer 0 can also be considered as a string 0.

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It's not as in Python, where you really need a specific type, and if you address the wrong

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type, it fails.

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Then we have the double ampersand.

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The double ampersand is a logical and.

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And the logical and means that echo, time is up, will only be executed if the first

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command was true.

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So you can read it as if square bracket counter is 0, then echo, time is up.

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And then it continues with another double ampersand, which is continuing the minus 1.

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These double ampersands or logical ands allow you to write compact if-then-else statements.

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Then I need one more, where I'm going to work on a counter is minus 1, double ampersand,

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echo, you are now one second late, and double ampersand minus 1.

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And then I'm entering a generic loop, while true.

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While true is as long as the command true can be executed successfully.

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Now the essence of the command true is that it always generates an exit code 0, so it's

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always executed successfully.

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So always, I'm going to do what?

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Well, echo, you are now, and then dollar curly brace, counter, hash, minus, curly brace,

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seconds late.

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Now what is this, what I'm doing with the counter variable this time?

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Well, I'm putting it between curly braces to apply a pattern-matching operator.

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And the pattern-matching hash minus is looking for the pattern minus at the beginning of the

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string and will remove it.

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The purpose of a pattern-matching operator is to remove a pattern.

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Now the thing is that we are minus 1 second late.

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I don't want to say you are now minus 1 seconds late, because if you are minus 1 seconds late,

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you are early.

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So the minus needs to be removed, and the pattern-matching operator is how this is done.

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Then I'm calling the function again.

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I'm closing the script, and we should be OK, and we should be able to run it.

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So chmod plus x on script 3, and then let's run it and see what it is doing.

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Oh, I don't have an argument, so it starts with a 0, and it immediately prints time is

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up.

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So I am providing the argument 1, and now you can see that it is nicely counting down.

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And this is my favorite countdown timer script.

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I use it in courses a lot to tell people how much time left in breaks.