Control when subsystem or model executes Show
A conditionally executed subsystem, also known as a conditional subsystem, is a nonvirtual subsystem that allows you to control its execution with an external signal. The external signal, called the action signal or control signal, is attached to the action input or control input port. Conditional subsystems are useful when you create complex models that contain components whose execution depends on other components. Simulink® supports these types of conditional subsystems:
Simulink also supports the Resettable Subsystem, which executes at each time step but resets all blocks within the subsystem to their initial condition when the control signal rises or falls to zero or crosses zero. See Using Resettable Subsystems. You can configure a referenced model for conditional execution like a subsystem. See Conditionally Execute Referenced Models. Blocksexpand all Action SubsystemsEnabled and Triggered SubsystemsFunction-Call SubsystemsResettable SubsystemsFunctionsTopicsTypes of Conditionally Executed Subsystems
Subsystem Output Initialization
Featured ExamplesSkip to main content This browser is no longer supported. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. Everything you wanted to know about the if statement
In this articleLike many other languages, PowerShell has statements for conditionally executing code in your scripts. One of those statements is the If statement. Today we will take a deep dive into one of the most fundamental commands in PowerShell. Conditional executionYour scripts often
need to make decisions and perform different logic based on those decisions. This is what I mean by conditional execution. You have one statement or value to evaluate, then execute a different section of code based on that evaluation. This is exactly what the The if statementHere is a basic example of the
The first thing the In the previous example, the In some languages, you can place a single line of code after the Comparison operatorsThe most common use of the -eq for equalityThe
In this example, I'm taking a known value of One possible use case is to check the status of a value before you take an action on it. You could get a service and check that the status was running before you called It's common in other languages like C# to use This operator (and others) has a few variations.
-ne not equalMany operators have a related operator that is checking for the opposite
result.
Use this to make sure that the action only executes if the value isn't Variations:
These are inverse variations of -gt -ge -lt -le for greater than or less thanThese operators are used when checking to see if a value is larger or smaller than another value. The
Variations:
I don't know why you would use case-sensitive and insensitive options for these operators. -like wildcard matchesPowerShell has its own wildcard-based pattern matching syntax and you can use it with the
It's important to point out that the pattern matches the whole string. If you need to match something in the middle of the
string, you need to place the
Variations:
-match regular expressionThe
A regex pattern matches anywhere in the string by default. So you can specify a substring that you want matched like this:
Regex is a complex language of its own and worth looking into. I talk more about Variations:
-is of typeYou can check a value's type with the
You may use this if you're working with classes or accepting various objects over the pipeline. You could have either a service or a service name as your input. Then check to see if you have a service and fetch the service if you only have the name.
Variations:
Collection operatorsWhen you use the previous operators with a single value, the result is
This still works correctly in a
There's one small
trap hiding in the details here that I need to point out. When using the
This may look like a clever trick, but we have operators -containsThe
This is the preferred way to see if a collection contains your value. Using Variations:
-inThe
Variations:
Logical operatorsLogical operators are used to invert or combine other expressions. -notThe
Most of the operators we talked about do have a variation where you do not need to use the ! operatorYou can use
You may see -andYou can combine expressions with the
In that example,
Evaluation happens from left to right. If the first item evaluates to
-orThe
Just like with the Also make note of how the syntax works for these operators. You need two separate expressions. I
have seen users try to do something like this -xor exclusive orThis one is a little unusual. It's rare that anyone would ever use this logical operator and I can't think up a good example as to why I would ever use it. Bitwise operatorsBitwise operators perform calculations on the bits within the values and produce a new value as the result. Teaching bitwise operators is beyond the scope of this article, but here is the list the them.
PowerShell expressionsWe can use normal PowerShell inside the condition statement.
It evaluates to
These expressions can be combined with each other with the
Checking for $nullHaving a no result or a
There are quite a few nuances when dealing with Variable assignment within the conditionI almost forgot to add this one until Prasoon Karunan V reminded me of it.
Normally when you assign a value to a variable, the value isn't passed onto the pipeline or console. When you do a variable assignment in a sub expression, it does get passed on to the pipeline.
See how the
If Make sure you don't confuse this with Variable assignment from the scriptblockYou can also use the
Each script block is writing the results of the commands, or the value, as output. We can assign the result of the Alternate execution pathThe elseThe
In this example, we check the
Nested ifThe
In this example, we test the happy path first and then take action on it. If that fails, we do another check and to provide more detailed information to the user. elseifWe aren't limited to just a single conditional check. We can chain
The execution happens from the top to the bottom. The top switchAt this point, I need to mention the
There three possible values that can match the Array inlineI have a function called Invoke-SnowSql that launches an executable with several command-line arguments. Here is a clip from that function where I build the array of arguments.
The Simplify complex operationsIt's inevitable that you run into a situation that has way too many comparisons to check and your
They can be hard to read and that make you more prone to make mistakes. There are a few things we can do about that. Line continuationThere some operators in PowerShell that let you wrap you command to the next line. The logical operators
There's still a lot going on there, but placing each piece on its own line makes a big difference. I generally use this when I get more than two comparisons or if I have to scroll to the right to read any of the logic. Pre-calculating resultsWe can take that statement out of the
This just feels much cleaner than the previous example. You also are given an opportunity to use a variable name that explains what it's that you're really checking. This is also and example of self-documenting code that saves unnecessary comments. Multiple if statementsWe can break this up into multiple statements and check them one at a time. In this case, we use a flag or a tracking variable to combine the results.
I did have to invert the logic to make the flag logic work correctly. Each evaluation is an individual The obvious downside is that it's so much more code to write. The code is more complex to look at as it takes a single line of logic and explodes it into 25 or more lines. Using functionsWe can also move all that validation logic into a function. Look at how clean this looks at a glance.
You still have to create the function to do the validation, but it makes this code much easier to work with. It makes this code easier to test. In your tests, you can mock the call to The body of that function could still be that one-liner we started with or the exploded logic that we used in the last section. This works well for both scenarios and allows you to easily change that implementation later. Error handlingOne important use of the
I like to say that if you expect an exception to happen, then it's not really an exception. So check your values and validate your conditions where you can. If you want to dive a little more into actual exception handling, I have an article on everything you ever wanted to know about exceptions. Final wordsThe FeedbackSubmit and view feedback for When an if statement is placed within the conditionally executed code of another if statement this is known as a N?8. When an if statement is placed within the conditionally-executed code of another if statement, this is known as nesting.
What is the difference between an if statement an IF ELSE statement and an IF ELSE IF statement quizlet?. In an if/else if statement, the conditions are tested until one is found to be true. The conditionally executed statement(s) are executed and the program exits the if/else if statement. In a series of if statements, all of the if statements execute and test their conditions because they are not connected.
Why does Visual Studio automatically indent the conditionally executed statements in a decision structure?Why does Visual Studio automatically indent the conditionally executed statements in a decision structure? Because, when the conditionally executed statements are intended, the statements are visually clear and this makes code easier to read.
Which if statement allows you to properly check the char variable code to determine whether it is equal to AC and then output this is a check?Which statement allows you to properly check the char variable code to determine whether it is equal to a "C" and then output. "This is a check" and then advance to a new line? cout << "This is a check\n"; What is the value of the following expression?
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