[S] Suspend in Visual C#.NET

Creator Code 39 Full ASCII in Visual C#.NET [S] Suspend

The interpreter displays the line to be executed, then asks the user to select one of Yes, Yes to All, No, or No to All. The default is Yes . If you answer Yes , then that line will be executed and you will be prompted as to whether you want to execute the next line. If you answer Yes to All , then step mode will be turned off and execution will continue normally. If you answer either No or No to All , the current execution will be stopped and you will be returned to the command prompt. There is no difference in the behavior between No and No to All . The following shows the message you will see if you enter No .

Continue with this operation 2+ $x = $args[0] [Y] Yes [A] Yes to All [N] No [ ] Help(default is "Y"): y DEBUG: 2+ $x = $args[0] DEBUG: ! SET $x = '2'. Continue with this operation 3+ "x is $x" } [Y] Yes [A] Yes to All [N] No

[ ] Help(default is "Y"): l WriteDebug stopped because the DebugPreference was 'Stop'. At line:1 char:23 + foreach ($i in 1..3) {f <<<< oo $i} PS (16) >

As you can see, this is a pretty limited feature. Full debugging was cut from version one of PowerShell. We were only able to provide the most basic features. This will be corrected in future releases. We didn t even get a chance to make what s there pretty. It is, however, still useful.

There is one more option in the stepping list that we haven t talked about yet, and that is Suspend . This option is interesting enough to merit its own section, and is discussed in section 9.4. In the meantime, let s finish our discussion of the SetPSDebug debugging features. 9.3.5 Catching undefined variables with strict mode The last debugging feature accessible through Set-PSDebug is strict mode .

This feature is conceptually similar to Option Explicit in Visual Basic or strict mode in PERL, and is named after the PERL feature, though it s not as rigorous as either the VB or PERL features. Still, it can make it easier to write a robust script.

Normally in PowerShell, if a variable is undefined, it s treated as though it has the value $null. We can try this in an expression.

In this expression, $nosuchvariable is not defined. This means that it is treated as though it were $null. And $null in a numeric expression is treated as zero, so the whole expression evaluates to zero. It is important to note that the variable is treated as though it were null. This doesn t mean that there is now a variable called $nosuchvariable. We can verify this with the dir command:

PS (2) > dir variable:\nosuchvariable Get-ChildItem : Cannot find path 'nosuchvariable' because it doe s not exist. At line:1 char:4 + dir <<<< variable:\nosuchvariable

and try the expression again:

PS (4) > 2 * $nosuchvariable The variable $nosuchvariable cannot be retrieved because it has not been set yet. At line:1 char:19 + 2 * $nosuchvariable <<<<

This time, you are sent an error telling you that the variable has not been defined. So let s define it.

Run the expression again:

We get the expected result. Delete the variable:

PS (8) > 2 * $nosuchvariable The variable $nosuchvariable cannot be retrieved because it has not been set yet. At line:1 char:19 + 2 * $nosuchvariable <<<<

One of the more interesting aspects of dynamic language environments is that a script can recursively call the interpreter. We ve already seen this with the InvokeExpression cmdlet in chapter 8. A variation of this is to call the interpreter in interactive mode. This means that you essentially suspend the current session and start a new session. In other words, you can suspend the currently executing PowerShell code and interact with PowerShell at what is called a nested prompt. Why is this interesting Because now you can type commands that can examine and modify the state of the suspended session. And instead of creating a language just for debugger operations, you use the same language you re debugging. There are a couple ways to enter a nested prompt session, as we ll see in the next couple sections.

Suspending a script while in step-mode Creating a nested interactive session is what the Suspend operation does. Let s try it out. First turn on stepping: