1. PowerShell
Flow of Control
Copyright © 2016 – Curt Hill

2. Introduction
We have seen some of the basics of scripting now onto flow of control
Everyone in this class knows C++ and one or more additional programming languages
Covering flow of control should be comparatively easy
The syntax may be different than what you have seen previously but the concepts should be easy to understand
Copyright © 2016 – Curt Hill

3. Blocks
PowerShell uses the braces { } in a similar way as the C family of languages
They create a block of statements that is considered as a unit for inclusion in a decision or looping statement
In the console entering a { keeps the item from being executed until the terminal brace is entered
The scope rules are different from C++ and more similar to C
Will be discussed later
Copyright © 2016 – Curt Hill

4. Conditions
Flow of control statements typically need some type of expression that generates a true/false value to drive them
This is a problem for the traditional comparisons < and > are special characters for PowerShell
Therefore PowerShell uses a FORTRANish set of operators
Copyright © 2016 – Curt Hill

5. Comparison Operators
Use a dash followed by two letters to indicate the operator
== is –eq
< is –lt
<= is –le
!= is –ne
> is –gt
>= is –ge
Copyright © 2016 – Curt Hill

6. Logical Operators We also have Boolean operators: Not is –not
And is –and
Or is –or
Exclusive or is –xor
Copyright © 2016 – Curt Hill

7. Other Operators
There are others that are neither comparison nor Boolean operators
Yet still handy
-like and –notlike
Uses wildcards
-match and –notmatch
Uses regular expressions
-in and –notin
-contains and –notcontains
-is and –isnot
Copyright © 2016 – Curt Hill

8. Case Sensitivity These operators are not case sensitive
As are most MicroSoft comparisons
If case sensitivity is desired prefix the operator with a c
Thus:
$item –eq “stuff” is case insensitive
$item –ceq “Stuff” is case sensitive
Copyright © 2016 – Curt Hill

9. Example
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10. Decisions The language contains several flow statements If Switch For
While Do
foreach
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11. If
Other than the condition the simple forms look like C if($t –eq $other) { … } else { … }
Do I need to say more?
Copyright © 2016 – Curt Hill

12. Yes, I do PowerShell requires the braces after the then or else
Makes parsing easier
PowerShell also has an elseif
Often used to reduce braces for nested if then elses
Copyright © 2016 – Curt Hill

13. Examples
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14. Switch Allows certain types of nested if then elses to be collapsed
Different than that of C in that it is more clearly a modified if
No case keyword instead use a conditional expression that references $_ which is the path selector
Consider the following example
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15. Switch example
Clear enough?
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16. For loops
Very similar to that of C with the exception of variable names and conditionals
See the next slide
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17. For example
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18. Whiles Similarly the while and do while look like those of C
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19. While Example
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20. Do While Example
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21. More There is also a Pascalish Do Until
Same as do while except condition is reversed
Do while quits when condition is false
Do until quits when condition is true
Copyright © 2016 – Curt Hill

22. Foreach The foreach is an iterator through a collection
The most interesting collections are returned by other objects
Such as files in a directory
You may create a collection with a comma separated list or a subrange
Then the in operator may be used
Copyright © 2016 – Curt Hill

23. Collections
A subrange is two numeric values separated by a two dot ellipsis, such as: 4..9
If these are non-integer they will be truncated to an integer
A comma separated list may be of any type
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24. Example
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25. Finally
There are a few more things that we have to wait for a subsequent presentation
Copyright © 2016 – Curt Hill