# Flow Control (All in one)
Flow control statements allow you to control the execution of your scripts based on conditions, loops, and switches. PowerShell provides several flow control constructs, including **If-ElseIf-Else**, **While**, **Do-While**, **ForEach**, **For**, and **Switch**. Each of these constructs serves a specific purpose and can be used to make your scripts more dynamic and efficient.
***
#### **1. If-ElseIf-Else**
**Definition**
The **If-ElseIf-Else** statement is used to execute different blocks of code based on one or more conditions. It evaluates a condition, and if the condition is `$true`, the corresponding block of code is executed. If the condition is `$false`, it moves to the next condition (`ElseIf`) or executes the `Else` block if no conditions are met.
**Example**
```
$string = "SANS has GIAC training for the GCWN cert."
If ($string -like "SANS*") {
"It's true that it starts with SANS."
} ElseIf ($string -match "[FGH]IAC") {
"It matches the regular expression pattern."
} ElseIf ($string -eq "GCWN") {
"It matches the string exactly."
} Else {
"None of the above tests resolved to $true."
}
```
***
#### **2. While Loop**
**Definition**
The **While** loop repeatedly executes a block of code as long as a specified condition is `$true`. If the condition is `$false` initially, the loop will not execute at all.
**Example**
```
$rabbits = 2
While ($rabbits -lt 10000) {
"We now have $rabbits!"
$rabbits = $rabbits * 2
}
```
**Example with Scheduled Task**
```
Start-ScheduledTask -TaskPath "\SEC505\" -TaskName "SetUID"
$Task = Get-ScheduledTask -TaskName "SetUID"
While ($Task.State -eq "Running") {
"Task Still Running: " + (Get-Date).DateTime
Start-Sleep -Seconds 10
$Task = Get-ScheduledTask -TaskName "SetUID"
}
"Task Completed: " + (Get-Date).DateTime
```
***
#### **3. Do-While Loop**
**Definition**
The **Do-While** loop is similar to the **While** loop, but it guarantees that the block of code will execute at least once, even if the condition is `$false` initially.
**Example**
```
$rabbits = 2
Do {
"We now have $rabbits!"
$rabbits *= 2
} While ($rabbits -lt 10000)
```
**Example with Web Server Monitoring**
```
Do {
$Result = Test-NetConnection -ComputerName 10.1.1.1 -Port 80
Start-Sleep -Seconds 60
} While ($Result.TcpTestSucceeded)
"Web Server Test Failure: " + (Get-Date).DateTime
```
***
#### **4. ForEach Loop**
**Definition**
The **ForEach** loop is used to iterate over a collection or array. It processes each item in the collection one by one.
**Example**
```
$Services = Get-Service
ForEach ($Svc in $Services) {
$Svc.Name + ": " + $Svc.Status
}
```
**Example with Pipeline**
```
Get-Service | ForEach-Object { $_.Name + ": " + $_.Status }
```
***
#### **5. For Loop**
**Definition**
The **For** loop is used to execute a block of code a specific number of times. It consists of three parts: initialization, condition, and increment.
**Example**
```
For ($i = 0; $i -le 20; $i++) {
"Now at $i"
}
```
**Example with Complex Logic**
```
For ($i = 0, $j = 0; $i -lt 10; $i++, $j += 2) {
"i = $i, j = $j"
}
```
***
#### **6. Switch Statement**
**Definition**
The **Switch** statement is used to compare a value against multiple conditions. It can handle exact matches, wildcards, and regular expressions.
**Example**
```
$x = 58
Switch ($x) {
{$_ -lt 20} { "Really Small" }
{$_ -gt 50} { "Pretty Big" }
58 { "It's 58" }
Default { "What was that?" }
}
```
**Example with Wildcards**
```
Switch -Wildcard ("c:\data5\archive.zip") {
'?:\data?\*' { "In some data folder." }
'*.zip' { "File is a ZIP." }
}
```
**Example with Regular Expressions**
```
Switch -Regex ("c:\data5\archive.zip") {
'\\data[0-9]+\\' { "In some data folder." }
'\.ZIP$|\.BKF$|\.TAR$' { "File is a ZIP or BKF or TAR." }
}
```
**Example with Arrays**
```
$stopped = $running = $paused = 0
Switch (Get-Service) {
{$_.Status -like "Running"} { $running++ }
{$_.Status -like "Stopped"} { $stopped++ }
{$_.Status -like "Paused"} { $paused++ }
}
"Services Running = $running"
"Services Stopped = $stopped"
"Services Paused = $paused"
```
**Example with Text Files**
```
$HashTable = @{}
Switch -RegEx -File .\pfirewall.log {
"DROP\sTCP.+RECEIVE" {
$SrcIP = ($_ -Split " ")[4]
If ($HashTable.ContainsKey($SrcIP)) {
$HashTable.Item($SrcIP) = $HashTable.Item($SrcIP) + 1
} Else {
$HashTable.Add($SrcIP, 1)
}
}
}
$HashTable.GetEnumerator() | Sort-Object Value -Descending
```
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