# PowerShell Quick Reference

*Cmdlets, pipeline, objects, scripting, modules*

> Source: PowerShell Documentation (learn.microsoft.com/powershell) · MIT

## Basics

### Commands & Help

```
Get-Help Get-Process         # show help for cmdlet
Get-Help Get-Process -Online # open online docs
Get-Command *service*        # find commands by name
Get-Alias ls                 # show alias target
```

### Common Aliases

| Command | Description |
|---------|-------------|
| `ls → Get-ChildItem` | List files and directories |
| `cd → Set-Location` | Change directory |
| `cp → Copy-Item` | Copy file or directory |
| `mv → Move-Item` | Move or rename |
| `rm → Remove-Item` | Delete file or directory |
| `cat → Get-Content` | Read file contents |
| `echo → Write-Output` | Print to pipeline |
| `cls → Clear-Host` | Clear console |

## Variables

### Variable Basics

```
$name = "Alice"          # string
$count = 42              # integer
$pi = 3.14              # double
$list = @(1, 2, 3)      # array
$hash = @{a=1; b=2}     # hashtable
```

### Automatic Variables

| Command | Description |
|---------|-------------|
| `$_` | Current pipeline object |
| `$PSVersionTable` | PowerShell version info |
| `$HOME` | User's home directory |
| `$PWD` | Current directory |
| `$null` | Null value |
| `$true / $false` | Boolean constants |
| `$Error` | Array of recent errors |
| `$LASTEXITCODE` | Exit code of last native command |

### Environment Variables

```
$env:PATH                     # read env var
$env:MY_VAR = "value"         # set env var
Get-ChildItem Env:            # list all env vars
```

## Operators

### Comparison Operators

| Command | Description |
|---------|-------------|
| `-eq  -ne` | Equal / not equal |
| `-gt  -lt` | Greater / less than |
| `-ge  -le` | Greater/less or equal |
| `-like  -notlike` | Wildcard match (`*`, `?`) |
| `-match  -notmatch` | Regex match |
| `-contains` | Collection contains value |
| `-in  -notin` | Value in collection |

### Logical & Other Operators

| Command | Description |
|---------|-------------|
| `-and  -or  -not` | Logical operators |
| `!` | Logical NOT (alias) |
| `-replace` | Regex replace: `'hi' -replace 'h','b'` |
| `-split  -join` | Split / join strings |
| `..` | Range: `1..5` → 1,2,3,4,5 |
| `?:` | Ternary (v7+): `$x ? 'yes' : 'no'` |

## Control Flow

### if / elseif / else

```
if ($age -ge 18) {
    "Adult"
} elseif ($age -ge 13) {
    "Teen"
} else {
    "Child"
}
```

### switch

```
switch ($color) {
    "red"   { "Stop" }
    "green" { "Go" }
    default { "Unknown" }
}
```

### Loops

```
foreach ($item in $list) { $item }
for ($i=0; $i -lt 5; $i++) { $i }
while ($x -lt 10) { $x++ }
1..5 | ForEach-Object { $_ * 2 }
```

## Functions

### Defining Functions

```
function Get-Greeting {
    param([string]$Name = "World")
    "Hello, $Name!"
}
Get-Greeting -Name "Alice"
```

### Advanced Parameters

```
function Copy-SafeFile {
    [CmdletBinding()]
    param(
        [Parameter(Mandatory)][string]$Path,
        [Parameter(Mandatory)][string]$Dest
    )
    Copy-Item $Path $Dest -WhatIf:$WhatIfPreference
}
```

## Objects & Pipeline

### Pipeline Basics

```
Get-Process | Sort-Object CPU -Desc | Select-Object -First 5
Get-Service | Where-Object Status -eq "Running"
Get-ChildItem | Measure-Object -Property Length -Sum
```

### Key Pipeline Cmdlets

| Command | Description |
|---------|-------------|
| `Where-Object` | Filter objects: `\| Where {$_.CPU -gt 10}` |
| `Select-Object` | Pick properties: `\| Select Name, CPU` |
| `Sort-Object` | Sort: `\| Sort CPU -Desc` |
| `ForEach-Object` | Transform each: `\| ForEach {$_.Name}` |
| `Measure-Object` | Count, sum, average, min, max |
| `Group-Object` | Group by property value |
| `Format-Table` | Display as table: `\| ft -Auto` |
| `Export-Csv` | Export to CSV: `\| Export-Csv out.csv` |

## Files

### File Operations

```
Get-Content log.txt                    # read file
Set-Content out.txt "hello"            # write (overwrite)
Add-Content out.txt "more"             # append
Get-Content log.txt | Select-String "error"  # grep
```

### Path & File Cmdlets

| Command | Description |
|---------|-------------|
| `Test-Path $path` | Check if file/dir exists |
| `New-Item -Type File` | Create file |
| `New-Item -Type Directory` | Create directory |
| `Resolve-Path` | Get absolute path |
| `Join-Path` | Combine path segments |
| `Split-Path` | Get parent or leaf |
| `Get-ItemProperty` | File attributes and metadata |
| `Remove-Item -Recurse` | Delete directory recursively |

## Strings

### String Basics

```
"Hello, $name"                # interpolation (double quotes)
'Hello, $name'                # literal (single quotes)
"Length: $($list.Count)"       # expression in string
@"
Multi-line
here-string with $name
"@
```

### String Methods

| Command | Description |
|---------|-------------|
| `.ToUpper() / .ToLower()` | Change case |
| `.Trim()` | Remove leading/trailing whitespace |
| `.Split(',')` | Split into array |
| `.Replace('a','b')` | Replace substring |
| `.StartsWith() / .EndsWith()` | Check prefix / suffix |
| `.Substring(0,5)` | Extract substring |
| `.Contains('text')` | Check if contains |
| `-f operator` | `'{0} is {1}' -f 'sky','blue'` |

## Modules

### Module Management

```
Get-Module -ListAvailable           # installed modules
Find-Module -Name Az*               # search gallery
Install-Module -Name Pester         # install from gallery
Import-Module ActiveDirectory       # load module
```

### Module Commands

| Command | Description |
|---------|-------------|
| `Get-Module` | List loaded modules |
| `Import-Module` | Load module into session |
| `Remove-Module` | Unload module from session |
| `Update-Module` | Update installed module |
| `Get-Command -Module X` | List commands in module |
| `$env:PSModulePath` | Module search paths |

## Common Patterns

### Error Handling

```
try {
    Get-Item "C:\missing" -ErrorAction Stop
} catch {
    "Error: $_"
} finally {
    "Cleanup here"
}
```

### Execution Policy & Remoting

| Command | Description |
|---------|-------------|
| `Get-ExecutionPolicy` | Show current script policy |
| `Set-ExecutionPolicy RemoteSigned` | Allow local scripts |
| `Enter-PSSession -Computer SRV1` | Interactive remote session |
| `Invoke-Command -Computer SRV1 -Script {}` | Run script block remotely |
| `Start-Job { long-task }` | Run background job |
| `Receive-Job -Id 1` | Get background job output |