TopolearnThese five cmdlets answer most 'which ones, how many, the biggest' questions about any data.
Once data is objects, a handful of cmdlets do most of the work:
- Where-Object filters:
Where-Object { $_.Length -gt 1MB }. Inside the script block,$_(or$PSItem) is the current object. For a single comparison the simplified formWhere-Object Length -gt 1MBalso works. - Sort-Object orders by one or more properties:
Sort-Object Length -Descending. - Select-Object picks properties (
Select-Object Name, Length), takes-First/-Lastitems, removes duplicates with-Unique, and-ExpandProperty Namereturns the bare values instead of objects with one property. - Group-Object groups by a property and counts.
- Measure-Object computes count, sum, average, minimum and maximum.
Calculated properties add or rename columns: @{ Name = 'KB'; Expression = { $_.Length / 1KB } }. Size suffixes KB, MB, GB are built-in numeric literals.
Filter left: when a cmdlet has its own filter parameter, such as Get-ChildItem -Filter *.log or Get-Process -Name pwsh, use it. The provider or API does the filtering before objects are created, which can be dramatically faster than Where-Object on large sets, especially against remote systems.
Example
$files = Get-ChildItem $PSHOME -File
$files | Where-Object { $_.Length -gt 1MB } | Measure-Object |
Select-Object -ExpandProperty Count # how many files > 1 MB
$files | Where-Object Extension -eq '.json' |
Select-Object -First 2 -ExpandProperty Name # simplified syntax
$files | Sort-Object Length -Descending | Select-Object -First 3 Name,
@{ Name = 'KB'; Expression = { [math]::Round($_.Length / 1KB) } }
$files | Group-Object Extension | Sort-Object Count -Descending |
Select-Object -First 3 Count, Name # most common extensions
$files | Measure-Object Length -Sum -Maximum | Select-Object Count, Sum, Maximum
Get-ChildItem $PSHOME -Filter *.json # filter left: provider does itRemember
- Where-Object filters, Sort-Object orders, Select-Object picks
- $_ is the current object inside script blocks
- Use a cmdlet's own -Filter or -Name parameter before Where-Object
Watch out for
- Expecting
Select-Object Nameto return strings; it returns objects with a Name property. Use -ExpandProperty.