Equivalent of Unix/Linux tail command for Powershell - that supports pipes?

Question

I'm aware that Get-Content has a -Tail parameter, but as far as I can tell, there's simply no way to get it to accept piped input.

So how do I get something like this to work? I just want to be able to select first X or last X lines from any preceding command, without the hassle of creating temp files simply so I can grab the first/last lines from it.

# This won't work as Get-Content demands a -Path to a file
Get-Item .\* | Get-Content -Tail 10

Some added finagling will likely be required depending on whether the first command is providing objects or strings as output; if you can include such intermediary steps in your reply, that'd be awesome. I expect something like Out-String -stream might be the done thing?

I've scoured the internet and came up empty-handed. Thanks in advance for any help.

Answer 1

PowerShell's pipeline is based on objects rather than lines of text, and Mathias R. Jessen's helpful answer has the object-oriented angle covered:

• Select-Object -First / -Last selects only the first / last N objects - whatever their type - and then renders them to the display using PowerShell's rich for-display output-formatting system.

• Given that the formatting of a single object can span multiple lines (consider the display output when you submit $PSVersionTable), there's no guarantee that the output will be limited to N lines.

If, by contrast, your intent is to limit the output to a given number of display lines - irrespective of how many objects the result corresponds to:

• Insert an Out-String call with the -Stream switch parameter before the Select-Object call. PowerShell v5+ even has a built-in wrapper function for this, oss.

• This performs the for-display formatting to a string, with -Stream then emitting the lines of the result one by one.

---

A simple example that illustrates the two approaches and how they differ:

# Create 10 sample objects that render with Format-List
# (each property on its own line)
$objects = 
  1..10 | ForEach-Object { [pscustomobject] @{ a=1*$_; b=2*$_; c=3*$_; d=4*$_; e=5*$_ } }

Write-Verbose -Verbose 'First 2 *objects*:'
# Select the first 2 *objects*, which are then rendered, 
# each with multiple lines.
$objects | Select-Object -First 2

Write-Verbose -Verbose 'First 2 *lines*:'
# Create the for-display representation as a string up front, 
# then select the first 2 *lines*
$objects | oss | Select-Object -First 2

This outputs the following:

VERBOSE: First 2 *objects*:

a : 1
b : 2
c : 3
d : 4
e : 5

a : 2
b : 4
c : 6
d : 8
e : 10

VERBOSE: First 2 *lines*:

a : 1

Note:

• PowerShell's output formatting often involves a leading and trailing empty line, which is why the output from the oss-based command starts with an empty line and only shows one property value (you could address that by eliminating blank lines as follows:
  $objects | oss | Where-Object { $_.Trim() } | Select-Object -First 2)

• An important use case for oss is quick-and-dirty text searches in object output via Select-String:

  • E.g., the following would show only the lines that contain the digit (string) 3:

    $objects | oss | Select-String '3'
    

    • Note that this technique is meant for convenient, interactive use only; for robustness, especially in scripts, using OO techniques for filtering, notably via Where-Object, is the right approach.

  • Sadly, Select-String doesn't have the oss stringification logic built in, even though it arguably should - see GitHub issue #10726.

Answer 2

You can use the Select-Object cmdlet to shape a piped input stream by using the -First/-Last parameters parameters, much like head/tail works in a Unix shell:

PS ~> 1..100 |Select-Object -First 5
1
2
3
4
5
PS ~> 1..100 |Select-Object -Last 5
96
97
98
99
100