PowerShell equivalent for "head -n-3"?

Question

I've been able to track down basic head/tail functionality:

head -10 myfile <==> cat myfile | select -first 10 tail -10 myfile <==> cat myfile | select -last 10 

But if I want to list all lines except the last three or all lines except the first three, how do you do that? In Unix, I could do "head -n-3" or "tail -n+4". It is not obvious how this should be done for PowerShell.

Answer 1

Useful information is spread across other answers here, but I think it is useful to have a concise summary:

All lines except the first three

1..10 | Select-Object -skip 3 returns (one per line): 4 5 6 7 8 9 10 

All lines except the last three

1..10 | Select-Object -skip 3 -last 10 returns (one per line): 1 2 3 4 5 6 7 

That is, you can do it with built-in PowerShell commands, but there's that annoyance of having to specify the size going in. A simple workaround is to just use a constant larger than any possible input and you will not need to know the size a priori:

1..10 | Select-Object -skip 3 -last 10000000 returns (one per line): 1 2 3 4 5 6 7 

A cleaner syntax is to use, as Keith Hill suggested, the Skip-Object cmdlet from PowerShell Community Extensions (the Skip-Last function in Goyuix's answer performs equivalently but using PSCX saves you from having to maintain the code):

1..10 | Skip-Object -last 3 returns (one per line): 1 2 3 4 5 6 7 

First three lines

1..10 | Select-Object –first 3 returns (one per line): 1 2 3 

Last three lines

1..10 | Select-Object –last 3 returns (one per line): 8 9 10 

Middle four lines

(This works because the -skip is processed before the -first, regardless of the order of parameters in the invocation.)

1..10 | Select-Object -skip 3 -first 4 returns (one per line): 4 5 6 7 

Answer 2

Like the -First and -Last parameters, there is also a -Skip parameter that will help. It is worth noting that -Skip is 1 based, not zero.

# this will skip the first three lines of the text file cat myfile | select -skip 3 

I am not sure PowerShell has something that gives you back everything except the last n lines pre-built. If you know the length you could just subtract n from the line count and use the -First parameter from select. You could also use a buffer that only passes lines through when it is filled.

function Skip-Last {   param (     [Parameter(Mandatory=$true,ValueFromPipeline=$true)][PsObject]$InputObject,     [Parameter(Mandatory=$true)][int]$Count   )    begin {     $buf = New-Object 'System.Collections.Generic.Queue[string]'   }    process {     if ($buf.Count -eq $Count) { $buf.Dequeue() }     $buf.Enqueue($InputObject)   } } 

As a demo:

# this would display the entire file except the last five lines cat myfile | Skip-Last -count 5