Unix tail equivalent command in Windows Powershell

Question

I have to look at the last few lines of a large file (typical size is 500MB-2GB). I am looking for a equivalent of Unix command tail for Windows Powershell. A few alternatives available on are,

http://tailforwin32.sourceforge.net/

and

Get-Content [filename] | Select-Object -Last 10

For me, it is not allowed to use the first alternative, and the second alternative is slow. Does anyone know of an efficient implementation of tail for PowerShell.

Answer 1

I took @hajamie's solution and wrapped it up into a slightly more convenient script wrapper.

I added an option to start from an offset before the end of the file, so you can use the tail-like functionality of reading a certain amount from the end of the file. Note the offset is in bytes, not lines.

There's also an option to continue waiting for more content.

Examples (assuming you save this as TailFile.ps1):

.\TailFile.ps1 -File .\path\to\myfile.log -InitialOffset 1000000
.\TailFile.ps1 -File .\path\to\myfile.log -InitialOffset 1000000 -Follow:$true
.\TailFile.ps1 -File .\path\to\myfile.log -Follow:$true

And here is the script itself...

param (
    [Parameter(Mandatory=$true,HelpMessage="Enter the path to a file to tail")][string]$File = "",
    [Parameter(Mandatory=$true,HelpMessage="Enter the number of bytes from the end of the file")][int]$InitialOffset = 10248,
    [Parameter(Mandatory=$false,HelpMessage="Continuing monitoring the file for new additions?")][boolean]$Follow = $false
)

$ci = get-childitem $File
$fullName = $ci.FullName

$reader = new-object System.IO.StreamReader(New-Object IO.FileStream($fullName, [System.IO.FileMode]::Open, [System.IO.FileAccess]::Read, [IO.FileShare]::ReadWrite))
#start at the end of the file
$lastMaxOffset = $reader.BaseStream.Length - $InitialOffset

while ($true)
{
    #if the file size has not changed, idle
    if ($reader.BaseStream.Length -ge $lastMaxOffset) {
        #seek to the last max offset
        $reader.BaseStream.Seek($lastMaxOffset, [System.IO.SeekOrigin]::Begin) | out-null

        #read out of the file until the EOF
        $line = ""
        while (($line = $reader.ReadLine()) -ne $null) {
            write-output $line
        }

        #update the last max offset
        $lastMaxOffset = $reader.BaseStream.Position
    }

    if($Follow){
        Start-Sleep -m 100
    } else {
        break;
    }
}

Answer 2

I used some of the answers given here but just a heads up that

Get-Content -Path Yourfile.log -Tail 30 -Wait 

will chew up memory after awhile. A colleague left such a "tail" up over the last day and it went up to 800 MB. I don't know if Unix tail behaves the same way (but I doubt it). So it's fine to use for short term applications, but be careful with it.

Answer 3

Very basic, but does what you need without any addon modules or PS version requirements:

while ($true) {Clear-Host; gc E:\test.txt | select -last 3; sleep 2 }

Answer 4

Using Powershell V2 and below, get-content reads the entire file, so it was of no use to me. The following code works for what I needed, though there are likely some issues with character encodings. This is effectively tail -f, but it could be easily modified to get the last x bytes, or last x lines if you want to search backwards for line breaks.

$filename = "\wherever\your\file\is.txt"
$reader = new-object System.IO.StreamReader(New-Object IO.FileStream($filename, [System.IO.FileMode]::Open, [System.IO.FileAccess]::Read, [IO.FileShare]::ReadWrite))
#start at the end of the file
$lastMaxOffset = $reader.BaseStream.Length

while ($true)
{
    Start-Sleep -m 100

    #if the file size has not changed, idle
    if ($reader.BaseStream.Length -eq $lastMaxOffset) {
        continue;
    }

    #seek to the last max offset
    $reader.BaseStream.Seek($lastMaxOffset, [System.IO.SeekOrigin]::Begin) | out-null

    #read out of the file until the EOF
    $line = ""
    while (($line = $reader.ReadLine()) -ne $null) {
        write-output $line
    }

    #update the last max offset
    $lastMaxOffset = $reader.BaseStream.Position
}

I found most of the code to do this here.