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.

Solution 1

Use the -wait parameter with Get-Content, which displays lines as they are added to the file. This feature was present in PowerShell v1, but for some reason not documented well in v2.

Here is an example

Get-Content -Path "C:\scripts\test.txt" -Wait

Once you run this, update and save the file and you will see the changes on the console.

Solution 2

For completeness I'll mention that Powershell 3.0 now has a -Tail flag on Get-Content

Get-Content ./log.log -Tail 10

gets the last 10 lines of the file

Get-Content ./log.log -Wait -Tail 10

gets the last 10 lines of the file and waits for more

Also, for those *nix users, note that most systems alias cat to Get-Content, so this usually works

cat ./log.log -Tail 10

Solution 3

As of PowerShell version 3.0, the Get-Content cmdlet has a -Tail parameter that should help. See the technet library online help for Get-Content.

Solution 4

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.

Solution 5

PowerShell Community Extensions (PSCX) provides the Get-FileTail cmdlet. It looks like a suitable solution for the task. Note: I did not try it with extremely large files but the description says it efficiently tails the contents and it is designed for large log files.

NAME
    Get-FileTail

SYNOPSIS
    PSCX Cmdlet: Tails the contents of a file - optionally waiting on new content.

SYNTAX
    Get-FileTail [-Path] <String[]> [-Count <Int32>] [-Encoding <EncodingParameter>] [-LineTerminator <String>] [-Wait] [<CommonParameters>]

    Get-FileTail [-LiteralPath] <String[]> [-Count <Int32>] [-Encoding <EncodingParameter>] [-LineTerminator <String>] [-Wait] [<CommonParameters>]

DESCRIPTION
    This implentation efficiently tails the cotents of a file by reading lines from the end rather then processing the entire file. This behavior is crucial for ef
    ficiently tailing large log files and large log files over a network.  You can also specify the Wait parameter to have the cmdlet wait and display new content
    as it is written to the file.  Use Ctrl+C to break out of the wait loop.  Note that if an encoding is not specified, the cmdlet will attempt to auto-detect the
     encoding by reading the first character from the file. If no character haven't been written to the file yet, the cmdlet will default to using Unicode encoding
    . You can override this behavior by explicitly specifying the encoding via the Encoding parameter.

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Comments

[Rich]

Interesting. I would have thought that all arguments that exist also appear in help, yet man gc -par wait tells me there is no parameter. But I think this doesn't solve the problem that the OP has, since they asked for tail, not tail -f and an efficient implementation as well. Since this one also reads the complete file before returning the last lines this is painful for the file sizes they expect.

[ravikanth]

Gotcha. May be IO.File has some way to seek to the required position. I will have to experiment a bit

[Rich]

I guess one could implement it as a PowerShell function, using the normal .NET APIs. Seeking to the end, search backwards until the desired number of lines is found and emit them. Not pretty, probably, but might work. I just can't wrap my head around it right now, otherwise I would have started writing already ;-)

[Keith Hill]

There's a bug in the current version that is fixed in daily bits. I would recommend grabbing the latest bits and compiling them at least until we get an updated version released.

[Keith Hill]

FYI, this is what the Get-FileTail (alias tail) implementation does in PSCX. If you're curious you can look at the source code: pscx.codeplex.com/SourceControl/changeset/view/78514#1358075

[mutelogan]

The solution "Get-Content -Path "C:\scripts\test.txt" -Wait" doesn't work well for large files as Joey commented. Thanks for all the suggestions.

[JasonMArcher]

@Joey -Wait is a dynamic parameter that only applies to the FileSystem provider. GC can be used on any provider that implements that API. The only way besides documentation that I know to discover these is to use (gcm Get-Content).Parameters from within the appropriate provider path. Don't use the alias "gc" because the dynamic parameters will not show up.

[Rich]

@Jason: Ah, damn it, I should have known. Yes, makes sense.

[Jader Dias]

The version 2.0 takes ages to show the 10 last lines of a 1GB csv file, and differently from Get-Content [filename] | Select-Object -Last 10 it can't be aborted

[David Newcomb]

I know it was a while ago, but this requires the process writing to the file to open, append, close it before Get-Content will work. If the writing process never closes the file then it won't work which is not the case with tail -f.

[JoshL]

Oddly, -Wait only shows me new lines when I access a log file in some way (such as selecting it in Windows Explorer). Tail provides updates as new lines are written to my file. With -Wait, I can leave a PowerShell window open happily showing no new lines while the file is being written to. If I then pop over and click on the file in Windows Explorer, suddenly PowerShell "wakes up" and catches up the remaining lines. Is this a bug?

[Shagglez]

@JoshL - I noticed the same thing with Epilog, I guess it's using PowerShells under the bonnet.

[Gedrox]

Link to download here – microsoft.com/en-us/download/details.aspx?id=34595.

[tjmoore]

Note for some - PS 3.0 is Unavailable to Windows XP and Vista.

[Abhishek]

@LauraLiparulo in what way does this not work? I've used it before definitely.

[Coops]

I just used it and it worked spot on in this format Get-Content .\test.txt -Wait -Tail 1

[Pecos Bill]

That's brutal on large files.

[Govert]

Is it true that Get-Content with the -Tail option reads the entire file? On large files it seems OK for me.

[hajamie]

I believe it depends on the PS version. I've updated the answer. I was stuck on a server without the ability to install anything at the time, so the above code was useful.

[yankee]

@JoshL: Indeed this does not work like tail -f. See: stackoverflow.com/questions/19919180/…

[underscore_d]

Yeah, this is really not the same. Not only does it not handle persistently opened files as mentioned - it also has to print the entire file before it'll start showing you the changes - which is rather hopeless if you're trying to tail a log file 100s of MB in size.

[elika kohen]

@LauraLiparulo - Works for me also: Get-Content -Path .\sync.log -Wait -Tail 10

[Robotnik]

@JoshL - View the folder in details mode in Explorer - when you click the file, watch the file size. It seems explorer doesn't really 'care' about refreshing the file until you click on it. Interesting that this is happening to PS as well, it must be lower-level than both Explorer and PS.

[Tony Hinkle]

Per the comment of JoshL above, I think this behavior is due to the application caching it's log writes and not flushing them to disk until the file is read. This is a common strategy for making logging more efficient. It certainly makes it a pain, though. You could perhaps work around it by having another script read (part?) of the file periodically...

[Jake Nelson]

I use the technique mentioned by Dan but I record it in my $PROFILE. Open it with notepad $PROFILE. Then in the text document, create a new function: function Tail ($path) { Get-content -tail 15 -path $path -wait } This way you can access the function each time you start PowerShell.

[Teoman shipahi]

On ISE, I used to use while($true)/sleep and switched to this one, but this one also locks entire ISE and cannot run scripts on other tabs. Should I just start a new ISE instance?

[Abhishek]

@Teomanshipahi In whwat way did the -Wait parameter not work for you?

[Teoman shipahi]

@GeorgeMauer conceptually I misunderstood how ISE works. I thought different tabs have their own context, but if one script runs on one tab, I cannot run other scripts on other tabs. I think this is expected behaviour.

[Abdullah Leghari]

This should be the accepted answer. -Wait flag mentioned in currently accepted answer doesn't work anymore.

[NoLifeKing]

My workaround was: while($true) { Clear-Host; Get-Content <filename> -tail 40; sleep 1 } :)

[Robbie Dee]

Great stuff - been trying to find a way to do this for ages. If I'm ever in Bangalore, I'll buy you a beer! :-D

[nyagolova]

Sorry for silly question, but how do you exit the reading? How to tell the wait to stop waiting?

[ravikanth]

CTRL+C should stop wait on the content.

[Robear]

Powershell has an alias for cat, by default. So cat "C:\scripts\test.txt" -Wait would work as well, if you're accustom to the Unix syntax. You can also alter your powershell profile so you can just use the tail command: function tail { cat $args -Wait } will let you do tail "C:\scripts\test.txt". You can find the path to your profile in the $PROFILE variable.

[Nico Nekoru]

Hello. Welcome to SO. Before you answer a question take notice of the 12 other answers, 3 having scores over 100.

[Timo]

Can I tail a command, not a file? Such as history -tail 10?

[Andries]

None of these have a follow options. Which is the 99% use case for using the tail command.

[Jason S]

@Andries did you see Ravikanth's answer? You can use -Wait to follow.

[Admin]

Added the flag suggested by @JasonS