Find out whether a file is a symbolic link in PowerShell

Question

I am having a PowerShell script which is walking a directory tree, and sometimes I have auxiliary files hardlinked there which should not be processed. Is there an easy way of finding out whether a file (that is, System.IO.FileInfo) is a hard link or not?

If not, would it be easier with symbolic links (symlinks)?

Answer 1

Try this:

function Test-ReparsePoint([string]$path) {
  $file = Get-Item $path -Force -ea SilentlyContinue
  return [bool]($file.Attributes -band [IO.FileAttributes]::ReparsePoint)
}

It is a pretty minimal implementation, but it should do the trick. Note that this doesn't distinguish between a hard link and a symbolic link. Underneath, they both just take advantage of NTFS reparse points, IIRC.

Answer 2

If you have Powershell 5+ the following one-liner recursively lists all file hardlinks, directory junctions and symbolic links and their targets starting from d:\Temp\:

dir 'd:\Temp' -recurse -force | ?{$_.LinkType} | select FullName,LinkType,Target

Output:

FullName                                LinkType     Target
--------                                --------     ------
D:\Temp\MyJunctionDir                   Junction     {D:\exp\junction_target_dir}
D:\Temp\MySymLinkDir                    SymbolicLink {D:\exp\symlink_target_dir}
D:\Temp\MyHardLinkFile.txt              HardLink     {D:\temp\MyHardLinkFile2.txt, D:\exp\hlink_target.xml}
D:\Temp\MyHardLinkFile2.txt             HardLink     {D:\temp\MyHardLinkFile.txt, D:\exp\hlink_target.xml}
D:\Temp\MySymLinkFile.txt               SymbolicLink {D:\exp\symlink_target.xml}
D:\Temp\MySymLinkDir\MySymLinkFile2.txt SymbolicLink {D:\temp\normal file.txt}

If you care about multiple targets for hardlinks use this variation which lists targets tab-separated:

dir 'd:\Temp' -recurse -force | ?{$_.LinkType} | select FullName,LinkType,@{ Name = "Targets"; Expression={$_.Target -join "`t"} }

You may need administrator privileges to run this script on say C:\.

Answer 3

Utilize Where-Object to search for the ReparsePoint file attribute.

Get-ChildItem | Where-Object { $_.Attributes -match "ReparsePoint" }

Answer 4

My results on Vista, using Keith Hill's powershell script to test symlinks and hardlinks:

c:\markus\other>mklink symlink.doc \temp\2006rsltns.doc
symbolic link created for symlink.doc <<===>> \temp\2006rsltns.doc

c:\markus\other>fsutil hardlink create HARDLINK.doc  \temp\2006rsltns.doc
Hardlink created for c:\markus\other\HARDLINK.doc <<===>> c:\temp\2006rsltns.doc

c:\markus\other>dir
 Volume in drive C has no label.
 Volume Serial Number is C8BC-2EBD

 Directory of c:\markus\other

02/12/2010  05:21 PM    <DIR>          .
02/12/2010  05:21 PM    <DIR>          ..
01/10/2006  06:12 PM            25,088 HARDLINK.doc
02/12/2010  05:21 PM    <SYMLINK>      symlink.doc [\temp\2006rsltns.doc]
               2 File(s)         25,088 bytes
               2 Dir(s)   6,805,803,008 bytes free

c:\markus\other>powershell \script\IsSymLink.ps1 HARDLINK.doc
False

c:\\markus\other>powershell \script\IsSymLink.ps1 symlink.doc
True

It shows that symlinks are reparse points, and have the ReparsePoint FileAttribute bit set, while hardlinks do not.

Answer 5

The following PowerShell script will list all the files in a directory or directories with the -recurse switch. It will list the name of the file, whether it is a regular file or a hardlinked file, and the size, separated by colons.

It must be run from the PowerShell command line. It doesn't matter which directory you run it from as that is set in the script.

It uses the fslink utility shipped with Windows and runs that against each file using the hardlink and list switches and counts the lines of output. If two or greater it is a hardlinked file.

You can of course change the directory the search starts from by changing the c:\windows\system in the command. Also, the script simply writes the results to a file, c:\hardlinks.txt. You can change the name or simply delete everything from the > character on and it will output to the screen.

Get-ChildItem -path C:\Windows\system -file -recurse -force | 
    foreach-object {
        if ((fsutil hardlink list $_.fullname).count -ge 2) {
            $_.PSChildname + ":Hardlinked:" + $_.Length
        } else {
            $_.PSChildname + ":RegularFile:" + $_.Length
        }
    } > c:\hardlinks.txt