Capturing (failed) mklink command output

Question

Does anybody know why the below happens and does anybody have a workaround?

I'm strugging to capture mklink command output (via cmd.exe mklink > out.txt)

Output is sent to out.txt fine if the mklink command is successful

E.G: %comspec% /c mklink /d C:\Test C:\Windows > out.txt && notepad out.txt

However if the command is invalid, or fails, then nothing will be written to out.txt

E.G: Run above command again (fails because C:\Test already exists) or

E.G: %comspec% /c mklink > out.txt && notepad out.txt

I'm using the command in VBScript, does anybody know how to capture the mklink output if the command isn't completed successfully?

Set o_shell = CreateObject("Wscript.Shell")
Set o_fso = CreateObject("Scripting.FileSystemObject")
mklinkCommandOutput = GetCommandOutput("mklink /D ""C:\Test"" ""C:\Windows""")
WScript.echo mklinkCommandOutput

Function GetCommandOutput(runCmd)
  on error resume next
  Dim o_file, tempFile: tempFile = o_shell.ExpandEnvironmentStrings("%TEMP%") & "\tmpcmd.txt"

  ' Run command and write output to temp file
  o_shell.Run "%COMSPEC% /c " & runCmd & " > """ & tempFile & """", 0, 1

  ' Read command output from temp file
  Set o_file = o_fso.OpenTextFile(tempFile, 1)
  GetCommandOutput = o_file.ReadAll
  o_file.Close

  ' Delete temp file
  Set o_file = o_fso.GetFile(tempFile)
  o_file.Delete
End Function

score 1 · Answer 1 · answered Mar 25 '14 at 16:44

Have you considered utilizing the "Exec" command rather than the run command and collecting the output results?

It doesn't require a file and it's just easier.

New Code

Function GetCommandOutput(runCmd)
  Dim WshShell, oExec
  Set WshShell = CreateObject("WScript.Shell")
  Set oExec    = WshShell.Exec("%COMSPEC% /c " & runCmd)
  GetCommandOutput = oExec.StdOut.ReadAll
End Function

Old Code

Function GetCommandOutput(runCmd)
  on error resume next
  Dim o_file, tempFile: tempFile = o_shell.ExpandEnvironmentStrings("%TEMP%") & "\tmpcmd.txt"

  ' Run command and write output to temp file
  o_shell.Run "%COMSPEC% /c " & runCmd & " > """ & tempFile & """", 0, 1

  ' Read command output from temp file
  Set o_file = o_fso.OpenTextFile(tempFile, 1)
  GetCommandOutput = o_file.ReadAll
  o_file.Close

  ' Delete temp file
  Set o_file = o_fso.GetFile(tempFile)
  o_file.Delete
End Function

I've tried using Exec before, even adding a loop to wait for the command status, but it's always the same result, as if I run this: http://pastebin.com/raw.php?i=axHVLLSz — aciid, Mar 25 '14 at 16:53
Okay `GetCommandOutput = oExec.StdErr.ReadAll` works :) problem solved, sweet — aciid, Mar 25 '14 at 18:21

score 1 · Accepted Answer · answered Mar 25 '14 at 18:26

(1) According to Using multiple commands and conditional processing symbols, the symbol && runs the command on the right only if the command on the left succeeds. You must use & to start notepad even when the mlink fails.

(2) While the mlink docs don't say so explicitly, I assume that mlink writes its error message to Stderr (see here) - just like dir.

Evidence:

dir 01.vbs
...
19.10.2012  11:29             2.588 01.vbs
...
(dir succeeded)

dir nix
...
File Not Found
(dir failed)

dir nix && echo nothing to see, because lefty failed
...
File Not Found
(dir failed, no output because of &&)

dir nix & echo much to see, although lefty failed
...
File Not Found
much to see, although lefty failed
(dir succeeded, echo done because of &)

(3) To capture the output of mlink (rsp. dir) whether it fails or not and to display the result (file) in notepad, you have to use

dir 01.vbs 1> out.txt 2>&1 & notepad out.txt
dir nix 1> out.txt 2>&1 & notepad out.txt

to redirect Stdout and Stderr to the output file.

Evidence:

Dos & Notepads

Just figured that out too - cheers! I was just using && notepad to try and open the output file to show you guys, but thanks again for the tips — aciid, Mar 25 '14 at 18:52
+1 for using commands link. I don't quite understand the Evidence block you use sometimes in your answers. I get it's a real time log of code execution. I just don't see an explanation of that much. — Rich, Mar 26 '14 at 23:11

Capturing (failed) mklink command output

2 Answers2