/Out (devenv.exe) 

FileName

Required. The path and name of the file to receive errors when you build an executable.

If a file name that does not exist is specified, the file is created automatically. If the file already exists, the contents are deleted before running the current build.

Command line build errors are displayed in the Command window and the Solution Builder view of the Output window. This option is useful if you are running unattended builds and need to see the results.

This example runs MySolution and writes errors to the file MyErrorLog.txt.

devenv /run "C:\Documents and Settings\someuser\My Documents\Visual Studio\Projects\MySolution\MySolution.sln" /out "C:\MyErrorLog.txt"

Reference