If you regularly download or look at the functions and scripts I post here, you'll notice I often use Write-Verbose to indicate what is happening. This comes in handy for troubleshooting. But often it would also be helpful to record as a log file of script activity. Unfortunately, you can't pipe Write-Verbose to Out-File. So I came up with my own function called Write-Log that gives me the best of both worlds. I can get verbose messages and send those messages to a text file for logging.<\/p>\n
The function is relatively simple. This is the core code without the comment based help.<\/p>\n
Function Write-Log {\r\n [cmdletbinding()]\r\n\r\n Param(\r\n [Parameter(Position=0)]\r\n [ValidateNotNullOrEmpty()]\r\n [string]$Message,\r\n [Parameter(Position=1)]\r\n [string]$Path=\"$env:temp\\PowerShellLog.txt\"\r\n )\r\n \r\n #Pass on the message to Write-Verbose if -Verbose was detected\r\n Write-Verbose $Message\r\n \r\n #only write to the log file if the $LoggingPreference variable is set to Continue\r\n if ($LoggingPreference -eq \"Continue\")\r\n {\r\n \r\n #if a $loggingFilePreference variable is found in the scope\r\n #hierarchy then use that value for the file, otherwise use the default\r\n #$path\r\n if ($loggingFilePreference)\r\n {\r\n $LogFile=$loggingFilePreference\r\n }\r\n else\r\n {\r\n $LogFile=$Path\r\n }\r\n \r\n Write-Output \"$(Get-Date) $Message\" | Out-File -FilePath $LogFile -Append\r\n }\r\n\r\n} #end function\r\n<\/pre>\nThe function takes two parameters, -Message and -Path. The former is the string of text you want to display and\/or log to a text file. The Path is the filename and path of the log file. I've given this parameter a default value of $env:temp\\PowerShellLog.txt. The function writes the message string to the log file with the current date and time prepended.<\/p>\n
Write-Output \"$(Get-Date) $Message\" | Out-File -FilePath $LogFile -Append<\/pre>\nOutput is always appended to the log file. Because the function uses cmdlet binding, if it detects -Verbose then the Write-Verbose message will be visible.<\/p>\n
#Pass on the message to Write-Verbose if -Verbose was detected\r\nWrite-Verbose -Message $Message\r\n<\/pre>\nNow here's the fun part. I wanted to make Write-Log to behave like Write-Verbose. That is, I wanted to include the command in my scripts and functions but only have it actually do something when I needed it. My Write-Log function looks for two variables. The first is $LoggingPreference. If this has a value of \"Continue\", then logging takes place. I also reference another variable called $loggingFilePreference. This variable contains the filename and path for your log file and takes precedence over the temp file default.<\/p>\n
#only write to the log file if the $LoggingPreference variable is set to Continue\r\n if ($LoggingPreference -eq \"Continue\")\r\n {\r\n \r\n #if a $loggingFilePreference variable is found in the scope\r\n #hierarchy then use that value for the file, otherwise use the default\r\n #$path\r\n if ($loggingFilePreference)\r\n {\r\n $LogFile=$loggingFilePreference\r\n }\r\n else\r\n {\r\n $LogFile=$Path\r\n }\r\n \r\n Write-Output \"$(Get-Date) $Message\" | Out-File -FilePath $LogFile -Append\r\n }\r\n<\/pre>\nThere are several ways then that you could use this. First off, you need to dot source the function either in your PowerShell session or your script\/function. Within your code use Write-Log just like you would Write-Verbose. To \"activate\", all you need to do is set $LoggingPreference to \"Continue\" somewhere. Here's one example.<\/p>\n
Function TryMe {\r\n [cmdletbinding()]\r\n Param([string]$computername=$env:computername,\r\n [string]$Log\r\n )\r\n if ($log) \r\n {\r\n $loggingPreference=\"Continue\"\r\n $loggingFilePreference=$log\r\n }\r\n Write-log \"Starting Command\"\r\n Write-log \"Connecting to $computername\"\r\n $b= get-wmiobject -class win32_bios -ComputerName $computername\r\n $b\r\n Write-log $b.version\r\n Write-Log \"finished\" $log\r\n}\r\n\r\nPS C:\\> TryMe -log e:\\logs\\sample.txt -verbose\r\n<\/pre>\nMy TryMe function includes a parameter called -Log. If I use this parameter, then the logging variables are set and my Write-Log commands will work. If I don't use -Log, Write-Log is still called but nothing is written. Because TryMe uses cmdlet binding, if I run it with -Verbose then I'll get the verbose message via Write-Log. You can even use both -Verbose and -Log which will give you verbose messages and write to the log file. <\/p>\n
Another way would be to turn on the logging variable and use the default log. Here's a snippet.<\/p>\n
Function Test-Foo {\r\n\r\n[cmdletBinding()]\r\n\r\nParam([string]$name,\r\n [switch]$Logging\r\n)\r\n\r\nif ($Logging)\r\n{\r\n $loggingPreference=\"Continue\"\r\n}\r\n\r\nWrite-Log \"Starting Test-Foo\"\r\n...\r\n}\r\n<\/pre>\nThis gives me the -Logging parameter that turns everything on. Remember, in this snippet the log file will the default in the TEMP folder. Although as an added bonus because you can specify a log file, you can write to multiple log files within the same script or function.<\/p>\n
I hope you'll let me know what you think and if you find this useful. If so, don't forget my tip jar.<\/p>\n