Editing Web.Config Files with PowerShell

July 29, 2008 at 11:07 PMAndy Schneider

A couple days ago, a colleague of mine (who is a recent PowerShell convert) asked me if there was some cool way in PowerShell to update a web.config file based on the particular environment that the app was being deployed to (dev, test, or production)

I went in to this knowing config files are just XML files and I also knew that PowerShell can do some pretty cool work with XML and I figured there must be a way.

I found a great article called Deployment made simple using Powershell by Omar Al Zabir up on Code Project.

He has a script that does a number of things, but what I was particular interested in was changing the database connection string in a web.config file.

Luckily, Omar had the answer.

I tweaked it a bit and came up with the following:

   1: #Code to update a connection string on a web.config file –yes this can be used to change a lot more stuff too J
   2:  
   3: #Set the Connection String and the path to web.config (or any config file for that matter)
   4: $connectionString = "Data Source=old-db;Initial Catalog=mydb;Integrated Security=True;User Instance=True"
   5: $webConfigPath = "C:\Inetpub\wwwroot\myapp\web.config"
   6: $currentDate = (get-date).tostring("mm_dd_yyyy-hh_mm_s") # month_day_year - hours_mins_seconds
   7: $backup = $webConfigPath + "_$currentDate"
   8:  
   9: # Get the content of the config file and cast it to XML and save a backup copy labeled .bak followed by the date
  10: $xml = [xml](get-content $webConfigPath)
  11:  
  12: #save a backup copy
  13: $xml.Save($backup)
  14:  
  15: #this was the trick I had been looking for
  16: $root = $xml.get_DocumentElement();
  17:  
  18: #Change the Connection String. Add really means "replace"
  19: $root.connectionStrings.add.connectionString = $connectionString
  20:  
  21: # Save it
  22: $xml.Save($webConfigPath)

The one thing I added was the backup copy by saving the current file with the current date and time appended to the end of the file name.

So next time you are tempted to edit a config file with notepad, open up the shell and take a whack at it.

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Comments (5) -

Good article.

Backing up a step from deployment, you might also want to use PowerShell to get your code out of version control and build it. See this CodeProject article:
www.codeproject.com/.../ExtractAndBuild.aspx

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Nice one (you too John)!

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What would be cool would be to have all the keys you want changed in a "ToBeUpdatedWebConfig.config" file that is passed as input... and then all the changed keys in there are read and then merged into the target web.config file.

More flexible that having the keys hard coded as per the (great!) example above.

Now if only I would script...

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Helpful. thanks

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Brian Warner says:

One tiny correction for anyone trying to use your code:
(get-date).tostring("mm_dd_yyyy-hh_mm_s") will give you "Minutes, Days, Year-Hours, Minutes, Seconds"
(get-date).tostring("MM_dd_yyyy-hh_mm_s") will give you "Months, Days, Year-Hours, Minutes, Seconds"

Took me a bit to figure out, not nearly as much time as the code saved, so I still owe you...

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