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How to add an entry with a condition to hosts file?

I need to write a script to verify if one specific entry "10.1.17.21  server1" exists in the hosts file or not. If yes, do nothing, else insert that entry into the hosts file.  
This script will be put in the login script to assure all users with this entry in their hosts file.  

Can you help please?
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Castlewood
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Castlewood
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NVITCommented:
findstr /i "10.1.17.21  server1" c:\windows\system32\drivers\etc\hosts

if errorlevel 1 echo "10.1.17.21  server1" >>c:\windows\system32\drivers\etc\hosts

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I don't think you can put it in a users login script because hosts may be protected... Unless user is an admin.

You could put it in a gpo in the Startup script, which should work.
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Bill PrewCommented:
Keep in mind this will need to happen with elevated user permissions on most modern versions of Windows.

~bp
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Bill PrewCommented:
NVIT, I might be overthinking it a bit, I do that, but you might want to make it a bit more robust.  A couple of thoughts that come to mind:

- If for some reason the entry is in the file, but commented out (likely a # on the left part of the line), then we won't add it again, even though we would want to I think.  So perhaps use REGEX for the search and require the IP address to be at the start of the line, preceded only by whitespace.

- Using REGEX, you could handle multiple spaces other than what is assumed between the IP and host name.

- It's possible that we could add the same host name twice to the file, with different IPs, using this approach, but that risk seems too low to code for.  I think Windows would just pick the first matching host name in the file and ignore the second.

~bp
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NVITCommented:
Bill,

This seems to work.

findstr /r /b "10.1.17.21 *server1" c:\windows\system32\drivers\etc\hosts
if errorlevel 1 echo 10.1.17.21  server1 >>c:\windows\system32\drivers\etc\hosts

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