Welcome to PerlMonks!, santoshkumarcp

It will be easier for people to help you if you surround your code (e.g. the part after My code is like this...) with <code>...</code> tags. This will make your code look more like it looks when you type it into the input box. If you can't see the edit box, scroll down a bit in your browser window. If you still can't see it, click on the title of your post.

As for the question itself: you can use the concatenation (dot) operator 'IP_' . $newHosts->{server} to get the sting "IP_10.100.200.10". Further discussion aimed at a beginner can be found at How to concatenate stings with Perl.

Best, beth

Please use code tag, for posting the code.

You can use dot (.) operator for concatenate the strings in Perl.

s/^(?=\d+\.\d+\.\d+\.\d+)/IP_/ for values %{ $newHosts->{ server } };
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Hmmm ,

The OP would like the existing IP address prefixed with i.e. not replaced by, the string 'IP_', viz:

s/^/IP_/ for values %{ $newHosts->{ server } };
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or

$_ = q/IP_/ . $_ for values %{ $newHosts->{ server } };
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A user level that continues to overstate my experience :-))

jwkrahn's code is not doing a replacement because his pattern is inside a zero-width positive look-ahead assertion, i.e. it is in effect doing an insertion at a point in the string that is followed by the pattern because the item being substituted is zero-width.

Cheers,

JohnGG