If you don't want to match against word boundries \b, then remove those constraints from the regex. ie. 
s/$old_hostname/$new_hostname/sgi

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Note: You may also want to add \Q and \E around your $old_hostname if you don't want any special regex characters in there to affect the match. 

s/\Q$old_hostname\E/$new_hostname/sgi

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In reply to Re: String substitution by Paladin
in thread String substitution by kirk123

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