my $str = "//111.11.112.12/abc/main/myfolder/docs";
my $replace = "something";
$str =~ s#.+(?=/main)#$replace#";
print "str now = $str";
[download]

output:

str now = something/main/myfolder/docs
[download]

davidj

update:Thanks davido for pointing out the error in my response. I guess I need to read the questions a little more closely. Your solution (in addition to being correct :) ) is much better.
davidj