Identifying pseudo-duplicates with Perl - regex

Question

I have a list that contains names. There are multiples of the same name. I want to catch the first instance of these pseudo-dupes and anchor them.
Example input
Josh Smith
Josh Smith0928340938
Josh Smith and friends
hello
hello1223
hello and goodbye.
What I want to do is identify the first occurrence of Josh Smith or hello and put an anchor such as a pipe | in front of it to validate. These are also wildcards as the list is large, so I cannot specifically look for the first match of Josh Smith and so on.
My desired output would be this:
|Josh Smith
Josh Smith0928340938
Josh Smith and friends
|hello
hello1223
hello and goodbye.
I did not provide any code. I am a little in the dark on how to go about this and was hoping maybe someone had been in a similar situation using regex or Perl.

Answer 1

I think based on what I understand of your requirements you are looking for something like this:
$prefix = '';
$buffered = '';
$count = 0;
while ($line = <>) {
$linePrefix = substr($line,0,length($prefix));
if ($buffered ne '' && $linePrefix eq $prefix) {
$buffered .= $line;
$count++;
} else {
if ($buffered ne '') {
print "|" if ($count > 1);
print $buffered;
}
$buffered = $line;
$prefix = $line;
chomp $prefix;
$count = 1;
}
}
if ($buffered ne '') {
if ($count > 1) {
print "|";
}
print $buffered;
}

Answer 2

Actually, IMO this is a rather interesting question, because you can be creative. As you do not know how to identify the root name, I have to ask if you have to? I have a feeling that you do not need a perfect solution. Therefore, I would go for something simple:
#!/usr/bin/perl -wn
$N = 4;
if (#prev) {
$same_start = length $_ >= $N &&
substr($prev[0], 0, $N) eq substr($_, 0, $N);
unless ($same_start) {
print "|", shift #prev if $#prev;
#prev = grep { print;0 } #prev;
}
}
push #prev, $_;
}{ print for #prev
edit: fixed bug: <print "|", shift #prev;> to <print "|", shift #prev if $#prev;>
Sample output:
$ perl josh.pl <josh-input.txt
|Josh Smith
Josh Smith0928340938
Josh Smith and friends
|hello
hello1223
hello and goodbye.