If the delimiter is a constant then simply doing a join should work to reverse it.

my $delim = ':TAG:';
my @data = split $delim, $line;
my $line = join $delim, @data;

[download]

If the delimiter varies, ie. is a regexp, then things get more fun, but I'll only think about that if needed.

The other obvious solution is to keep a copy of the original line about, no point rejoining if it's practical to simply throw it back out.

Update: Misunderstood the question somewhat. If you're happy with keeping the tag at the start then a lookahead regexp assertion may be just what you're looking for. Have a look at this. 
my $data = ":TAG:This:TAG:is:TAG:a:TAG:test:TAG:";
my @results = split /(?=:TAG:)/, $data;

[download]

I've not played with these things properly so I have no idea how performant they may be, however.

In reply to Re: Splitting and maintaining the delimiter by Molt
in thread Splitting and maintaining the delimiter by Rich36

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