Be careful about using something like this:

my @matches = ($string =~ /!#(.*?)#!/g);
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That will probably not work the way you want it to on the following:

"123!#45!#678#!90"
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You probably wanted 678, but you get 45!#678 instead. Try something like the following:

my @matches = ($string =~ /!#((?:[^#!]|#(?!!))*)#!/g );
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See this node for details on this.