Ah, that's what I was going to say!

So here's something a little different:

local $" = ';';
system qq( sed '@{[ map "s/\\<$_\\>/$_ ($acronyms{$_})/g", keys %acron
+yms ]}' );
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Of course, if the acronym list is long, the above will smack into the command line length limit; in that case, it's easy enough to write a sed script file.