Check out Text::Vpp. It's a flexible preprocessor which handles include statements. That way, you can have statements like:

<P>And here is something from another file:
@INCLUDE other_file.txt
We now return to your regularly scheduled text.
</P>
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That's assuming that you want to use a preformatted template file. Otherwise, a useful shortcut is to use File::Copy:

use File::Copy;

## ...

print STDOUT "<P>And here is something from another file:\n";
copy('other_file.txt', \*STDOUT) or print STDOUT "[Oops: $!]\n";
print STDOUT "We now return you to your regularly scheduled text.\n";
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Theoretically, this might save some memory over reading the entire file into a string.

If you want to keep your HTML separate from your code (which is a worthy goal), then use one of the templating systems mentioned above.

stephen