Using awk to remove the Byte-order mark

Try this:

awk 'NR==1{sub(/^\xef\xbb\xbf/,"")}{print}' INFILE > OUTFILE

On the first record (line), remove the BOM characters. Print every record.

Or slightly shorter, using the knowledge that the default action in awk is to print the record:

awk 'NR==1{sub(/^\xef\xbb\xbf/,"")}1' INFILE > OUTFILE

1 is the shortest condition that always evaluates to true, so each record is printed.

Enjoy!

-- ADDENDUM --

Unicode Byte Order Mark (BOM) FAQ includes the following table listing the exact BOM bytes for each encoding:

Bytes         |  Encoding Form
--------------------------------------
00 00 FE FF   |  UTF-32, big-endian
FF FE 00 00   |  UTF-32, little-endian
FE FF         |  UTF-16, big-endian
FF FE         |  UTF-16, little-endian
EF BB BF      |  UTF-8

Thus, you can see how \xef\xbb\xbf corresponds to EF BB BF UTF-8 BOM bytes from the above table.

Not awk, but simpler:

tail -c +4 UTF8 > UTF8.nobom

To check for BOM:

hd -n 3 UTF8

If BOM is present you'll see: 00000000 ef bb bf ...

I know the question was directed at unix/linux, thought it would be worth to mention a good option for the unix-challenged (on windows, with a UI).
I ran into the same issue on a WordPress project (BOM was causing problems with rss feed and page validation) and I had to look into all the files in a quite big directory tree to find the one that was with BOM. Found an application called Replace Pioneer and in it:

Batch Runner -> Search (to find all the files in the subfolders) -> Replace Template -> Binary remove BOM (there is a ready made search and replace template for this).

It was not the most elegant solution and it did require installing a program, which is a downside. But once I found out what was going around me, it worked like a charm (and found 3 files out of about 2300 that were with BOM).