I tried this: s/^\N{ZERO WIDTH NO-BREAK SPACE}//;

Works for me (unanchored):

#!/usr/bin/env perl 
use strict;
use warnings;
use Test::More tests => 2;

my $src = "foo\x{feff}bar";

my $res = $src;
$res =~ s/\N{ZERO WIDTH NO-BREAK SPACE}//;
isnt ($res, $src, 'Output differs from src');
is ($res, 'foobar', 'BOM stripped');
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You can always add the anchor in if required (as the BOM should only occur at the start as Athanasius explained).