Depending on what you want to do with your 'raw' filehandle, then using: 

 open(my $fh, '<', $filename);
 binmode($fh);

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...may not be appropriate (at least on windows).

If you want to read raw bytes from a filehandle (for example to look for a BOM) and _then_ add an encoding layer then you need to ensure that there isn't a :crlf layer hanging around to begin with which the above has (it may not be enabled, but it's still there *). This is because of :crlf not working nicely with encodings eg. it breaks tell().

So, the method i use is: 

open(my $fh, "<:raw:perlio", $file);

# read first few bytes for a BOM or ASCII in utf(16|32)
#  to determine encoding

binmode $fh, ":encoding($encoding)"

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* Consider: 
open $fh, "<", $^X or die;
binmode $fh;
print "1: ", join(' ', PerlIO::get_layers($fh, details => 1)), "\n";
close $fh;

open $fh, "<:raw:perlio", $^X or die;
print "2: ", join(' ', PerlIO::get_layers($fh, details => 1)), "\n";
close $fh;

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gives: 

1: unix  4195328 crlf  4195328
2: unix  4195328 perlio  4195328

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In reply to Re^2: Using ":raw" layer in open() vs. calling binmode() by Anonymous Monk
in thread Using ":raw" layer in open() vs. calling binmode() by Anonymous Monk

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