Excellent solution as well - I just tested it and it worked out of the box like this:

use FileHandle::Unget;
  
my $fh = FileHandle::Unget->new(\*STDIN)
 or die "Cannot open filehandle: $!";

my $testline = <$fh>;;
$fh->ungets($testline);

print "$.: $testline";

for (my $i = 0; $i < 3; $i++) {
    $testline = <$fh>;
    print "$.: $testline";
}

[download]

Output for "cat xmlfile | ./perscript.pl" is:

1: <?xml version="1.0" encoding="UTF-8"?>
1: <?xml version="1.0" encoding="UTF-8"?>
2: <MFOP>
3:   <Basics>

[download]

Thank you very much! FileHandle::Unget is *the* answer to my original question.

@ikegami: Unfortunately, the install script (Makefile) for IO::Unread fails with error messages, and there seems to be no debian packet for it available in jessie - so I was not able to test this.

In reply to Re^2: peek at STDIN, to determine data type and then pass STDIN to a parser by aral
in thread peek at STDIN, to determine data type and then pass STDIN to a parser by aral

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