A better, and more complete way than the OLE version above, is using Image::ExifTool's ImageInfo. This also identifies the new Office file formats with or without extensions:

    #!/usr/bin/perl

    use strict;
    use warnings;
    use Image::ExifTool 'ImageInfo';

    my @files = (

        'test.xls', 'test.xlsx',
        'test.doc', 'test.docx',
        'test.ppt', 'test.pptx',

    );


    for my $filename ( @files ) {

        my $info = ImageInfo( $filename );

        printf( "%-20s = %s\n", $filename, $info->{FileType} );

    }

    __END__
        Output:

        $ perl exif_check.pl
        test.xls             = XLS
        test.xlsx            = XLSX
        test.doc             = DOC
        test.docx            = DOCX
        test.ppt             = PPT
        test.pptx            = PPTX
[download]

It might seem a little odd using Image::ExifTool for this but it has a large number of recognised formats.

--
John.