Dumped pbm file is 0 byte

[zhouhao27]

Here is the sample zpl I used:

^XA

^FX Top section with company logo, name and address.
^CF0,60
^FO50,50^GB100,100,100^FS
^FO75,75^FR^GB100,100,100^FS
^FO88,88^GB50,50,50^FS
^FO220,50^FDInternational Shipping, Inc.^FS
^CF0,40
^FO220,100^FD1000 Shipping Lane^FS
^FO220,135^FDShelbyville TN 38102^FS
^FO220,170^FDUnited States (USA)^FS
^FO50,250^GB700,1,3^FS

^FX Second section with recipient address and permit information.
^CFA,30
^FO50,300^FDJohn Doe^FS
^FO50,340^FD100 Main Street^FS
^FO50,380^FDSpringfield TN 39021^FS
^FO50,420^FDUnited States (USA)^FS
^CFA,15
^FO600,300^GB150,150,3^FS
^FO638,340^FDPermit^FS
^FO638,390^FD123456^FS
^FO50,500^GB700,1,3^FS

^XZ

I used this command:

./ZPL2pbm.pl sample.zpl > dump.pbm

But I got a zero byte dump.pbm. Any idea? Thanks.