Compression of Duplicate Lines
In the Unix programs od and hexdump, not all lines of display output that contain the same data as the previous line are shown; instead, a line containing just one asterisk is displayed. For example, a block of all zeros is printed as:
0000000 0000 0000 0000 0000 0000 0000 0000 0000 * 0000030This compression feature makes a useful tool for inspecting large files or complete devices for irregularities. In a modern Linux system, it is convenient to scan an entire hard drive to check if it is all blank:
# hexdump /dev/sda (replace sda with the proper name for the device to be scanned)The -v option causes hexdump and od to display all input data, explicitly:
0000000 0000 0000 0000 0000 0000 0000 0000 0000 0000010 0000 0000 0000 0000 0000 0000 0000 0000 0000020 0000 0000 0000 0000 0000 0000 0000 0000Read more about this topic: Hex Dump
Famous quotes containing the words compression, duplicate and/or lines:
“Do they [the publishers of Murphy] not understand that if the book is slightly obscure it is because it is a compression and that to compress it further can only make it more obscure?”
—Samuel Beckett (1906–1989)
“O Nature, and O soul of man! how far beyond all utterance are your linked analogies! not the smallest atom stirs or lives in matter, but has its cunning duplicate in mind.”
—Herman Melville (1819–1891)
“GOETHE, raised o’er joy and strife,
Drew the firm lines of Fate and Life,
And brought Olympian wisdom down
To court and mar, to gown and town,
Stooping, his finger wrote in clay
The open secret of to-day.”
—Ralph Waldo Emerson (1803–1882)