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On Mon, Feb 21, 2022 at 8:29 PM Grant Edwards<grant.b.edwards@×××××.com> wrote: |
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> I've got a "raw" USB flash drive containing a large chunk of gzipped |
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> data. By "raw" I mean no partition table, now filesystem. Think of it |
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> as a tape (if you're old enough). |
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> |
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> gzip -tv is quite happy to validate the data and says it's OK, though |
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> it says it ignored extra bytes after the end of the "file". |
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> |
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> The flash drive size is 128GB, but the gzipped data is only maybe |
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> 20-30GB. |
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> |
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> Question: is there a simple way to copy just the 'gzip' data from the |
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> drive without copying the extra bytes after the end of the 'gzip' |
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> data? |
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> |
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> The only thing I can think of is: |
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> |
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> $ zcat /dev/sdX | gzip -c > data.gz |
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> |
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> But I was trying to figure out a way to do it without uncompressing |
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> and recompressing the data. I had hoped that the gzip header would |
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> contain a "length" field (so I would know how many bytes to copy using |
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> dd), but it does not. Apparently, the only way to find the end of the |
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> compressed data is to parse it using the proper algorithm (deflate, in |
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> this case). |
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> |
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> -- |
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> Grant |
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|
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Hi Grant, |
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you could use gzip to tell you the compressed size of the file and then |
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use another method to copy just those bytes (dd for example): |
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gzip -clt </dev/sdX |
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Should print the compressed size in bytes, although by reading through |
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the entire stream once. |
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-- |
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Felix |
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