is there a way to split a given file whether a text file or image file into smaller chunks of equal size and reassemble them again in python ?
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Is there any way to get the compressed file size in squashfs?
I need to get every single compressed file in squashfs.
This is a list of file sizes that were compressed. They are all originally from \dev\urandom, thus pretty pseudo random. The yellow file is the original size of any and all of them.
The pink files are the compressed sizes, and there are 30 in total. The blue files are the compressed sizes of the pink files once they have been randomly shuffled using Python's shuffle command. The compression algorithms were LZMA, BZ2 and ZLIB respectively from Python's inbuilt modules.
You can see that there are three general blocks of output sizes. Two blocks have a size difference of exactly zero, whilst the other block has randomnesque file size differences as I'd expect due to arbitrary runs and correlations that appear when files as randomly shuffled. BZ2 files have changed by up to 930 bytes. I find it mystifying that LZMA and ZLIB algorithms produced exactly the same filesizes. It's as if there is some code inside specifically looking for no effect.
Q: Why do the BZ2 files significantly change size, whilst shuffling LZMA and ZLIB files has no effect on their compressibility.
I have a large GZIP-ed file. I want to read a few bytes from a specific offset of uncompressed data.
For example, I have a file that original size is 10GB. In gzipped state it has size 1GB. I want to read a few bytes at 5GB offset in that 1GB gzipped file.
You will need to read all of the first 5 GB in order to get just those bytes.
If you are frequently accessing just a few bytes from the same large gzip file, then it can be indexed for more rapid random access. You would read the entire file once to build the index. See zran.h and zran.c.
I have a bunch of small CSV files (a few hundred files about 100 MB each) that I want to pack into several bigger files. I know how to join all (or a subset) of those files into one file - I simply need to use cat command in Linux and redirect its output to a file. My problem is the result files have to be not bigger than some size (say, 5 GB), i.e. merging all small files into one is not a solution because the resulting file will be too big. So, I am wondering if there is a way to do it in the command line that would be simpler than writing a bash script looping over the directory?
Thanks.
The split command does exactly what you need. You can have it split STDIN to different outputs based on size or number of lines. You can also specify the output file suffix.
If a file is not compressed (i.e. stored) in a ZIP file, would its corresponding Central File Header entry have the same compressed and uncompressed sizes? Or is it possible that one of these will be missing?
Yes, it should have both sizes, where compressed size is greater or equal to not-compressed.
It can be greater when encryption is used.