Compress (trim) a file from the beginning on linux

Question

Is it possible in Linux (and / or in another Unix) to compress a file from the very beginning? I would like to use it for a constant queue (no existing implementation meets my needs). From the end of the file, I assume this is possible with truncate ().

Answer 1

If you are using ext4, xfs or some other modern file system starting with Linux Kernel 3.15, you can use:

#include <fcntl.h> int fallocate(int fd, int mode, off_t offset, off_t len); 

with the flag FALLOC_FL_COLLAPSE_RANGE .

http://manpages.ubuntu.com/manpages/disco/en/man2/fallocate.2.html

Answer 2

Yes, you can use cut or tail to delete parts of the file.

cut -b 17- input_file
tail -c +17 input_file

This outputs the contents of the input file starting at the 17th byte, effectively deleting the first 16 bytes of the file. Note that the cut example will also add a new line for output.

Answer 3

I have a truncated file specified as an argument of 64,000,000 bytes using the following Python script:

 #!/usr/bin/env python import sys import os file = sys.argv[1] f = os.open(file, os.O_RDWR) os.ftruncate(f, 64000000) os.close(f)