compress already replaces the file with the compressed one.
man compress says
Code:
Compress reduces the size of the named files using adaptive Lempel-Ziv
coding. Whenever possible, each file is replaced by one with the
extension .Z, while keeping the same ownership modes, access and modification times.
I've noticed bzip2 gives a little bit better compression than gzip. So...I'm curious...what's gives the best compression out of all the compression utilities?
Thanks! (6 Replies)
I have heard that bz2 compression a relatively new compression encoding algorithm, far superior to tar and gz. I also remember that I downloaded a FreeBSD LiveCD a while back that was only a couple hundred megs instead of the usual 650ish using bz2 - big difference, I'd say. But to the point, what... (4 Replies)
Hi everybody,
Does anybody know,whether linux-2.4.20-8 supports predictor1 compression in PPP protocol support,as i was able to see there were only two compression techniques that r being supported i.e bsd and
deflate compression from "make menuconfig" under network device... (0 Replies)
Hello,
I have a .z file which i understand to be UNIX.
I'm on PC (no UNIX boxes) and have tried many different unzipping programs to extract this .z file, but only PicoZip has allowed me to view what is inside (telling me, i think, that it's not corrupt), but i have not been able to extract... (3 Replies)
Hi Folks,
As I am familiar wih both types compresion forms: gun-zip and .rpm. My questions is how do I uncompress gunz.zip type? As the .rpm I can double click and it will extract...Can someone shed some light on this and thank you...
M (2 Replies)
Hi all,
I am having few files which needs to be concted into a single file and then it is compressed and FTPed from the UNIX server to the Windows server.
For the above purpose i am using gzip command to compress the files after concetenation.
And i am FTP ing the compressed file in the... (3 Replies)
Hello everyone
I want to use compression in my tape when I backup some file. For example I have several files that use 50gb. If I backup this I need to use two cartridge because without compression I can backup 36gb.
My question is with flag I need to use to compress and I can use 72gb in... (2 Replies)
I'am looking for script (or tool) that would compress all files with given extension in all subdirectory. Important part is that every one file have to end in separate archive whit it's own name.
Eaven if I could point multiple file in one directory and compress them it would be ok.
I' am... (1 Reply)
Hi all,
I am working on a sample backup code, where i read the files per 7200 bytes and send it to server. Before sending to server, i compress each 7200 bytes using zlib compression algorithm using dictionary max length of 1.5 MB . I find zlib is slow.
Can anyone recommend me a... (3 Replies)
Hi ,
1-I need to know please if it's possible to compress using openssl?
Here is the version used:
openssl version -a
OpenSSL 0.9.7d 17 Mar 2004 (+ security fixes for: CVE-2005-2969 CVE-2006-2937 CVE-2006-2940 CVE2006-3738 CVE-2006-4339 CVE-2006-4343 CVE-2007-5135 CVE-2008-5077... (3 Replies)
Discussion started by: Eman_in_forum
3 Replies
LEARN ABOUT NETBSD
uncompress
COMPRESS(1) BSD General Commands Manual COMPRESS(1)NAME
compress, uncompress -- compress and expand data
SYNOPSIS
compress [-cdfv] [-b bits] [file ...]
uncompress [-cdfv] [file ...]
DESCRIPTION
compress reduces the size of the named files using adaptive Lempel-Ziv coding. Each file is renamed to the same name plus the extension
``.Z''. As many of the modification time, access time, file flags, file mode, user ID, and group ID as allowed by permissions are retained
in the new file. If compression would not reduce the size of a file, the file is ignored.
uncompress restores the compressed files to their original form, renaming the files by deleting the ``.Z'' extension.
If renaming the files would cause files to be overwritten and the standard input device is a terminal, the user is prompted (on the standard
error output) for confirmation. If prompting is not possible or confirmation is not received, the files are not overwritten.
If no files are specified, the standard input is compressed or uncompressed to the standard output. If either the input and output files are
not regular files, the checks for reduction in size and file overwriting are not performed, the input file is not removed, and the attributes
of the input file are not retained.
The options are as follows:
-b Specify the bits code limit (see below).
-c Compressed or uncompressed output is written to the standard output. No files are modified.
-d Force decompression.
-f Force compression of file, even if it is not actually reduced in size. Additionally, files are overwritten without prompting for
confirmation.
-v Print the percentage reduction of each file.
compress uses a modified Lempel-Ziv algorithm. Common substrings in the file are first replaced by 9-bit codes 257 and up. When code 512 is
reached, the algorithm switches to 10-bit codes and continues to use more bits until the limit specified by the -b flag is reached (the
default is 16). Bits must be between 9 and 16.
After the bits limit is reached, compress periodically checks the compression ratio. If it is increasing, compress continues to use the
existing code dictionary. However, if the compression ratio decreases, compress discards the table of substrings and rebuilds it from
scratch. This allows the algorithm to adapt to the next "block" of the file.
The -b flag is omitted for uncompress since the bits parameter specified during compression is encoded within the output, along with a magic
number to ensure that neither decompression of random data nor recompression of compressed data is attempted.
The amount of compression obtained depends on the size of the input, the number of bits per code, and the distribution of common substrings.
Typically, text such as source code or English is reduced by 50-60%. Compression is generally much better than that achieved by Huffman cod-
ing (as used in the historical command pack), or adaptive Huffman coding (as used in the historical command compact), and takes less time to
compute.
The compress utility exits 0 on success, and >0 if an error occurs.
SEE ALSO zcat(1)
Welch, Terry A., "A Technique for High Performance Data Compression", IEEE Computer, 17:6, pp. 8-19, June, 1984.
HISTORY
The compress command appeared in 4.3BSD.
BSD January 23, 2003 BSD