09-24-2011
Yes in some ways they are the same functionality they intend to compress data.
Some do better than others e.g gzip is better than compress and pack in overall .
compress and gzip are alike in some ways as they are exploit the same algorithm but they differ in some ways.
compress : The compress utility will attempt to reduce the size of the named files by using adaptive Lempel-Ziv coding. Typically, text such as source code or English is reduced by 50-60%. Compression is generally much better than that achieved by Huffman coding (as used in pack ).
pack : The pack command attempts to store the specified files in a compressed form. Wherever possible (and useful), each input file file is replaced by a packed file file.z with the same access modes, access and modified dates, and owner as those of file. If pack is successful, file will be removed.
gzip Is a GNU version of Lempel-Ziv coding (LZ77) which reduces the size of the named files using Lempel-Ziv coding (LZ77). Whenever possible, each file is replaced by one with the extension ‘.gz’, while keeping the same ownership modes, access and modification times.
This User Gave Thanks to h@foorsa.biz For This Post:
10 More Discussions You Might Find Interesting
1. UNIX for Dummies Questions & Answers
I have hundreds of ".Z" files that I need to uncompress and gzip. I'm not sure how to handle this in a 'for loop'. I can get the uncompress part, but I'm not sure how to strip the .Z off the filename for the gzip step. Is it possible to pipe the output of uncompress to gzip? (2 Replies)
Discussion started by: 98_1LE
2 Replies
2. UNIX for Dummies Questions & Answers
hi
i dont can traspassing file from unix sco compress whit pack or compress i dont can descompress whit other program... how i can do descompress that file in windows me.???
thank very much...
pd:sorry my inglish (6 Replies)
Discussion started by: jtapia
6 Replies
3. SCO
Our End of Day backup routine uses following script.
start End-of-day
compress $BASE TO /home/compdir
write /home/compdir to DATTAPE
end
where
$BASE=/home2/Rev83
DATATAPE=/dev/rmt/ctape1
write=cpio (not sure about parameters)
since I'm new to UNIX, i dont know how to restore data... (1 Reply)
Discussion started by: tayyabq8
1 Replies
4. UNIX for Dummies Questions & Answers
I am brand new to unix and am hoping someone can start me in the right direction.
I hope I have the right forum but if not can a moderator move this thread to the right area.
I am moving servers and need to back up a folder and its sub folders into a .tar.gz file then want to upload that file... (2 Replies)
Discussion started by: kushti
2 Replies
5. UNIX for Dummies Questions & Answers
hi can i know the diff between these 2 commands in terms of data compressed (3 Replies)
Discussion started by: anandapani
3 Replies
6. UNIX for Dummies Questions & Answers
I have a file that contains user id and corresponding password.
Lets say password is "help". The below command will create a hex value for string "help".
perl -e 'print unpack "H*","help"'
So now password is in encoded format.
Then I decoded it in the script where am fetching the... (1 Reply)
Discussion started by: max_payne1234
1 Replies
7. UNIX for Dummies Questions & Answers
Duplicate threads merged jmc
Hi,
I have a script wherein I want to use gzip instead of compress.
# cat dly_appsfiles_bkp.ksh
#
# dly_appsfiles_bkp.ksh
#
date_stamp=`date +%m%d%y`
base_dir=/u05/gld1
sub_dir=apps
bkp_dir=/u00/backup/GLD1/APPS... (5 Replies)
Discussion started by: narayanv
5 Replies
8. UNIX for Advanced & Expert Users
Hi,
in AIX 6.1 what is the limite of gzip and compress ?
I mean what can be at most the size of the file to compress ?
Thank you. (1 Reply)
Discussion started by: big123456
1 Replies
9. UNIX for Dummies Questions & Answers
I am using pack/unpack to encyrpt a file.
syntax is below
#!/bin/sh
encrypt=`perl -e 'print unpack "H*","yourpassword"'` -
echo $encrypt >/file/to/store/encrypted/password
pass=`cat /file/to/store/encrypted/password`
decrypt=`perl -e 'print pack "H*",$pass'` ... (2 Replies)
Discussion started by: erinlomo
2 Replies
10. UNIX for Beginners Questions & Answers
Good afternoon friends.
I wanted to make a query, how to compress several files and leave them all in 1, for example
flat text files:
filename_1.csv
filename_2.csv
filename_3.csv
expected result
filename_end.gzip = (filename_1.csv
filename_2.csv
filename_3.csv)
please (2 Replies)
Discussion started by: tricampeon81
2 Replies
LEARN ABOUT ULTRIX
compress
compress(1) General Commands Manual compress(1)
Name
compress, uncompress, zcat - compress and expand data
Syntax
compress [ -f ] [ -v ] [ -c ] [ -b bits ] [ name ... ]
uncompress [ -f ] [ -v ] [ -c ] [ name ... ]
zcat [ name ... ]
Description
The command 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. If no files are specified, the
standard input is compressed to the standard output. Compressed files can be restored to their original form using or
The -f option will force compression of name, even if it does not actually shrink name, or if the corresponding name .Z file
already exists. If the -f option is omitted, the user is asked whether an existing name.Z file should be overwritten (unless is
run in the background under
The -c (cat) option makes compress/uncompress write to the standard output without changing any files. Neither -c nor alter files.
The command uses the 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 (default 16). The bits must be between 9 and 16. The default can be changed in the source to allow to be run on a
smaller machine.
After the bits limit is attained, periodically checks the compression ratio. If the ratio is increasing, continues to use the
existing code dictionary. However, if the compression ratio decreases, discards the table of substrings and rebuilds it from
scratch. This allows the algorithm to adapt to the next block of the file.
Note that the -b flag is omitted for since the bits parameter specified during compression is encoded within the output along with
a number that ensures that neither decompression of random data nor recompression of compressed data is attempted.
How much each file is compressed depends on the size of the input, the number of bits per code, and the distribution of common sub-
strings. Typically, text such as source code or English is reduced by 50-60%. Compression is generally much better than that
achieved by Huffman coding or adaptive Huffman coding, and takes less time to compute.
The -v option displays the percent reduction of each file.
If an error occurs, exit status is 1. However, if the last file was not compressed because it became larger, the status is 2.
Otherwise, the status is 0.
Options
-f Forces compression of name.
-c Makes compress/uncompress write to the standard output.
-b Specifies the allowable bits limit. The default is 16.
-v Displays the percent reduction of each file.
Diagnostics
Usage: compress [-fvc] [-b maxbits] [file ...]
Invalid options were specified on the command line.
Missing maxbits
Maxbits must follow -b.
file: not in compressed format
The file specified to uncompress has not been compressed.
file: compressed with xx bits, can only handle yy bits
The file was compressed by a program that could deal with more bits than the compress code on this machine. Recompress the file
with smaller bits.
file: already has .Z suffix -- no change
The file is assumed to be compressed already. Rename the file and try again.
file already exists; do you wish to overwrite (y or n)?
Type y if you want the output file to be replaced; type n if you do not.
uncompress: corrupt input
A SIGSEGV violation was detected which usually means that the input file is corrupted.
Compression: xx.xx%
Percent of the input saved by compression. (For the -v option only.)
-- not a regular file: unchanged
If the input file is not a regular file (for example, a directory), it remains unchanged.
-- has xx other links: unchanged
The input file has links; it is left unchanged. See for more information.
-- file unchanged
No savings is achieved by compression. The input remains unchanged.
Restrictions
Although compressed files are compatible between machines with large memory, -b12 should be used for file transfer to architectures
with a small process data space (64KB or less).
RISC compress(1)