Compress commands (gzip, gunzip, zcat)
gzip compresses a file to reduce the space
needed to store it. This conserves disk space. The compression is
loss-less, meaning that no information is lost in the process.
Companion programs are
gunzip to undo the compression
and restore the file to its original size, and
to let you view the contents of compressed files without having
to uncompress first.
The following sequence of commands checks the size of the file unixpast.txt, the compresses it, checks the size again, output the content of the compressed file to the screen, and finally restore it to its original size.
$ ls -l unixpast.txt -rw-r--r-- 1 john staff 7786 2012-10-15 08:16 unixpast.txt $ gzip unixpast.txt $ ls -l unixpast.txt.gz -rw-r--r-- 1 john staff 3548 2012-10-15 08:16 unixpast.txt.gz $ zcat unixpast.txt.gz … $ gunzip unixpast.txt.gz
Try out all the commands described above on the file unixpast.txt. Make a note of file sizes and compute the compression ratio using the formula:
compression ratio = compressed size / compressed size
If the text scrolls too fast for you when you try out the
zcat command, pipe the output though
Packing and unpacking (tar)
||compress file to reduce file space|
||expand compressed file|
||expand compress file and print it stdout|