Redhat - Day4 (Basic Linux Commands).txt

//Compression
ls -ldh

-l for long listing
-d for directory
-h for size

Question- How to remove history when you type?

HISTCONTROL=ignorespace

space before each command,command is now on not counted to history

history -d [history_number]

to delete the history of command HISTCONTROL=ignorespace

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Directory by default take 4KB size

du -sh /etc   --------disk usage command to know,summary size in human readable form

DMA-- dynamic memory allocation will give 4KB extra if needed depending upon number of files

directory cannot be compressed but a file specially text file will compressed maximum


likely to use
zip     Gzip   	 bzip2
90%	99%	 99.99%

compression rate

we use yes command to write,redirect output using > to the file

yes hii hii hii hii hii hii hii hii hii hii            > a.txt    20 second maximum

it will create a file,myfile.txt has size of 1.6G

now using two compression

gzip compression first--
gzip -v myfile.txt        ---- (-v) is used to show background process detail graphically,human readable.
takes 48 sec with compression ratio 99.7% and size of compressed file is 4.6M

gunzip decompression
gunzi -v myfile.txt.gz		 is used to decompress file
takes 39 sec to decompress

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bzip2 compression
bzip2 -v myfile.txt   ------size of file is less than 30K


bunzip2 decompression
bunzip2 -v myfile.txt 
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wc -l : Prints the number of lines in a file.
wc -w : prints the number of words in a file.
wc -c : Displays the count of bytes in a file.
wc -m : prints the count of characters from a file.
wc -L : prints only the length of the longest line in a file.