Unix - useful command line tools

This post lists unix command line tools which are very helpful during a work with these systems.

alias create alias for a command

// use aliast to a command
alias ls='ls -ltr'

awk

// split text into tokens using '.' separator
echo testFile.txt | awk -F'.' '{print$2}' // prints 'txt'

chmod set access privileges to a file

// owner rwx, group r-x, others ---
chmod 750 fileName.txt

Meaning of numbers: owner, group, others (respectively)
4 - read
2 - write
1 - execute

find search for files

// search for all files in a current directory and display lines with a 'stringToFind'
find . -name "*.*" | xargs grep 'stringToFind'

// search for a file and skipp all info about errors
find . -name 'testFile.txt' 2> /dev/null

grep use regexp to display lines from a file

// display all lines without a # sign 
grep ^[^#] testFile.txt

// display all lines with a # sign
grep ^# testFile.txt

gzip compress and decompress files

// display all content of an archive as a file
gzip -cd file.tar.gz | less

head display top lines of a stream or a file (default 10)

// display first 10 lines of a file
head testFile.txt

// display 15 lines of a file
head -n15 testFile.txt

// display 3 head lines of *.txt from a current directory and show their file names
head -n3 *.txt

// display 3 head lines from *.txt from a current directory without file names
head -q -n3 *.txt // -q  means quiet mode

host DNS lookup utility

//get hostname based on IP
$ host 192.168.0.10

kill kill processes

// kill process with a specified PID
kill -9 PID

// kill all user processes
kill -11 -1

less

// display specified file
less testFile.txt

mv move files and folders

mv path/testFile.txt path2

nslookup DNS lookup utility

//get IP based on hostname  
nslookup localhost 

ps display processes of an operation system

// display processes of a current user
ps -fu userName

// 10 most memory-consuming processes
ps -o "pid vsz rssize" -fu ilink | sort -n -r -k 2 | head -20

scp copy files between remote locations over SSH

// copy files to a remote location to a remote location
scp /export/home/* user@host:/export/home/

// copy directories with files
scp -r /path/* user@host:/path/

sed process text streams

// display a text from a middle of a file from a line in a range
sed -n '15,20p' testFile.txt

source send commands from a file to shell

// send commands from a .bashrc file to shell
source .bashrc

tail display bottom lines from a stream or a file (default 10)

//opposite version of head

tar archive files

// tar (zip) a content of a directory into tar.gz file
tar -pczf web.tar.gz web/

// untar(unzip)
tar xvfz web.tar.gz

telnet connect by telnet protocol

// conect to a remote location
telnet host port

Exiting telnet: 
Ctrl + ] (escape character)
Ctrl + d (close conection)

touch change a date of a file modification to a current one or create new file if not exists

touch testFile.txt

uniq return only unique lines

less testFile | uniq 

wc word count

// count lines
cat testFile.txt | grep 'toSearchString' | wc -l

// count words
cat testFile.txt | grep 'toSearchString' | wc -w