Unix Commands

Redirecting the Output  

We use the > symbol to redirect the output of a command. For example, to create a file called list1 containing a list of fruit, type  

 cat > list1

Then type in the names of some fruit. Press [Return] after each one.

pear

banana

apple

^D {this means press [Ctrl] and [d] to stop}

Appending to a file

The form >> appends standard output to a file. So to add more items to the file list1, type

cat >> list1

Then type in the names of more fruit

peach

grape

orange

^D (Control D to stop)

To read the contents of the new file, type

ls:- The ls command is a command-line utility for listing the contents of a directory or directories given to it via standard input. It writes results to standard output. The ls command supports showing a variety of information about files, sorting on a range of options and recursive listing.

For help in Unix

man – view manual pages for Unix commands

Unix Shell Commands

clear – clear screen

history – show history of previous commands

more - to display a file, screen by screen;

Time and Date commands

date – show current date and time

sleep – wait for a given number of seconds

uptime – find out how long the system has been up

Unix users commands

These commands allow you to get basic information about Unix users in your environment.

whoami – show your username

id – print user identity

groups – show which groups user belongs to

passwd – change user password

who – find out who is logged into the system

last – show history of logins into the system

Text file operations in Unix

Most of important configuration in Unix is in clear text files, these commands will let you quickly inspect files or view logs:

cat – concatenate files and show contents to the standard output

more – basic pagination when viewing text files or parsing Unix commands output

less – an improved pagination tool for viewing text files (better than more command)

head – show the first 10 lines of text file (you can specify any number of lines)

tail – show the last 10 lines of text file (any number can be specified)

grep – search for patterns in text files

Unix directory management commands

Navigating filesystems and managing directories:

cd – change directory

pwd – confirm current directory

ln – make links and symlinks to files and directories

mkdir – make new directory

rmdir – remove directories in Unix

Unix system status commands

Most useful commands for reviewing hostname configuration and vital stats:

hostname – show or set server hostname

w – display system load, who's logged in and what they are doing

uname – print Unix system information

Networking commands in Unix

Most useful commands for inspecting network setup and exploring network connections and ports:

ifconfig – show and set IP addresses (found almost everywhere)

ip – show and set IP addresses (in recent Linux versions)

ping – check if remote host is reachable via ICMP ping

netstat – show network stats and routing information

Process management

Listing processes and confirming their status, and stopping processes if needed:

ps – list processes

top – show tasks and system status

kill – kill a process (stop application running)

Remote access commands

ssh is really the only way to go, but it's important to know telnet as well:

telnet – clear-text (insecure) remote access protocol

ssh – Secure SHell – encrypted remote access client

check out the SSH reference!

File transfers  commands

Always useful to know how to copy files between servers or just download some package from the web:

ftp – clear-text (insecure!) File Transfer Protocol client

sftp – secure (encrypted) version of FTP

scp – secure (encrypted) version of cp command

wget – download files from remote servers, HTTP/HTTPS and FTP

Tail Command:- It gives last 10 lines.

tail file_name

tail -1 file_name

head command:- It gives first 10 lines.

head file_name

Print the content of the file

tail -n +2 ant5.txt | head -n -1

Check running process time using

ps -p 1388 -o etime

Print Line between M and N

head -n 20 state.txt | tail -10

Cut particular field for a file 

name,sex,house_nr,height,shoe_size

arthur,m,42,181,11.5

berta,f,101,163,8.5

chris,m,1333,175,10

don,m,77,185,12.5

elisa,f,204,166,7

cut -d',' -f2-4 abc1.txt

How to find duplicate records in file without writing sql query?

123

123

234

234

123

345

I would like to find how many times '123' was duplicated, how many times '234' was duplicated, etc. So ideally, the output would be like:

123  3

234  2

345  1

sort <file> | uniq -c

You can use the more verbose --count flag too with the GNU version, e.g., on Linux:

sort <file> | uniq --count

How to find the count of an word in the file?

grep –ow "hello" test.txt | wc –l

How to find the last 50 lines and first 50 lines in the file?

tail -50 test_text.txt

head -50 test_text.txt  > test1.txt

How to find the lines from 10 to100 in the file

tail -n +10 input.txt | head -n 91 > output.txt

How to change owner and group of file?

chgrp oracle:db input.txt

How to change permission of the file?

chmod wg+rwx input.txt

How to create , append and view the file?

cat  >  input.txt
cat >> input.txt
cat input.txt

How find the duplicate records in the file?

sort FILE | uniq -cd
sort FILE | uniq --count --repeated

How find the duplicate records counts including unique records

sort FILE | uniq -c

sort File | uniq --count

AWK commands

Awk options program file

Awk –F “,” ‘{print $0}’ test.txt

Awk –F “,” ‘{if ($1==123) print $0}’ test.txt