As you spend more and more time working on Linux environment, you tend to learn some cool tricks that make your life easy and save you lot of time. I have been working on Linux command line for many years now and I have learned a lot of Linux command line tricks. Here in this article, I have posted most of the useful command that each beginner should know.

• Check if remote port is open with bash:  echo >/dev/tcp/8.8.8.8/53 && echo "open"
• Suspend process:  Ctrl + z
• Move process to foreground:  fg
• Generate random hex number where n is number of characters:  openssl rand -hex n
• Execute commands from a file in the current shell:  source /home/user/file.name
• Substring for first 5 characters: ${variable:0:5}
• SSH debug mode:  ssh -vvv user@ip_address
• SSH with pem key:  ssh user@ip_address -i key.pem
• Get complete directory listing to local directory with wget:  wget -r --no-parent --reject "index.html*" http://hostname/ -P /home/user/dirs
• Create multiple directories:  mkdir -p /home/user/{test,test1,test2}
• List processes tree with child processes:  ps axwef
• Create war file:  jar -cvf name.war file
• Test disk write speed:  dd if=/dev/zero of=/tmp/output.img bs=8k count=256k conv=fdatasync; rm -rf /tmp/output.img
• Test disk read speed:  hdparm -Tt /dev/sda
• Get md5 hash from text:  echo -n "text" | md5sum
• Check xml syntax:  xmllint --noout file.xml
• Extract tar.gz in new directory:  tar zxvf package.tar.gz -C new_dir
• Get HTTP headers with curl:  curl -I http://www.funwithtricks.com
• Modify time stamp of some file or directory (YYMMDDhhmm):  touch -t 0712250000 file
• Download from ftp using wget:  wget -m ftp://username:password@hostname
• Generate random password (16 char long in this case):  LANG=c < /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c${1:-16};echo;
• Quickly create a backup of a file:  cp some_file_name{,.bkp}
• Access Windows share:  smbclient -U "DOMAIN\user" //dc.domain.com/share/test/dir
• Run command from history (here at line 100):  !100
• Unzip to directory:unzip package_name.  zip -d dir_name
• Multiline text (CTRL + d to exit):  cat > test.txt
• Create empty file or empty existing one:  > test.txt
• Update date from Ubuntu NTP server:  ntpdate ntp.ubuntu.com
• netstat show all tcp4 listening ports:  netstat -lnt4 | awk '{print $4}' | cut -f2 -d: | grep -o '[0-9]*'
• Convert image from qcow2 to raw:  qemu-img convert -f qcow2 -O raw precise-server-cloudimg-amd64-disk1.img \ precise-server-cloudimg-amd64-disk1.raw
• Run command repeatedly, displaying it's output (default every two seconds):  watch ps -ef
• List all users:  getent passwd
• Mount root in read/write mode:  mount -o remount,rw /

• Mount a directory (for cases when symlinking will not work):  mount --bind /source /destination
• Send dynamic update to DNS server:  nsupdate < <EOF update add $HOST 86400 A $IP send EOF
• Recursively grep all directories:  grep -r "some_text" /path/to/dir
• List ten largest open files:  lsof / | awk '{ if($7 > 1048576) print $7/1048576 "MB "$9 }' | sort -n -u | tail
• Show free RAM in MB:  free -m | grep cache | awk '/[0-9]/{ print $4" MB" }'
• Open Vim and jump to end of file:  vim + some_file_name
• Git clone specific branch (master):  git clone git@github.com:name/app.git -b master
• Git switch to another branch (develop):  git checkout develop
• Git delete branch (myfeature):  git branch -d myfeature
• Git delete remote branch:git push origin :  branchName
• Git push new branch to remote:  git push -u origin mynewfeature
• Print out the last cat command from history:  !cat:p
• Run your last cat command from history:  !cat
• Find all empty subdirectories in /home/user:  find /home/user -maxdepth 1 -type d -empty
• Get all from line 50 to 60 in test.txt:  < test.txt sed -n '50,60p'
• Run last command (if it was: mkdir /root/test, below will run:  sudo mkdir /root/test):sudo !!
• Create temporary RAM filesystem - ramdisk (first create /tmpram directory):  mount -t tmpfs tmpfs /tmpram -o size=512m
• Grep whole words:  grep -w "name" test.txt
• Append text to a file that requires raised privileges:  echo "some text" | sudo tee -a /path/file
• List all supported kill signals:  kill -l
• Generate random password (16 characters long in this case):  openssl rand -base64 16
• Do not log last session in bash history:  kill -9 $
• Scan network to find open port:  nmap -p 8081 172.20.0.0/16
• Set git email:  git config --global user.email "me@example.com"
• To sync with master if you have unpublished commits:  git pull --rebase origin master
• Move all files with "txt" in name to /home/user:  find -iname "*txt*" -exec mv -v {} /home/user \;
• Put the file lines side by side:  paste test.txt test1.txt
• Progress bar in shell:  pv data.log
• Send the data to server with netcat:  echo "hosts.sampleHost 10 `date +%s`" | nc 192.168.200.2 3000
• Convert tabs to spaces:  expand test.txt > test1.txt
• Skip bash history:  < <space>>cmd
• Go to the previous working directory:  cd -
• Split large tar.gz archive (100MB each) and put it back:  split –b 100m /path/to/large/archive /path/to/output/files cat files* > archive
• Get HTTP status code with curl:  curl -sL -w "%{http_code}\\n" www.example.com -o /dev/null
• When Ctrl + c not works:  Ctrl + \
• Get file owner:  stat -c %U file.txt
• List block devices:  lsblk -f
• Find files with trailing spaces:  find . -type f -exec egrep -l " +quot; "{}" \;
• Find files with tabs indentation:  find . -type f -exec egrep -l #39;\t' "{}" \;