Linux Shell Tips and Tricks: 73 Useful Commands

1. Check if a remote port is open for bash: echo >/dev/tcp/8.8.8.8/53 && echo "open" 2. Send a process to the background: Ctrl + z 3. Bring a process to the foreground: fg 4. Generate a random hexadecimal string of n characters: openssl rand -hex n 5. Execute commands from a file in the current shell: source /home/user/file.name 6. Extract the first 5 characters of a variable: ${variable:0:5} 7. SSH debug mode: ssh -vvv user@ip_address 8. SSH with a PEM key: ssh user@ip_address -i key.pem 9. Use wget to download an entire website directory structure to a local folder:

wget -r --no-parent --reject "index.html*" http://hostname/ -P /home/user/dirs

10. Create multiple directories at once: mkdir -p /home/user/{test,test1,test2} 11. List the process tree including child processes: ps axwef 12. Create a WAR file: jar -cvf name.war file 13. Test disk write speed:

dd if=/dev/zero of=/tmp/output.img bs=8k count=256k; rm -rf /tmp/output.img

14. Test disk read speed: hdparm -Tt /dev/sda 15. Get the MD5 hash of a text string: echo -n "text" | md5sum 16. Check XML format: xmllint --noout file.xml 17. Extract a tar.gz archive into a new directory: tar zxvf package.tar.gz -C new_dir 18. Retrieve HTTP headers with curl: curl -I http://www.example.com 19. Change file or directory timestamp (YYMMDDhhmm): touch -t 0712250000 file 20. Use wget to perform an FTP download: wget -m ftp://username:password@hostname 21. Generate a random 16‑character password:

LANG=c < /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c${1:-16};echo;

22. Quickly backup a file: cp some_file_name{,.bkp} 23. Access a Windows share directory: smbclient -U "DOMAIN\user" //dc.domain.com/share/test/dir 24. Execute a command from history (line 100): !100 25. Unzip a package to a directory: unzip package_name.zip -d dir_name 26. Input multiple lines of text (Ctrl + D to exit): cat > test.txt 27. Create an empty file or truncate an existing one: > test.txt 28. Sync time with Ubuntu NTP server: ntpdate ntp.ubuntu.com 29. Show all listening TCP4 ports:

netstat -lnt4 | awk '{print $4}' | cut -f2 -d: | grep -o '[0-9]*'

30. Convert a qcow2 image to raw:

qemu-img convert -f qcow2 -O raw precise-server-cloudimg-amd64-disk1.img precise-server-cloudimg-amd64-disk1.raw

31. Repeatedly run a command and display its output (default every 2 seconds): watch ps -ef 32. List all users: getent passwd 33. Remount root filesystem as read/write: mount -o remount,rw / 34. Bind‑mount a directory (no symlink): mount --bind /source /destination 35. Dynamically update a DNS server:

nsupdate <<EOF
update add $HOST 86400 A $IP
send
EOF

36. Recursively grep all directories: grep -r "some_text" /path/to/dir 37. List the top 10 largest files:

lsof / | awk '{ if($7 > 1048576) print $7/1048576 "MB " $9 }' | sort -n -u | tail

38. Show remaining memory (MB): free -m | grep cache | awk '/[0-9]/{ print $4" MB" }' 39. Open Vim and jump to the end of a file: vim + some_file_name 40. Clone a specific branch (master) with Git: git clone [email protected]:name/app.git -b master 41. Switch to another branch (develop) with Git: git checkout develop 42. Delete a branch (myfeature) with Git: git branch -d myfeature 43. Delete a remote branch with Git: git push origin :branchName 44. Push a new branch to a remote server: git push -u origin mynewfeature 45. Print the last cat command from history: !cat:p 46. Run the last cat command from history: !cat 47. Find all empty sub‑directories under /home/user: find /home/user -maxdepth 1 -type d -empty 48. Show lines 50‑60 of test.txt: < test.txt sed -n '50,60p' 49. Re‑execute the last command with sudo if needed: sudo !! 50. Create a temporary RAM filesystem (ramdisk) of 512 MiB: mount -t tmpfs tmpfs /tmpram -o size=512m 51. Grep whole words: grep -w "name" test.txt 52. Append text to a file with elevated privileges: echo "some text" | sudo tee -a /path/file 53. List all kill signal names: kill -l 54. Prevent the last session from being recorded in bash history: kill -9 $$ 55. Scan a network for open ports: nmap -p 8081 172.20.0.0/16 56. Set Git email address: git config --global user.email "[email protected]" 57. Sync with master when you have unpublished commits: git pull --rebase origin master 58. Move all files containing "txt" in their name to /home/user: find -iname "*txt*" -exec mv -v {} /home/user \; 59. Display files side‑by‑side by columns: paste test.txt test1.txt 60. Show a progress bar for data in a shell pipeline: pv data.log 61. Send data to a Graphite server using netcat:

echo "hosts.sampleHost 10 `date +%s`" | nc 192.168.200.2 3000

62. Convert tabs to spaces: expand test.txt > test1.txt 63. Skip bash history for a command: < space >cmd 64. Return to the previous working directory: cd - 65. Split a large tar.gz archive into 100 MiB parts and later re‑assemble:

split –b 100m /path/to/large/archive /path/to/output/files
cat files* > archive

66. Get HTTP status code with curl: curl -sL -w "%{http_code}\n" www.example.com -o /dev/null 67. Harden MySQL installation and set root password: /usr/bin/mysql_secure_installation 68. When Ctrl + C does not work, use: Ctrl + \ 69. Get the owner of a file: stat -c %U file.txt 70. List block devices with filesystem information: lsblk -f 71. Find files whose names end with a space: find . -type f -exec egrep -l " +$" {} \; 72. Find files whose names contain a tab character: find . -type f -exec egrep -l '\t' {} \; 73. Print a line of 100 equal signs:

printf '%100s
' | tr ' ' =