CHEAT SHEET ABOUT LINUX COMMANDS

Checking the Type of a Command

• Use type to see if a command is built-in or external:

   

  type cd type cal

• Add -a to show all possible locations for a command:

   

  type -a echo

Finding Where a Command Is Located

• which looks through your PATH to find where a command is:

   

  which ls which cal

• whereis gives you the path to the binary, source, and man pages:

   

  whereis ls

• locate searches a pre-built database of files on your system:

   

  locate gshadow

Creating Aliases and Functions

• Set a quick alias:

   

  alias today="date" today

• Define a simple function:

   

  my_func() { command1 command2 }

  Example:

   

  show_home() { ls -l /home echo "Done" } show_home

Combining Commands

• ; runs multiple commands in sequence, regardless of success:

   

  cal 1 2030 ; cal 2 2030 ; cal 3 2030

• | (pipe) passes the output of one command to another:

   

  cal 1 2030 | cal 2 2030

• && runs the second command only if the first one works:

   

  ls /etc/ppp/ && echo "Success"

• || runs the second command only if the first one fails:

   

  ls /etc/ppp/ || echo "ls failed"

📚 Getting Help and Documentation

• man opens the manual for a command:

   

  man ls

• whatis gives a short description and man section:

   

  whatis ls

• info opens a more detailed help system:

   

  info ls

• --help gives a brief overview of how to use a command:

   

  cat --help

• README files (docs):

   

  ls /usr/share/doc

Navigation and Wildcards

• pwd: Shows your current directory.

• Wildcards:

  • * = any number of characters

  • ? = exactly one character

  • [ab] = any character listed between brackets

  Examples:

   

  echo /etc/s* # Starts with "s" echo /etc/t??????? # Starts with "t" + 7 characters echo /etc/[gu]* # Starts with "g" or "u"

Working with Files

• Copy with verbose output:

   

  cp -v file1 file2

• Create an archive using tar:

   

  tar -cf archive.tar file.png

Viewing File Content

• Use less to scroll through large files (H for help).

• head shows the top lines of a file:

   

  head /etc/sysctl.conf

• tail shows the bottom lines:

   

  tail -5 /etc/sysctl.conf

Text Processing Tools

• sort: Orders lines alphabetically:

   

  sort /etc/sysctl.conf

• wc: Counts lines, words, and characters:

   

  wc /etc/sysctl.conf

• cut: Extracts fields from a file using a delimiter:

   

  cut -d: -f1,5-7 mypasswd

• grep: Filters lines based on a matching pattern:

   

  grep bash /etc/passwd grep 'r..f' red.txt # Matches words with r, any 2 chars, then f