Linux command line directory commands

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danielmapar/LinuxCommandLine

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README.md

• date : current date
• cal : current months calendar
• cal 1999 : calendar for 1999
• cal -3 : calendar (last month, current and next month)
• cal -y : all year calendar
• clear : clear console text
• exit : exits de terminal

• bin: binary (commands and utilities that all users can run)
• sbin: this directory contains programs that performs vital system tasks (network management, disk partitioning). Only the superuser has access to these programs.
• home: each user is given a directory under the home directory. A user can store anything in his home directory
• opt: optional (additional software)
• tmp: temporary files, files created by various programs (Generally cleared on reboot)
• var: variable data, data that frequently changes over time.
  • Log files
  • Data bases
  • User mail
  • Spools -> temporary storage location
    • /var/spool is traditionally used for machine-local data being spooled to or from UNIX subsystems. For example, print jobs are spooled here for delivery to the lineprinter daemon, out-bound mail is spooled for delivery to remote systems, and UUCP files are spooled for transmission to UUCP neighbors. In-bound mail and news are spooled here for delivery to users, and at and cron jobs are spooled for delayed execution by the cron daemon.

    

    • pwd : print working directory
    • ls : list directory
    • cd : change directory
    • cd / : take you to the root directory
    • cd ~ : take you to the user home directory
    • cd ./another_folder : navigate from current directory to another_folder
    • cd .. : navigate from current directory to parent directory
    • cd — : go back to the previous working directory
      • cd / : going to the root directory
      • cd ~/ : going to the home directory
      • cd — : going back to the root directory

      

      • Every file in the system has an inode (Index node)
        • Contains all file information except the file content and name
        • A database of a file
        • They contain:
          • Inode number
          • File size
          • Owner information
          • Permission
          • File type
          • Number of links
            • Soft Link
            • Hard Link
            • A soft link is the same as a shortcut in Windows
            • Aka Symbolic link
            • It is a pointer to the original file
            • It is a file pointing to another file
              • Different inode number

              

              • Different name of the same file
              • Same file size
              • Same inode number
              • You cannot differentiate between a real file and a hard link
              • They are kind of a copy of the file
              • If I change a hard link file content, it will reflect on the other files (the original and other hard links)
              • In case I delete the original file, the hard link file will still work
              • Be careful: You should not create hard links for directories. Normally they are not even allowed because they break the file system structure.

              

              • ls : List files by alphabetic order
              • ls -i : This will list the index node number of each file
              • ls -a : This will show all the files (-a == all files) in your current directory, including hidden files
              • ls -l : Long listing of all files in the directory and some important information.
              • ls -t : Sort files by modification date
              • ls -r : List the files in reverse fashion (in this case reverse based on alphabetic order)
              • ls -rt OR ls -r -t : List the file in reverse fashion (in this case reverse based on modification date)
              • ls -li : Long listing + show inode ids
              • ls -lia : Long listing + show inode ids + hidden files
              • ls -R : Show current directory content plus any children/sub directory content as well
              • ls -Ra : Show current directory content plus any children/sub directory content as well + including hidden files

              Touch Command (Create a file)

              • Touch is used to create empty files
                • touch file_name : Create a file called file_name
                • touch file_name1 file_name2 file_name3 : Creates 3 files
                • touch ‘my file’ or touch «my file» or touch my\ \ file : create a file with a name containing spaces
                  • \ is a scape sequence
                  • touch newFile
                  • echo «test» > newFile
                  • touch newFile : this will update the file timestamp and keep the content

                  

                  MKDIR (Make directory) and RMDIR (Remove directory) Commands

                  mkdir directory_name mkdir directory_name1 directory_name2 directory_name3 

                  mkdir empty_dir rmdir empty_dir 

                  • In case you do rmdir in one directory that has files and another that is empty, it will only delete the empty one.

                  touch fileToDelete rm fileToDelete mkdir folder cd folder touch file cd .. 

                  • rm -R folder or rm -r folder
                  • In case of non-empty-directory you need to run rm with the recursive flag -R . Otherwise it will fail
                  • Also, the -R flag can be lowercase since it is not case sensitive for rm (although it is case sensitive for ls )
                  • rm -i : Prompt you before removing any existing file. the -i means interactive mode
                  • rm -f : Never prompt you before removing a file. And will not display a warning if the file you are trying to delete does not exist, meaning that it will ignore non existent files. -f means force
                  • rm -v : Verbose mode. It will print the name of each file before removing it.
                  • rm -R or rm -r : Recursively delete files. If the file is a directory, remove the entire directory and all its contents, including subdirectories.
                  • The cp command copies files or directories. It can be used in two different ways:
                    • Copy a file: cp file file2
                    • Make a copy of a directory: cp -R dir dir2 : dir2 does not need to exist
                      • This will make a copy of dir1 named dir2 (Assuming that dir2 didn’t exist)
                      • cp -i : Before overwriting an existing file, prompt the user for confirmation. cp will silently overwrite files by default.
                      • cp -v : Verbose mode (print the name of each file that was copied).
                      • cp -R : Recursively copy directories and their content. Just like the rm command, this option must be specified when copying a directory.
                      • cp -r : Same as cp -R
                      • The mv command can be used in two different ways.
                        • Renaming files
                          • mv file1 file2 : This will rename file1 to file2
                          • mv dir1 dir2 : If your file is a directory, this will rename the directory
                          • You do not need to use the -R option with mv
                          • mv file1 file2 dir1 : This will move file1 and file2 to dir1. However, dir1 must exist
                          • mv dir1 dir2 dir3 : This will move dir1 and dir2 to dir3. Again, dir3 must exist
                          • mv -i : Before overwriting an existing file, prompt the user for confirmation. If the option is not specified mv will silently overwrite the file
                          • mv -v : Verbose mode (print the name of each file that was moved or renamed)
                          • Filenames are case sensitive in just like the commands are.
                          • Linux has no concept of file extension like Windows. You can have files without any extension.
                            • It checks the file content to identify what kind is it.
                            • history : Show all the commands executed in the cmd
                            • history 10 : Show last 10 commands
                            • history -c : Clear history
                              • Your history is stored at ~/.bash_history
                              • Control+a : Start of the line
                              • Control+e : End of the line
                              • Control+d : Remove character from left to right
                              • Control+l : Clear

                              View text files (less, cat, tac, head, tail) Commands

                              • less file1 : View the content of the file file1
                                • Press q to quit
                                • cat lets you see two files output concatenated
                                • wc file : Presents the data like -> Number of lines, number of words, number of bytes
                                • wc -l : Show just number of lines
                                • wc -w : Show just number of words
                                • wc -c : Show just number of bytes
                                • wc -L : Length of longest line in characters
                                • bash : Born again shell
                                • Executable programs
                                  • They are inside /bin and usr/bin .
                                  • Example: cp command
                                  • cd command
                                  • In computing, a shell builtin is a command or a function, called from a shell, that is executed directly in the shell itself, instead of an external executable program which the shell would load and execute. Shell builtins work significantly faster than external programs, because there is no program loading overhead. However, their code is inherently present in the shell, and thus modifying or updating them requires modifications to the shell. Therefore, shell builtins are usually used for simple, almost trivial, functions, such as text output.
                                  • Custom programs written in shell script
                                  • ls command
                                  • Create your own commands
                                  • The alias command makes it possible to launch any command or group of commands (inclusive of any options, arguments and redirection) by entering a pre-set string (i.e., sequence of characters).
                                  • It displays if command is an alias, shell function, shell builtin, disk file, or shell reserved word.
                                  • type ls : ls is hashed (/bin/ls)
                                  • type cd : cd is a shell builtin
                                  • type cp : cp is /bin/cp
                                    • file /bin/cp : tells you that cp is an executable
                                    • which cp : display executable location /bin/cp
                                    • Also for executables, you can do whatis cp to get a short description about the program

                                    Execute multiple commands

                                    • date; cal : Separate commands using a semicolon
                                    • mkdir test && cd test1 && cd test : Different from ; the operand && stops the execution if one of the commands fail (short circuit evaluation)
                                    • * : all occurrences
                                      • cp *.txt dir
                                      • cp * dir
                                      • cp [abc]*.txt dir : Copy all the file that begins with the letters abc to dir
                                      • cp [!abc]*.txt dir : Copy all the file that does not begins with the letters abc to dir
                                        • Exclamation mark negates the command
                                        • alias myname=»cd Desktop;mkdir dir» : Create an alias called myname that goes to the Desktop folder and creates a directory called dir
                                        • unalias myname : Delete an alias
                                        • To retain an alias, save it inside ~/.bashrc
                                        • alias : List of all alias in the system
                                        • > operator
                                          • e.g. grep «text» . > output.txt
                                          • Writing to a file (overwrite)
                                          • e.g head -n1 < /etc/passwd
                                            • Using operator as input to an app
                                            • e.g. grep «text» . >> output.txt
                                            • Append to a file
                                            • ps aux
                                              • a = —all Display information about other users’ processes as well as your own.
                                              • u = Display the processes belonging to the specified usernames.
                                              • x = When displaying processes matched by other options, include processes which do not have a controlling terminal.

                                              Users, Groups and Permissions

                                              Environment Variables and RC Files

                                              • echo $USER
                                              • echo $HOME
                                              • echo $0
                                                • my shell name
                                                • Path to find binaries
                                                • PATH=$PATH:newfolder
                                                • .bashrc = Bash Run Commands.
                                                • the keyword export guarantees that if our current process spins child processes, it will also export this env var to the children processes.

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