Linux

• General Command Syntax :

  • Command Option(s) Arguments
  • 1. ls -lh /user/bin
    2. sort user.txt
    3. grep -i "needle" haystack

• File and Folders

  1. file -> syntax : file filename

     • Determines file type, examines file contents rather than its name or extension to identify what kind of file it is.
     • eg. file Linux_Notes
     • output -> Linux_Notes : ASCII text

  2. stat -> syntax : stat filename

     • display detailed information about file or file system like includes information like the file's size, permissions, owner, modification time, etc.
     • eg. stat Linux_Notes
     • output ->

• ls command working :

  1. ls -R departments : The ls -R departments lists all files and directories within a specified directory and does so recursively, i.e it will include the contents of all subdirectories as well.
     • output ->
  2. ls -l : ls -l lists the contents of a directory in long format. This long listing format provides detailed information about each file or directory.
     • output->

       Field	Example Value	Description
       File Type & Permissions	-rwxrwxrwx	Indicates the type of file and the permissions for user, group, and others.
       Number of Links	1	Number of hard links to the file or directory.
       Owner (User)	yash	The user who owns the file.
       Group	yash	The group that owns the file.
       File Size	1474	Size of the file in bytes.
       Modification Date & Time	June 19 2018	Date and time when the file was last modified.
       File Name	poems.txt	The name of the file or directory.

• Create and Remove Folders

  1. Create Folder : mkdir foldername Creates folder in current working directory.

     • eg. mkdir yash_docs
     • if I want to create folder inside another folder of current working directory
       • mdkir yash_docs/college/Marksheets
     • if we want to create folder with sub folder inside it we need to pass option in command
       • mkdir -p yash_docs/college/DBMS_LAB/Practicals

  2. Remove Folder: rmdir foldername removes empty folder ( removes folder only when empty)

     • eg. rmdir new_folder

• Copy File and Folder

  1. Copying file: cp originalfile copyfile creates copy of originalfile with name copyfile name

     • eg 1. cp file1.txt file1_copy.txt
     • eg 2. cp file1.txt departments/images/file1_copy.txt

  2. Copying folder: cp -r originalfolder copyfolder creates copy of originalfolder with name copyfolder*

     • eg 1. cp -r folder1 copyfolder1
     • eg 2. cp -r folder1 departments/images/copyfolder2

• Moving file and folder

  1. mv file1.txt file2.txt : move file in same directory and save it with name file2.txt
  2. mv file1.txt departments/images/file2.txt : move file from current working directory to different directory with name file2.txt
  3. mv departments/images/file1.txt : move file from different directory to current working directory with name file2.txt.
  4. mv *.txt departments/images : moves all the textfiles to images folder.
  5. mv departments/images/* . : moves all the files and folders in images to current working directory.

  NOTE: Same can be used for moving folders. eg: mv folder1 folder2

• Remove file and folder

  1. rm file.txt : removes file.txt
  2. rm -r departments : removes folder from current working directory

• Find : Used to search for files and directories within a directory hierarchy.

  • Syntax : find < path > < options > < expression >

    • path : Specifies the directory or directories in which to start the search
    • options : Control the behavior of the find command, such as limiting the depth of the search or controlling the output.
    • expression : criteria for matching files or directories. These can include name patterns, file sizes, modification times, ownership, permissions, etc.

  • eg. find . -name "po*" : searches for folder or directories with name starting from po in current working directory and its subdirectories

  • eg. find ~/Documents/departments -name "*d*"

  • eg. find ~/Documents/departments -type f -name ".txt"

• File Permissions : File permissions determine who can read, write, or execute a file or directory

  • file permission string has 10 characters.

    • first character indicate file type

    • next nine characters represents the permissions divided into three sets of three characters

      • Owner (user) permissions
      • Group permissions
      • Others permissions

    • eg. ls -l sample.txt

    • output->

    • Changing file permission using chmod (change permissions on a file by modifying file mode bits)

      1. using octal notation
      2. using symbolic notation

    • OCTAL Notation

      

      • Syntax : chmod octalnotation filename

        

    • Symbolic Notation

      • Symbolic notation uses letters to represent permissions and categories

        1. Permissions
           1. Read : r
           2. Write : w
           3. Execute : x
        2. Categories:
           1. User : u (owner)
           2. Group : g
           3. Others : o
           4. All (user, group, and others) : a
        3. Modifying Permissions : Permissions are modified using operators
           1. Add permission : +
           2. Remove permission : -
           3. Set exact permissions : =

        Symbolic Command	Permissions Set (rwxrwxrwx)	Description
        chmod u+r	r-------- (read for user)	Adds read permission for the user (owner)
        chmod g+rw	r--rw---- (write for group)	Adds write permission for the group
        chmod o+rwx	r--rw-rwx (execute for others)	Adds execute permission for others
        chmod u+x,g+x	r-xrwxrwx (execute for user and group)	Adds execute permission for user and group
        chmod u-rx	---rwxrwx (remove read/write for user)	Removes read and write permissions from user
        chmod g-x	---rw-rwx (remove execute for group)	Removes execute permission from group
        chmod a+rwx	rwxrwxrwx (read, write ,execute for all)	Adds read permission for all users (user, group, others)
        chmod u=rwx,g=rx,o=r	rwxr-xr--(set permissions as given in command)	Sets user to full access, group to read/execute, others read-only
        chmod o-rwx	rwxr-x--- (remove all for others)	Removes all permissions from others