Linux Commands

1. Basic Navigation Commands

• pwd (Print Working Directory)

  • Purpose: Displays the full path of the current directory you are in.

  • Example: $PWD (returns something like /home/user/documents)

• ls (List)

  • Purpose: Lists the contents of a directory.

  • Common Options:

  • -l: Long listing format (shows permissions, owner, group, size, date, name).

  • -a: All files (includes hidden files, which start with a dot .)

  • -h: Human-readable sizes (e.g., $1 ext{K}, 234 ext{M}, 2 ext{G}$)

  • Example: ls -lah

• cd (Change Directory)

  • Purpose: Changes the current working directory.

  • Common Usage:

  • cd /path/to/directory: Navigates to an absolute path.

  • cd directory_name: Navigates to a subdirectory relative to the current directory.

  • cd ..: Moves up one directory level.

  • cd: Navigates to the user's home directory.

  • cd -: Navigates to the previous working directory.

  • Example: cd ..

2. File Manipulation Commands

• touch

  • Purpose: Creates an empty file or updates the timestamp of an existing file.

  • Example: touch newfile.txt

• cp (Copy)

  • Purpose: Copies files or directories.

  • Common Options:

  • -r or -R: Recursive (required for copying directories).

  • -i: Interactive (prompts before overwriting).

  • Example: cp file.txt /path/to/destination/

  • Example (directory): cp -r directory/ /path/to/destination/

• mv (Move)

  • Purpose: Moves or renames files or directories.

  • Usage: Source and destination arguments similar to cp.

  • Example: mv oldname.txt newname.txt (rename)

  • Example: mv file.txt /path/to/destination/ (move)

• rm (Remove)

  • Purpose: Deletes files or directories.

  • Common Options:

  • -r or -R: Recursive (required for deleting non-empty directories).

  • -f: Force (deletes without prompting).

  • -i: Interactive (prompts before every deletion).

  • Example: rm oldfile.txt

  • Example (directory): rm -r olddirectory/

3. Directory Manipulation Commands

• mkdir (Make Directory)

  • Purpose: Creates a new directory.

  • Common Options:

  • -p: Parents (creates parent directories as needed).

  • Example: mkdir new_folder

  • Example: mkdir -p project/src/main

• rmdir (Remove Directory)

  • Purpose: Deletes an empty directory.

  • Note: rm -r is typically used for non-empty directories.

  • Example: rmdir empty_folder

4. Viewing File Content

• cat (Concatenate)

  • Purpose: Displays the content of a file to standard output.

  • Example: cat document.txt

• less

  • Purpose: Allows viewing file content one screen at a time (scrollable).

  • Usage: Press q to quit, arrow keys to scroll.

  • Example: less large_log_file.txt

• head

  • Purpose: Displays the beginning lines of a file (default: $10$ lines).

  • Common Options:

  • -n COUNT: Displays the first COUNT lines.

  • Example: head -n 5 file.txt

• tail

  • Purpose: Displays the ending lines of a file (default: $10$ lines).

  • Common Options:

  • -n COUNT: Displays the last COUNT lines.

  • -f: Follows (monitors) the file for new content (useful for logs).

  • Example: tail -n 5 file.txt

  • Example: tail -f /var/log/syslog

5. User and Permissions

• chmod (Change Mode)

  • Purpose: Changes file permissions.

  • Permissions: Read ($r=4$), Write ($w=2$), Execute ($x=1$)

  • Categories: User ($u$), Group ($g$), Others ($o$), All ($a$)

  • Symbolic Mode: chmod u+x filename (add execute for user)

  • Octal/Numeric Mode: Sum of permissions for each category ($rwx = 7, rw- = 6, r-x = 5$ etc.)

  • Example: chmod 755 script.sh (user: rwx, group: r-x, others: r-x)

  • Example: chmod go-w file.txt (remove write for group and others)

• chown (Change Owner)

  • Purpose: Changes the owner of a file or directory.

  • Example: chown user filename

  • Example (with group): chown user:group filename

• sudo (Substitute User Do)

  • Purpose: Allows a permitted user to execute a command as the superuser or another user.

  • Example: sudo apt update (requires password for elevated privileges)

• whoami

  • Purpose: Displays the current user's username.

  • Example: whoami

• man (Manual)

  • Purpose: Displays the manual page for a command.

  • Usage: Press q to quit.

  • Example: man ls