Linux Commands and Concepts

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1. pwd - Print Working Directory

Description: Shows the full path of the current directory.
Examples:

• pwd
  Example Output: /home/user/documents
• pwd -P
  Displays the physical directory, avoiding symlinks.
  Example Output: /home/user/documents
• pwd -L
  Displays the logical path with symlinks (default).
  Example Output: /home/user/../documents

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2. ls - List Files

Description: Lists files in a directory.
Examples:

• ls
  Example Output: file1.txt file2.txt folder
• ls -lh
  Lists files with detailed information (size, permissions, etc.).
  Example Output: -rw-r--r-- 1 user user 1.2K Sep 1 12:00 file1.txt
• ls -a
  Shows hidden files.
  Example Output: file1.txt .hiddenfile folder

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3. cd - Change Directory

Description: Changes the current directory.
Examples:

• cd /path/to/directory
  Example: Changes to /path/to/directory
• cd ..
  Moves up one directory.
  Example: Moves to /path/to from /path/to/directory
• cd ~
  Changes to the user's home directory.
  Example: Changes to /home/user
• cd -
  Switches back to the previous directory.
  Example: Returns to /home/user from /var/log

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4. mkdir - Create Directory

Description: Creates a new directory.
Examples:

• mkdir myfolder
  Example: Creates /home/user/myfolder
• mkdir -p /path/to/folder
  Creates nested directories.
  Example: Creates /path/to/folder, including intermediate directories.

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5. cp - Copy Files

Description: Copies files or directories.
Examples:

• cp file1.txt /backup/
  Example: Copies /home/user/file1.txt to /home/user/backup/
• cp -p file1.txt /backup/
  Preserves file permissions.
  Example: Copies /home/user/file1.txt while preserving permissions
• cp -r folder/ /backup/
  Recursively copies a directory and its contents.
  Example: Copies /home/user/folder/ to /home/user/backup/folder/

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6. mv - Move or Rename Files

Description: Moves or renames files or directories.
Examples:

• mv file1.txt file2.txt
  Example: Renames /home/user/file1.txt to /home/user/file2.txt
• mv file1.txt /backup/
  Example: Moves /home/user/file1.txt to /home/user/backup/
• mv -v file1.txt /backup/
  Verbosely shows the move operation.
  Example Output: ‘file1.txt’ -> ‘/backup/file1.txt’
• mv -n file1.txt /backup/
  Prevents overwriting existing files.
  Example: If /backup/file1.txt exists, it will not be overwritten.
• mv -vn file1.txt /backup/
  Verbosely and without overwriting.
  Example Output: ‘file1.txt’ -> ‘/backup/file1.txt’ (skipped: file exists)

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7. rm - Remove Files

Description: Deletes files or directories.
Examples:

• rm file1.txt
  Example: Deletes /home/user/file1.txt
• rm -r folder/
  Recursively deletes a directory and its contents.
  Example: Deletes /home/user/folder/ and all its contents
• rm -f file1.txt
  Force removes a file without confirmation.
  Example: Deletes /home/user/file1.txt without prompting
• rm -rf folder/
  Forcefully and recursively deletes a folder.
  Example: Deletes /home/user/folder/ and all its contents without confirmation

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8. Background and Foreground Jobs

Description: Managing process execution.
Examples:

• command &
  Runs command in the background.
  Example: sleep 60 & runs sleep in the background.
• jobs
  Lists all background jobs.
  Example Output: [1] 1234
• fg %1
  Brings job number 1 to the foreground.
  Example: Moves sleep from the background to the foreground.
• bg %1
  Resumes job number 1 in the background.
  Example: Continues sleep in the background.

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9. Using screen for Management

Description: Terminal multiplexing tool.
Examples:

• screen
  Starts a new screen session.
  Example: Creates a new session to manage multiple terminal windows.
• screen -ls
  Lists all active screen sessions.
  Example Output: There is a screen on: 1234.pts-0.hostname (Detached)
• screen -r 1234
  Reattaches to the screen session with ID 1234.
  Example: Reconnects to a detached session.
• Ctrl+A followed by d
  Detaches from the current screen session.
  Example: Detaches from a session, leaving it running in the background.

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10. Linux Size Conversion

Description: Convert between different file sizes.
Examples:

• ls -lh
  Displays file sizes in human-readable format (e.g., KB, MB).
  Example Output: 1.2K
• du -sh /path/to/dir
  Shows the size of a directory in a human-readable format.
  Example Output: 1.5G
• stat -c %s file.txt
  Displays the file size in bytes.
  Example Output: 123456

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11. How File Permissions Work in Linux

Description: Understanding file permissions.
Examples:

• ls -l
  Displays file permissions in a detailed list.
  Example Output: -rwxr-xr-- 1 user group 12345 Sep 1 12:00 file.txt
• chmod 755 file.txt
  Sets file permissions to rwxr-xr-x.
  Example: Owner can read/write/execute, others can read/execute.
• chown user:group file.txt
  Changes the owner and group of a file.
  Example: Changes ownership to user and group.

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12. File Permissions and Ownership

Description: Detailed permissions and ownership management.
Examples:

• chmod
  Modify file permissions.
  Example: chmod u+x file.txt adds execute permission for the user.
• chown
  Change file ownership.
  Example: chown user file.txt changes the owner to user.
• chgrp
  Change the group ownership of a file.
  Example: chgrp group file.txt changes the group to group.

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13. Useful Linux Commands for Data Analysis

Description: Commands for processing and analyzing data.
Examples:

• awk '{print $1}' file.txt
  Extracts and prints the first column from a file.
  Example Output: Displays the first column from file.txt.
• sort file.txt
  Sorts the contents of a file.
  Example Output: Sorted lines of file.txt.
• uniq file.txt
  Removes duplicate lines from a file.
  Example Output: Unique lines from file.txt.
• cut -d' ' -f1 file.txt
  Extracts the first field from each line using space as the delimiter.
  Example Output: First field of file.txt.

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14. Combining Commands with Pipes and Redirection

Description: Using pipes and redirection to combine commands.
Examples:

• command1 | command2
  Sends the output of command1 as input to command2.
  Example: ls | grep 'file' lists files and filters those containing 'file'.
• command > file.txt
  Redirects the output of command to file.txt, overwriting it.
  Example: echo "Hello" > file.txt writes "Hello" to file.txt.
• command >> file.txt
  Appends the output of command to file.txt.
  Example: echo "World" >> file.txt appends "World" to file.txt.

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15. Automating Tasks with while and for Loops

Description: Automating repetitive tasks with loops.
Examples:

• while loop

  while [ condition ]; do
      command
  done
  
  while [ $count -lt 5 ]; do
      echo $count
      ((count++))
  done
  
  

• for loop

  for item in list; do
    command
  done
  
  for file in *.txt; do
      cat "$file"
  done
  
  

16. Understanding Data Size Conversion

Title: Data Size Conversion: Bytes, Kilobytes, Megabytes, Gigabytes

Content:

• Basic Units of Data:

  • Bit (b): The smallest unit, 0 or 1.
  • Byte (B): 1 Byte = 8 bits.

• Common Data Size Conversions:

  • 1 Kilobyte (KB): 1 KB = 1,024 Bytes.
  • 1 Megabyte (MB): 1 MB = 1,024 KB.
  • 1 Gigabyte (GB): 1 GB = 1,024 MB.
  • 1 Terabyte (TB): 1 TB = 1,024 GB.

• Example:

  • A 10 MB file is equal to 10 * 1,048,576 = 10,485,760 Bytes.

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