Mastering the Asterisk (*) in Bash: A Comprehensive Guide

The asterisk (*) is one of the most powerful and frequently used wildcard characters in Bash. Whether you're listing files, moving directories, or searching for patterns, mastering the use of * can significantly boost your efficiency in the terminal. This article explores various ways to use * in Bash, with practical examples to help you get the most out of this wildcard.

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1. Wildcard for File and Directory Matching

• The * wildcard matches zero or more characters in filenames.

• Example:

  ls *.txt  # Lists all files ending with .txt
  ls file*  # Lists all files starting with "file"
  

2. Using * in Commands

• The * wildcard works with commands like cp, mv, rm, etc.

• Example:

  cp *.jpg backup/  # Copies all .jpg files to the backup directory
  rm *              # Deletes all files in the current directory
  

3. Wildcard in Recursive Search

• Used with find or grep to search files recursively.

• Example:

  find . -name "*.sh"  # Finds all .sh files in current directory and subdirectories
  grep "error" *.log    # Searches for "error" in all .log files
  

4. Repeating the Last Argument (!*)

• Expands to the last argument of the previous command.

• Example:

  echo Hello World
  echo !*  # Expands to "World"
  

5. Arithmetic Expansion (* as a Multiplication Operator)

• Used in arithmetic operations within $(( )).

• Example:

  echo $((5 * 3))  # Prints 15
  

6. Globbing with Extended Patterns

• Works with shopt -s extglob to enable advanced patterns.

• Example:

  shopt -s extglob
  ls !(file1.txt)  # Lists all files except file1.txt
  

7. Using * in Variable Expansion

• Expands filenames matching a pattern into a variable.

• Example:

  FILES=(*.txt)
  echo "${FILES[@]}"  # Prints all .txt files
  

8. Escaping * to Treat as a Literal Character

• Use \* or quotes to prevent wildcard expansion.

• Example:

  echo "*"  # Prints *
  

9. Using * in Pathname Expansion

• Works in paths to match files and directories.

• Example:

  cp ~/Documents/*.pdf ~/Backup/  # Copies all PDFs from Documents to Backup
  

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Advanced Uses of * in Bash

10. Using * with apt Commands

apt list --installed alsa*

• Lists all installed packages whose names start with alsa.

apt install alsa*

• Installs all packages that start with alsa.

11. File Removal Patterns

rm *.exe

• Deletes all .exe files in the current directory.

rm he*.deb

• Deletes all .deb files that start with "he".

12. Excluding Files (rm !(*.c))

rm !(*.c)

• Deletes all files except those ending with .c.

• Requires enabling extended globbing:

  shopt -s extglob
  

13. Moving and Copying Files

mv *.txt backup/
cp *.jpg images/

• Moves all .txt files into the backup/ directory.

• Copies all .jpg files into the images/ directory.

14. Removing Empty Directories (rmdir */)

rmdir */

• Removes all empty directories in the current location.

15. Counting Matching Files (ls *.log | wc -l)

ls *.log | wc -l

• Counts the number of .log files in the current directory.

16. Using * in tar Commands

• Archive all .log files:

  tar -cvf logs.tar *.log
  

17. Wildcard in rsync

• Sync all .jpg files to a backup folder:

  rsync -av *.jpg backup/
  

18. Using * in echo for Expansion

echo *.txt

• Prints a list of all .txt files in the current directory.

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Final Thoughts

Understanding how the asterisk (*) works in Bash can make your command-line experience much more efficient. From simple file management to advanced pattern matching, * is an essential tool for any Linux user. Experiment with these commands and see how they can streamline your workflow!