In this section, we will explore the powerful tools of wildcards and regular expressions in Linux. These tools allow you to perform complex searches and manipulations on text and files, making your command-line experience more efficient and effective.

Wildcards are special characters used in shell commands to represent one or more characters. They are particularly useful for matching file names and directories.

1. Asterisk (*)

   • Matches zero or more characters.
   • Example: *.txt matches all files with a .txt extension.

2. Question Mark (?)

   • Matches exactly one character.
   • Example: file?.txt matches file1.txt, file2.txt, but not file10.txt.

3. Square Brackets ([])

   • Matches any one of the enclosed characters.
   • Example: file[123].txt matches file1.txt, file2.txt, and file3.txt.

4. Square Brackets with Hyphen ([a-z])

   • Matches any one character within the specified range.
   • Example: file[a-c].txt matches filea.txt, fileb.txt, and filec.txt.

Regular expressions (regex) are sequences of characters that define search patterns. They are used in many Linux commands, such as grep, sed, and awk, to search and manipulate text.

1. Dot (.)

   • Matches any single character except a newline.
   • Example: f..e matches file, fate, fuse.

2. Caret (^)

   • Matches the start of a line.
   • Example: ^file matches any line that starts with file.

3. Dollar Sign ($)

   • Matches the end of a line.
   • Example: file$ matches any line that ends with file.

4. Asterisk (*)

   • Matches zero or more of the preceding element.
   • Example: fi*le matches fle, file, fiiile.

5. Plus (+)

   • Matches one or more of the preceding element.
   • Example: fi+le matches file, fiile, but not fle.

6. Question Mark (?)

   • Matches zero or one of the preceding element.
   • Example: fi?le matches fle and file.

7. Square Brackets ([])

   • Matches any one of the enclosed characters.
   • Example: file[123] matches file1, file2, and file3.

8. Parentheses (())

   • Groups patterns.
   • Example: (file)+ matches file, filefile, filefilefile.

1. List all files in the current directory that have a .sh extension.
2. List all files that start with test and have exactly one more character.
3. List all files that start with log and end with a digit between 1 and 3.

1. Use grep to find lines in example.txt that start with error.
2. Use grep to find lines in example.txt that end with success.
3. Use grep to find lines in example.txt that contain the word fail followed by any character and then ed.

Solution 1: Using Wildcards

1. ls *.sh
   

2. ls test?
   

3. ls log[1-3]
   

Solution 2: Using Regular Expressions

1. grep '^error' example.txt
   

2. grep 'success$' example.txt
   

3. grep 'fail.ed' example.txt
   

In this section, we covered the basics of using wildcards and regular expressions in Linux. These tools are essential for efficient file management and text processing. By mastering them, you can perform complex searches and manipulations with ease. In the next section, we will delve into piping and redirection, which will further enhance your command-line skills.