wildcard.md

Wildcards in Linux

Wildcards are special characters used in Linux to represent unknown or variable values in filenames and commands. They allow users to efficiently search for, list, and manipulate multiple files at once without having to type each name explicitly. Wildcards are primarily used in conjunction with commands like ls, cp, mv, and rm, making file management more efficient.

Types of Wildcards in Linux

1. Asterisk (*) – Matches Any Number of Characters

The asterisk (*) is the most commonly used wildcard in Linux. It represents zero or more characters in a filename or directory. This means that it can match multiple files at once, regardless of the characters in their names.

• Example:

  ls *.txt

  This command lists all files in the current directory that end with .txt.

• Another Example:

  rm file*

  This removes all files that start with "file", such as file1.txt, file2.txt, or file_document.txt.

2. Question Mark (?) – Matches Exactly One Character

The question mark (?) is used when a single character in a filename is unknown or variable. It matches exactly one character, making it useful for filtering files with slight differences in their names.

• Example:

  ls file?.txt

  This lists files like file1.txt, fileA.txt, and fileB.txt but not file12.txt because ? only replaces a single character.

3. Square Brackets ([]) – Matches Any Single Character from a Set

Square brackets ([]) allow users to specify a set of possible characters to match in a filename. It replaces exactly one character but only with characters listed inside the brackets.

• Example:

  ls file[123].txt

  This matches file1.txt, file2.txt, and file3.txt but not file4.txt.

• Range Example:

  ls file[a-c].txt

  This matches filea.txt, fileb.txt, and filec.txt but not filed.txt.

4. Exclamation Mark (! or ^ Inside []) – Negation in Character Sets

By adding an exclamation mark (!) or caret (^) inside square brackets, users can exclude certain characters instead of including them.

• Example:

  ls file[!123].txt

  This matches any fileX.txt where X is not 1, 2, or 3.

5. Curly Braces ({}) – Expands Multiple Options

Curly braces ({}) are not traditional wildcards but are used for brace expansion, allowing users to specify multiple options at once.

• Example:

  echo {file1,file2,file3}.txt

  This expands to file1.txt file2.txt file3.txt.

• Range Example:

  echo {1..5}

  This expands to 1 2 3 4 5.

6. Double Asterisk (**) – Recursive Matching (Bash 4.0+)

In newer versions of Bash (4.0+), enabling globstar allows the use of **, which searches recursively through directories.

• Example:

  shopt -s globstar  # Enable globstar if not already enabled
  ls **/*.txt

  This lists all .txt files in the current directory and all its subdirectories.