Linux CLI 5 🐧 Wildcards

Wildcards are special characters that allow us to select filenames based on character patterns. They’re also called glob patterns — and they’re one of the most powerful features of the command line.

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A Quick Look at the Examples

ls *.txt
ls ?a?.txt
ls [abc]*
ls file{1,2,3}.txt
ls file{1,2}.txt
ls [[:alnum:]]*
ls [![:alpha:]]*
ls *[[:lower:]2]
ls *[23].txt

Pattern	Matches
*.txt	Any file with .txt extension
?a?.txt	3-char name, second char a, .txt
[abc]*	Starts with a, b, or c
file{1,2,3}.txt	file1.txt, file2.txt, file3.txt
file{1,2}.txt	file1.txt, file2.txt
[[:alnum:]]*	Starts with any alphanumeric character
[![:alpha:]]*	Does not start with a letter
*[[:lower:]2]	Ends with lowercase letter or 2
*[23].txt	Ends with 2 or 3 before .txt

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What Are Wildcards?

Wildcards are special characters used by the shell to match filenames based on patterns.

Key points:

• Also called glob patterns
• The shell expands them before the command runs
• Used with commands like ls, cp, mv, rm, find
• Case-sensitive by default

How it works:

ls *.txt
   │
   ▼
Shell expands to: ls file1.txt file2.txt notes.txt
   │
   ▼
ls receives the list of files

Important: The shell, not the command, does the matching. ls never sees the * — it sees the expanded list.

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Wildcard Characters

Wildcard	Meaning	Example	Matches
*	Any number of characters (0 or more)	*.txt	file.txt, a.txt, .txt
?	Exactly one character	?a?.txt	cat.txt, bat.txt
[chars]	Any one character in the set	[abc]*	apple, banana, cherry
[!chars]	Any one character NOT in the set	[!abc]*	dog, fish, zebra
{p1,p2}	Any of the patterns separated by commas	file{1,2}.txt	file1.txt, file2.txt
[a-z]	Any character in the range	[a-c]*	apple, banana, cherry
[[:class:]]	Any character from a character class	[[:digit:]]*	Files starting with a digit

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Basic Wildcards — Detailed

* — Match Any Number of Characters

ls *.txt         # All files ending in .txt
ls file*         # All files starting with "file"
ls *             # All files in current directory
ls a*b           # Files starting with "a" and ending with "b"

Examples:

$ ls
file.txt  file2.txt  notes.txt  script.sh  image.png

$ ls *.txt
file.txt  file2.txt  notes.txt

$ ls file*
file.txt  file2.txt

$ ls *
file.txt  file2.txt  notes.txt  script.sh  image.png

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? — Match Exactly One Character

ls ?.txt         # Single-char files with .txt
ls ?a?.txt       # 3-char names with "a" in middle
ls file?.txt     # file1.txt, fileA.txt — but NOT file10.txt

Examples:

$ ls
a.txt  b.txt  ab.txt  abc.txt  file1.txt  file10.txt

$ ls ?.txt
a.txt  b.txt

$ ls ??*.txt
ab.txt  abc.txt

$ ls file?.txt
file1.txt
# NOT file10.txt — ? matches exactly ONE character

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[chars] — Match Any One Character in the Set

ls [abc]*        # Starts with a, b, or c
ls file[123].txt # file1.txt, file2.txt, file3.txt
ls [a-z]*        # Starts with lowercase letter
ls [A-Z]*        # Starts with uppercase letter
ls [0-9]*        # Starts with digit

Examples:

$ ls
apple.txt  banana.txt  cherry.txt  dog.txt  zebra.txt

$ ls [abc]*
apple.txt  banana.txt  cherry.txt

$ ls [a-c]*
apple.txt  banana.txt  cherry.txt
# Range: a through c

$ ls [ab]*
apple.txt  banana.txt

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[!chars] — Match Any Character NOT in the Set

ls [!abc]*       # Does NOT start with a, b, or c
ls [!0-9]*       # Does NOT start with a digit
ls file[!1].txt  # fileX.txt but not file1.txt

Examples:

$ ls
apple.txt  banana.txt  cherry.txt  dog.txt  zebra.txt

$ ls [!abc]*
dog.txt  zebra.txt
# Excludes apple, banana, cherry

$ ls [!a-c]*
dog.txt  zebra.txt

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{p1,p2} — Brace Expansion (Match Multiple Patterns)

ls file{1,2,3}.txt   # file1.txt file2.txt file3.txt
ls file{1,2}.txt     # file1.txt file2.txt
ls {a,b,c}.txt       # a.txt b.txt c.txt
ls file{1,2}.{txt,md} # file1.txt file1.md file2.txt file2.md

Note: Brace expansion is a shell feature, not a glob. It generates multiple patterns before globbing.

Examples:

$ ls
file1.txt  file2.txt  file3.txt  file4.txt

$ ls file{1,2,3}.txt
file1.txt  file2.txt  file3.txt

$ ls file{1,2}.txt
file1.txt  file2.txt

$ echo file{1,2}.{txt,md}
file1.txt file1.md file2.txt file2.md

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Character Classes

Character classes use the syntax [[:class:]] — they match any character from a predefined category.

Class	Matches	Example
[:alnum:]	Alphanumeric (letters + digits)	[[:alnum:]]*
[:alpha:]	Letters (a-z, A-Z)	[[:alpha:]]*
[:digit:]	Digits (0-9)	[[:digit:]]*
[:lower:]	Lowercase letters (a-z)	[[:lower:]]*
[:upper:]	Uppercase letters (A-Z)	[[:upper:]]*
[:blank:]	Space and tab	—
[:space:]	Whitespace (space, tab, newline)	—
[:punct:]	Punctuation	[[:punct:]]*
[:xdigit:]	Hexadecimal digits (0-9, a-f, A-F)	[[:xdigit:]]*
[:cntrl:]	Control characters	—
[:graph:]	Printable characters (except space)	—
[:print:]	Printable characters (including space)	—

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Character Class Examples

ls [[:alnum:]]*      # Starts with a letter OR digit
ls [[:alpha:]]*      # Starts with a letter
ls [[:digit:]]*      # Starts with a digit
ls [[:upper:]]*      # Starts with an uppercase letter
ls [[:lower:]]*      # Starts with a lowercase letter

Examples:

$ ls
apple.txt  Apple.txt  123file.txt  _file.txt  z.txt  Z.txt

$ ls [[:lower:]]*
apple.txt  z.txt
# Lowercase only

$ ls [[:upper:]]*
Apple.txt  Z.txt
# Uppercase only

$ ls [[:digit:]]*
123file.txt
# Digits only

$ ls [[:alpha:]]*
apple.txt  Apple.txt  z.txt  Z.txt
# Letters only

$ ls [[:alnum:]]*
apple.txt  Apple.txt  123file.txt  z.txt  Z.txt
# Letters and digits

$ ls [![:alpha:]]*
123file.txt  _file.txt
# NOT starting with a letter

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Combining Wildcards

You can combine wildcards for complex patterns:

ls *[23].txt         # Ends with 2 or 3 before .txt
ls *[[:lower:]2]     # Ends with lowercase letter or 2
ls file[0-9][0-9].txt # file followed by two digits
ls [!a-z]*           # Does NOT start with lowercase
ls *.{txt,md,sh}     # Multiple extensions

Examples:

$ ls
file1.txt  file2.txt  file3.txt  file22.txt  file33.txt
notes.md  script.sh  README.md

$ ls *[23].txt
file2.txt  file3.txt  file22.txt  file33.txt

$ ls *[!0-9].txt
# Files whose name (before .txt) ends with a non-digit
file1.txt  file2.txt  file3.txt

$ ls *.{txt,md}
file1.txt  file2.txt  file3.txt  file22.txt  file33.txt
notes.md  README.md

$ ls file[0-9][0-9].txt
file22.txt  file33.txt
# Two digits after "file"

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Complete Example Session

Let’s build a directory and test all patterns:

# 1. Create test files
$ touch file1.txt file2.txt file3.txt file10.txt file22.txt
$ touch apple.txt banana.txt cherry.txt
$ touch notes.md readme.md
$ touch script.sh
$ touch 123file.txt _underscore.txt
$ touch UPPER.txt lower.txt

# 2. List everything
$ ls
123file.txt  UPPER.txt  _underscore.txt  apple.txt  banana.txt
cherry.txt   file1.txt  file2.txt        file3.txt  file10.txt
file22.txt   lower.txt  notes.md         readme.md  script.sh

# 3. Match by extension
$ ls *.txt
123file.txt  UPPER.txt  _underscore.txt  apple.txt  banana.txt
cherry.txt   file1.txt  file2.txt        file3.txt  file10.txt
file22.txt   lower.txt

# 4. Match by prefix
$ ls file*
file1.txt  file2.txt  file3.txt  file10.txt  file22.txt

# 5. Match by single character
$ ls ?.txt
# Single-char files: (none)

$ ls ??*.txt
# 2+ char files: all .txt files

# 6. Match by character set
$ ls [abc]*
apple.txt  banana.txt  cherry.txt

# 7. Brace expansion
$ ls file{1,2,3}.txt
file1.txt  file2.txt  file3.txt

# 8. Character classes
$ ls [[:digit:]]*
123file.txt

$ ls [[:upper:]]*
UPPER.txt

$ ls [![:alpha:]]*
123file.txt  _underscore.txt

# 9. Complex patterns
$ ls *[23].txt
file2.txt  file3.txt  file22.txt

$ ls file[0-9][0-9].txt
file10.txt  file22.txt

# 10. Multiple extensions
$ ls *.{txt,md}
# All .txt and .md files

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Quick Reference

Wildcard Characters

Wildcard	Meaning	Example
*	Any number of characters	*.txt
?	Exactly one character	?.txt
[abc]	Any one of a, b, c	[abc]*
[a-z]	Any in range	[a-z]*
[!abc]	Not a, b, or c	[!abc]*
{a,b}	Brace expansion	file{1,2}.txt

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Character Classes

Class	Matches
[[:alnum:]]	Letters + digits
[[:alpha:]]	Letters
[[:digit:]]	Digits
[[:lower:]]	Lowercase
[[:upper:]]	Uppercase
[[:blank:]]	Space, tab
[[:punct:]]	Punctuation
[[:xdigit:]]	Hex digits

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Common Patterns

Pattern	Matches
*.txt	All .txt files
file*	Files starting with file
*file	Files ending with file
?.txt	Single-char .txt files
??.txt	Two-char .txt files
[abc]*	Starting with a, b, or c
[!0-9]*	Not starting with digit
file{1,2,3}.txt	file1, file2, file3
*[23].txt	Ending in 2 or 3
*.[ch]	.c or .h files

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Best Practices

✅ Do This:

# Test patterns with echo first (safe!)
echo *.txt              # Shows what would be matched
echo file{1,2,3}.txt

# Use ls to verify before destructive operations
ls *.log                # Check first
rm *.log                # Then delete

# Quote patterns when you want literal characters
echo "*"                # Prints *
echo *                  # Expands to filenames

# Use character classes for portability
ls [[:digit:]]*         # More portable than [0-9]*

# Combine for precise matching
ls file[0-9][0-9].txt   # file + 2 digits

❌ Don’t Do This:

# Don't use rm * without checking!
rm *                    # ❌ Deletes EVERYTHING
ls *                    # ✅ Check first

# Don't forget * matches zero characters
ls *.txt                # Also matches ".txt" (if it exists)

# Don't confuse globs with regex
# Globs are for filenames; regex is for text matching
# [!abc] in glob ≠ [^abc] in regex

# Don't use braces for filenames that don't exist
ls file{1,2,3,4,5,6,7,8,9,10}.txt  # Fails if any don't exist

# Don't forget case sensitivity
ls *.TXT                # Different from *.txt on Linux

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Common Pitfalls

Pitfall	Problem	Solution
rm * without checking	Deletes everything	ls * first
Expecting ? to match many	Only matches one	Use * for many
Case sensitivity	*.TXT ≠ *.txt	Watch case
Empty expansion	Pattern matches nothing	Shell passes pattern literally
Quoting too much	"*.txt" won’t expand	Quote only when needed
Forgetting [!...]	Uses [^...] (regex)	Use ! for glob negation

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When to Quote Wildcards

Situation	Use	Example
Want expansion	No quotes	ls *.txt
Want literal character	Single quotes	echo '*.txt'
Want variable expansion	Double quotes	echo "$dir"/*.txt
Pass to find	Quote or escape	find . -name "*.txt"

Examples:

$ touch a.txt b.txt

$ ls *.txt
a.txt  b.txt

$ echo "*.txt"
*.txt                    # Literal — no expansion

$ echo '*.txt'
*.txt                    # Literal — no expansion

$ echo *.txt
a.txt b.txt              # Expanded by shell

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Practical Examples

1. Backup all .conf files

cp /etc/*.conf ~/backup/

2. Delete all temporary files

rm *.tmp
rm *.bak

3. List images by format

ls *.{jpg,png,gif}

4. Find files with 2-digit numbers

ls file[0-9][0-9].txt

5. Rename with brace expansion

mv image.{jpg,jpeg}
# Renames image.jpg → image.jpeg

6. Match multiple extensions

ls *.{c,h}
# All C source and header files

7. Exclude hidden files (which start with .)

ls [!.]*
# Files NOT starting with a dot

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Summary

Wildcard	Meaning	Example
*	Any characters (0+)	*.txt
?	One character	?.txt
[abc]	One of a, b, c	[abc]*
[a-z]	Range	[a-z]*
[!abc]	Not a, b, c	[!abc]*
{1,2}	Brace expansion	file{1,2}.txt
[[:class:]]	Character class	[[:digit:]]*

Key takeaways:

• * is the most common wildcard — matches any number of characters
• ? matches exactly one character
• [...] matches one character from a set or range
• {...} expands to multiple patterns (brace expansion)
• [[:class:]] matches by character category
• ! inside [ ] means “not” (e.g., [!abc])
• Test with echo or ls before running destructive commands
• The shell expands wildcards before the command runs

Remember: Wildcards are one of the most powerful features of the command line. They save you from typing long filenames and let you operate on many files at once. But with great power comes great responsibility — always test with ls first before using rm with wildcards!

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