Wildcards & Globbing in Linux: A Deep CLI Guide

A practical, system-level guide to understanding wildcards (globbing) in the Linux command line — how globbing really works, how shells differ, and the pitfalls worth knowing.

What wildcards really are

Wildcards are pattern-matching characters expanded by the shell itself, not by commands like ls, cp, or rm.

ls *.txt

What actually happens:

shell expands *.txt → file1.txt file2.txt
ls file1.txt file2.txt

Commands never see wildcards — they only receive expanded filenames.

Globbing vs. regular expressions

Example confusion:

ls .*txt        # glob
ls | grep .*txt # regex

Expansion order (important)

Shell expansion happens in a defined order: brace expansion {} → tilde expansion ~ → parameter expansion $VAR → command substitution $( ) → pathname expansion (globbing) → quote removal. This affects correctness and safety.

Types of wildcards

Asterisk *

Matches zero or more characters, and does not cross directory separators (/).

*.log
backup*

Question mark ?

Matches exactly one character.

file?.txt   # file1.txt matches | file10.txt does not

Character classes [ ]

file[1-3].txt
file[a-z].txt
file[!0-9].txt   # NOT digits

Brace expansion {} (not a wildcard!)

Brace expansion generates strings before globbing.

echo file{1,2,3}.txt

file1.txt file2.txt file3.txt

Ranges:

echo {a..d}
echo {01..10}

Advanced globbing patterns

Enable extended globbing:

shopt -s extglob

*.!(txt)      # anything except txt
*@(jpg|png)

Requires Bash or Zsh.

Hidden files and dotfiles

* does NOT match .hidden. .* matches dotfiles, but also . and ...

Safe pattern:

ls .[^.]*

Recursive globbing **

shopt -s globstar
ls **/*.c

Conceptually equivalent to:

find . -name "*.c"

Wildcards with common commands

cp *.txt /backup/
rm report[0-9].txt
mv *.log old_logs/
chmod +x *.sh

Always test first:

echo rm *.log

Wildcards vs. find

Use globs for simple cases, find for complex logic.

Quoting & escaping

Disable expansion completely:

echo "*.txt"

Escape a single wildcard:

echo \*.txt

Why it matters:

rm "$file"

Safety techniques (very important)

Dry-run everything:

echo rm *.log

Fail on no matches:

shopt -s failglob

Prevent dangerous deletes:

rm -- -file.txt

Performance considerations

Globbing happens before execution; large directories mean memory expansion cost. Use find for thousands of files.

getconf ARG_MAX

Shell differences

Real-world use cases

# Cleanup logs
rm /var/log/*.{1,old}

# Project setup
mkdir -p app/{src,bin,docs,tests}

# Batch rename preview
echo mv *.jpeg *.jpg

Common mistakes

Believing commands interpret wildcards, forgetting hidden files, mixing regex with glob syntax, and unquoted variables.

Exercises

Beginner:

ls *.txt

Intermediate:

find . -name "*.log" -mtime -3

Advanced:

shopt -s globstar extglob
ls **/*.!(*.tmp)

Understanding globbing gives you precision, safety, and speed at the command line.