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In earlier lessons, we explored Bash parameter expansion—using operators like # and % (and their double variants ##/%%) to strip prefixes and suffixes from variable values. We even combined these with the wildcard * to broaden matches.
The image is a chart explaining different globbing patterns in programming, showing symbols like #, %, ##, %%, and * with their respective functions.
Globs (also called wildcards or pathname expansion patterns) differ from parameter expansion. They operate directly on filenames and strings in the shell, not on variable values.

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What Are Globs?

Globs let you match file and directory names—or any arbitrary strings—using a concise pattern syntax. They’re simpler than regular expressions (no lookahead, named groups, etc.), but cover most everyday use cases:
Glob PatternMatchesExample
*Zero or more characters*.txt
?Exactly one characterfile?.sh
[abc]Exactly one of the set (a, b, c)report[12].pdf

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When to Use Globs vs. Regex

FeatureGlobsRegular Expressions
SimplicityVery easy to writeMore complex (advanced syntax)
Common Use CaseFile matchingText parsing, validation
Advanced ConstructsNot supportedLookahead, named groups, etc.

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Learning Approach

To master globs, follow these steps:
  1. Gather Sample Strings
    Assemble a broad list of filenames or test strings you need to match.
  2. Identify Common Patterns
    Group similar strings to pinpoint shared prefixes, suffixes, or character sets.
  3. Select the Appropriate Glob
    Choose from *, ?, or bracket expressions ([ ]) to cover your pattern.
  4. Test with Shell Commands
    Run a command like ls or echo to verify that your glob matches the intended files:
# Matches all .log files starting with "app"
ls app*.log
If the output aligns with your expectations, your glob is correct!

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Next Steps

In the following sections, we’ll apply these principles to real-world examples—filtering logs, batch-renaming files, and more. Let’s start by examining a directory of mixed files and crafting precise globs for each case.

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