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When working in the shell, special characters like ?, *, and [ ] are interpreted by the globbing engine for filename matching. Preceding these characters with a backslash (\) or quoting them forces the shell to treat them as literal characters.
Using an escape (\) or quotes disables globbing for the next character or entire string. This gives you precise control over filename creation and listing.

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1. Creating Sample Files

First, generate files whose names differ only by the first letter: 
$ touch sail hail mail fail tail
$ ls
fail hail mail sail tail

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2. Wildcard vs. Literal ?

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2.1 Using the ? Wildcard

The ? matches exactly one character. Attempting to create ?ail without escaping: 
$ touch ?ail
$ ls
fail hail mail sail tail
No new file appears because ?ail expanded to all existing matches (fail, hail, etc.).

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2.2 Escaping ? for Literal Filenames

To create a file literally named ?ail: 
$ touch \?ail
$ ls
?ail fail hail mail sail tail

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3. Listing Files with a Leading ?

You can retrieve the ?ail file by escaping or quoting the pattern: 
$ ls \?ail
?ail

$ ls "?ail"
?ail
Both methods disable globbing and match the literal filename.

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4. Mixing Literals and Wildcards

Assume these files exist: 
$ touch hail fail mail \?ail
$ touch hailTwo failTwo mailTwo \?ailTwo
$ ls
?ail ?ailTwo fail failTwo hail hailTwo mail mailTwo
To list all files starting with a literal ?ail: 
$ ls \?ail*
?ail  ?ailTwo
Here, \?ail* treats \? as literal ? and * as the wildcard for any suffix.
Be cautious: unescaped wildcards can match unintended files. Always check your patterns with echo or ls before running destructive commands.

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5. Merging Globs into a Single Pattern

For files named Pail, Pail*, and PailTwo: 
$ touch Pail Pail* PailTwo
$ ls
Pail Pail* PailTwo
You can match them all using: 
$ ls Pail*
Pail Pail* PailTwo
The * wildcard expands to zero or more characters following Pail.

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6. Quick Reference Table

Special CharacterBehaviorEscaped FormExample
?Single-character match\?touch \?file
*Zero or more characters\*ls Pail\*
[ ]Character set\[ \]ls \[abc\]*

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Summary

  • A backslash (\) or quotes disables globbing for the next character or entire string.
  • Use wildcards (?, *, [ ]) without escaping to match patterns.
  • Combine escaped literals and wildcards for precise filename operations.

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