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In this lesson, we dive into how the ? wildcard works in glob patterns. In Bash and most shells, ? matches exactly one character, so the filenames must align in length with your pattern. This enables precise control over file selection by combining fixed text and single-character placeholders.

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? Wildcard Basics

  • ? replaces exactly one character.
  • Does not match zero characters.
  • Treats the dot (.) as an actual character (unless dotglob is enabled).
The ? wildcard differs from *, which matches zero or more characters. Use ? when you need strict length matching.

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Example 1: Single Character Prefix Before “ail”

Assume the directory contains:
rail, Document.doc, fail, hail, bar, sail, foo, mail, 4ail, foobar.
The image shows a list of words with checkmarks and crosses, indicating matches and non-matches for a pattern "ail" with different prefixes. It illustrates the concept of expansion globs.
Use ?ail to match any single-character prefix followed by ail: 
$ ls
rail  Document.doc  fail  hail  bar  sail  foo  mail  4ail  foobar

$ ls ?ail
rail  fail  hail  sail  mail  4ail
  • ? matches one character (r, f, h, s, m, 4).
  • ail anchors the suffix.

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Example 2: “tes” + Two Characters + “.txt”

Directory listing:
test.sh, file.txt, tes1t.txt, test2.txt, file1.txt.
The image illustrates the concept of expansion globs, showing a list of filenames with checkmarks and crosses indicating matches to the pattern "tes??.txt".
With the pattern tes??.txt: 
$ ls
test.sh  file.txt  tes1t.txt  test2.txt  file1.txt

$ ls tes??.txt
tes1t.txt  test2.txt
  • tes fixes the first three letters.
  • ?? matches exactly two characters (1t, 2.).
  • .txt matches the file extension.

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Example 3: “test” + One Character + “.txt”

Consider these files:
test1-2.txt, tes1t.txt, test2.txt, test3.sh, test1.txt, file1.txt.
The image illustrates file name matching using expansion globs, showing which files match the pattern "test?.txt" with checkmarks and crosses.
Use test?.txt to find files with a single character after test and before .txt: 
$ ls
test1-2.txt  tes1t.txt  test2.txt  test3.sh  test1.txt  file1.txt

$ ls test?.txt
test1.txt  test2.txt
  • test anchors the prefix.
  • ? matches one character (1, 2).
  • .txt ensures the extension.

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Example 4: One Character + “est.” + Three Characters

Matching pattern ?est.??? to include any one-character prefix, est., and exactly three characters as the extension: 
$ ls
test.txt  vest.txt  test.jpg  file.sh  rest.txt  west.doc

$ ls ?est.???
test.txt  vest.txt  test.jpg  rest.txt  west.doc
  • ?est allows any single first character.
  • The . after est is literal.
  • ??? requires exactly three-character extension.

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Example 5: Exactly Four-Character Filenames

Directory content:
1234, abcd, kei5, some_file.txt, x0f4p, 90c1, dir, keio5, touch, x0fp.
The image shows a list of strings with checkmarks and crosses, indicating which strings match a certain pattern, and a column of matching strings on the right. The title is "Expansion Globs," suggesting a demonstration of pattern matching.
Pattern ???? finds names exactly four characters long: 
$ ls
1234  abcd  kei5  some_file.txt  x0f4p  90c1  dir  keio5  touch  x0fp

$ ls ????
1234  abcd  kei5  90c1  x0fp
  • Four ? must each match one character.
  • Filters out any name not exactly four characters.

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Conclusion

Using the ? wildcard in your glob patterns helps you precisely filter filenames by length and content. Combine fixed text with ? placeholders to tailor your matches exactly.
Ensure you enable dotglob if you want to include hidden files in matches: 
shopt -s dotglob

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