File globbing (wildcards *, ?, []) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What files match this pattern?

Given a directory containing files:
report1.txt, report2.txt, report_final.txt, summary.txt, data.csv
What files will match the pattern report?.txt?

A report1.txt, report2.txt, report_final.txt

B report1.txt, report2.txt

C report_final.txt

D summary.txt, data.csv

💡 Hint

The question mark matches exactly one character.

The pattern report?.txt matches files starting with 'report', followed by exactly one character, then '.txt'. So it matches 'report1.txt' and 'report2.txt' but not 'report_final.txt' because it has more than one character after 'report'.

💻 Command Output

intermediate

Which files match the pattern with brackets?

In a folder with files: data1.csv, data2.csv, data3.csv, dataA.csv, dataB.csv
Which files match the pattern data[12].csv?

A data1.csv, data2.csv, data3.csv

B data3.csv

C dataA.csv, dataB.csv

D data1.csv, data2.csv

💡 Hint

Square brackets match exactly one character from the set inside.

The pattern data[12].csv matches files where the character after 'data' is either '1' or '2'. So it matches 'data1.csv' and 'data2.csv' only.

📝 Syntax

advanced

Identify the correct glob pattern for matching files ending with .log or .txt

Which of the following patterns correctly matches files that end with either .log or .txt?

A *.{log,txt}

B *.[log|txt]

C *.[log,txt]

D *.(log|txt)

💡 Hint

Brace expansion is used to match multiple extensions.

The pattern *.{log,txt} uses brace expansion to match files ending with either '.log' or '.txt'. The other options use invalid syntax for globbing.

💻 Command Output

advanced

What is the output of this glob pattern?

Given files: file1.txt, file2.txt, file10.txt, file20.txt, fileA.txt
What files match the pattern file?.txt?

A file1.txt, file2.txt, fileA.txt

B file1.txt, file2.txt

C file10.txt, file20.txt

D fileA.txt

💡 Hint

The question mark matches exactly one character.

The pattern file?.txt matches files with exactly one character after 'file' before '.txt'. So it matches 'file1.txt', 'file2.txt', and 'fileA.txt'. It does not match 'file10.txt' or 'file20.txt' because they have two characters after 'file'.

🧠 Conceptual

expert

How many files match this complex pattern?

In a directory with files: a1.txt, a2.txt, a10.txt, b1.txt, b2.txt, c1.txt
How many files match the pattern [ab]?*.txt?

A 3

B 4

C 5

D 6

💡 Hint

The pattern matches files starting with 'a' or 'b', followed by at least one character, then any characters, ending with '.txt'.

The pattern [ab]?*.txt matches files starting with 'a' or 'b', then at least one character (due to '?'), then zero or more characters (due to '*'), ending with '.txt'. The matched files are: a1.txt, a2.txt, a10.txt, b1.txt, b2.txt. The file c1.txt does not match because it starts with 'c'. So total matched files are 5.

Practice

1. Which wildcard pattern matches all files with any extension starting with log in their name?

easy

A. log* only matches files named exactly 'log'

B. log?

C. log[0-9]

D. log*

Solution

1. Step 1: Understand the wildcard *

   The * matches zero or more characters, so log* matches any file starting with 'log' followed by anything or nothing.

2. Step 2: Compare other options

   log? matches 'log' plus exactly one character, log[0-9] matches 'log' plus one digit, and the last option is incorrect about log*.

3. Final Answer:

   log* -> Option D

4. Quick Check:

   Wildcard * matches any characters [OK]

Hint: Use * to match any number of characters [OK]

Common Mistakes:

• Confusing * with ? wildcard
• Thinking * matches only one character
• Misunderstanding [] as matching multiple characters

2. Which of the following is the correct pattern to match files named data1, data2, but not data10?

easy

A. data?

B. data*

C. data[1-9]

D. data??

Solution

1. Step 1: Understand the pattern data[1-9]

   This matches 'data' followed by exactly one digit from 1 to 9, so it matches 'data1' and 'data2' but not 'data10'.

2. Step 2: Check other patterns

   data? matches 'data' plus any one character (including letters), data* matches 'data' plus any characters (including 'data10'), and data?? matches 'data' plus exactly two characters (so it matches 'data10').

3. Final Answer:

   data[1-9] -> Option C

4. Quick Check:

   Square brackets match one character from set [OK]

Hint: Use [ ] to match one character from a range [OK]

Common Mistakes:

• Using * which matches too many files
• Using ? which matches any single character, not range
• Confusing number of characters matched

3. Given files: file1.txt, file2.txt, fileA.txt, fileB.txt, what files does the pattern file?.txt match?

medium

A. file1.txt, file2.txt

B. file1.txt, file2.txt, fileA.txt, fileB.txt

C. fileA.txt, fileB.txt

D. file.txt

Solution

1. Step 1: Understand the pattern file?.txt

   The ? matches exactly one character, so it matches any file named 'file' plus one character plus '.txt'.

2. Step 2: Check which files match

   All files with names 'file1.txt', 'file2.txt', 'fileA.txt', and 'fileB.txt' have exactly one character after 'file' before '.txt', so all match.

3. Final Answer:

   file1.txt, file2.txt, fileA.txt, fileB.txt -> Option B

4. Quick Check:

   ? matches exactly one character [OK]

Hint: Use ? to match exactly one character [OK]

Common Mistakes:

• Thinking ? matches zero or multiple characters
• Confusing ? with *
• Ignoring file extension in pattern

4. You want to list files named report1, report2, and report3 only. Which pattern is incorrect?

medium

A. report*

B. report?

C. report[1-3]

D. report[123]

Solution

1. Step 1: Analyze pattern report*

   This matches 'report' plus any characters, so it matches more than just 'report1', 'report2', and 'report3'. It includes 'report10', 'report_final', etc.

2. Step 2: Check other patterns

   report[1-3] and report[123] match exactly one character from 1,2,3 after 'report'. report? matches 'report' plus any one character, which includes 'report1', 'report2', 'report3' but also others with one character.

3. Final Answer:

   report* -> Option A

4. Quick Check:

   * matches too many files [OK]

Hint: Use [] to limit characters, * matches too many [OK]

Common Mistakes:

• Using * when exact matches needed
• Assuming ? limits to digits only
• Not realizing [] matches one character only

5. You have files: img01.png, img02.png, img10.png, img20.png. Which pattern matches only files with numbers from 01 to 09?

hard

A. img0[1-9].png

B. img[0-9][1-9].png

C. img??.png

D. img[01-09].png

Solution

1. Step 1: Understand pattern img0[1-9].png

   This matches 'img0' plus one digit from 1 to 9, then '.png'. So it matches 'img01.png' to 'img09.png'.

2. Step 2: Check other patterns

   img[0-9][1-9].png matches any two digits, including 'img10.png' and 'img20.png'. img??.png matches any two characters after 'img', so all files. img[01-09].png is invalid syntax because ranges like '01-09' are not valid inside [].

3. Final Answer:

   img0[1-9].png -> Option A

4. Quick Check:

   Use 0 then [1-9] for numbers 01-09 [OK]

Hint: Use fixed digit then range in [] for number ranges [OK]

Common Mistakes:

• Using invalid range syntax inside []
• Using ?? which matches any two characters
• Not fixing leading zero for 01-09