A directory holds file1.txt, file2.txt and file10.txt. Which glob pattern matches the first two but not file10.txt?
LPIC-1 Exam 101-500, objective 103. GNU and Unix commands easy
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How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Correct file?.txt
Correct. ? matches exactly one character, so the pattern requires a single character between file and .txt. file10.txt has two and is excluded.
Not correct file*.txt
Wrong. * matches any string including the empty one, so it matches all three names — and file.txt as well, if it existed.
Not correct file[0-9]*.txt
Wrong. The bracket matches the 1, and the * then matches the remaining 0, so file10.txt is included.
Not correct file[0-9][0-9].txt
Wrong, and it inverts the result: it demands exactly two digits, so it matches only file10.txt.
Why
Pathname expansion is done by the shell before the command runs and uses three metacharacters: * for any string including the empty one, ? for exactly one character, and [...] for one character from a set or range, with a leading ! or ^ inside the brackets negating it. A pattern that matches nothing is passed through unchanged by default, which is why a failed glob often reaches the command as literal text.
Where this comes from
- Cited
- manual page glob(7)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 103 and space the ones you get wrong.
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