Basic regex in grep in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this grep command?

Given a file fruits.txt with the following lines:

apple
banana
apricot
blueberry
avocado

What is the output of this command?

grep '^a' fruits.txt

A

apple
apricot
avocado

B

apricot
avocado

C

apple
banana
apricot
blueberry
avocado

D

banana
blueberry

💡 Hint

The caret (^) matches the start of a line.

The command grep '^a' selects lines starting with the letter 'a'. So it matches 'apple', 'apricot', and 'avocado'.

💻 Command Output

intermediate

Which lines does this grep command select?

Given a file colors.txt with these lines:

red
blue
green
yellow
black

What lines will this command print?

grep 'e$' colors.txt

A

red
blue
green
yellow
black

B

blue
green

C black

D

red
yellow

💡 Hint

The dollar sign ($) matches the end of a line.

The command grep 'e$' selects lines ending with 'e'. 'blue' and 'green' end with 'e'.

💻 Command Output

advanced

What is the output of this grep command with character classes?

Given a file words.txt containing:

cat
cot
cut
cit
cet

What lines will this command print?

grep 'c[aeiou]t' words.txt

A

cat
cot
cut
cet

B

cat
cot
cut

C

cat
cot
cut
cit
cet

D

cat
cot
cut
cit

💡 Hint

The pattern matches 'c' followed by a vowel, then 't'.

The pattern c[aeiou]t matches words with 'c', followed by a vowel (a,e,i,o,u), then 't'. It matches all lines: 'cat'(a), 'cot'(o), 'cut'(u), 'cit'(i), 'cet'(e).

💻 Command Output

advanced

What error or output does this grep command produce?

What happens when you run this command?

grep '[a-z' file.txt

A No output, command runs silently

B Prints all lines containing any lowercase letter

C Syntax error: missing closing bracket in regex

D Prints lines containing the exact string '[a-z'

💡 Hint

Unclosed character classes are treated literally by grep.

Because the character class is not closed, grep treats the pattern as a literal string '[a-z'. So it prints lines containing that exact substring.

🧠 Conceptual

expert

How many lines does this grep command select?

Given a file data.txt with these lines:

123abc
abc123
abc
123
ab123cd
xyz

How many lines will this command print?

grep -E '^[0-9]+[a-z]+$' data.txt

A 1

B 2

C 3

D 0

💡 Hint

The pattern means: start with one or more digits, then one or more lowercase letters, and nothing else.

Only the line '123abc' matches the pattern: it starts with digits and ends with letters, with no extra characters.