Anchors (^, $) in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this grep command?

Given a file data.txt with the following lines:

apple
application
pineapple
snapple
apple pie

What is the output of this command?

grep '^apple$' data.txt

Bash Scripting

grep '^apple$' data.txt

A

apple
application
apple pie

B

apple
apple pie

C apple

D apple pie

💡 Hint

The ^ anchor matches the start of the line, and $ matches the end of the line.

The pattern '^apple$' matches lines that contain exactly 'apple' with nothing before or after. So only the line 'apple' matches.

💻 Command Output

intermediate

Which lines does this grep command print?

Given a file log.txt with these lines:

error: file not found
warning: low disk space
error: access denied
info: update complete

What lines will this command print?

grep '^error:' log.txt

Bash Scripting

grep '^error:' log.txt

A error: access denied

B

error: file not found
error: access denied

C

error: file not found
warning: low disk space
error: access denied

D

file not found
access denied

💡 Hint

The ^ anchor matches the start of the line, so only lines starting with 'error:' are matched.

Lines starting exactly with 'error:' are matched. So the two error lines are printed.

📝 Syntax

advanced

Which grep pattern matches lines ending with '.txt'?

You want to find lines in a file that end exactly with '.txt'. Which grep pattern is correct?

A grep '^txt$' filename

B grep '^\.txt' filename

C grep '\.txt' filename

D grep '\.txt$' filename

💡 Hint

The $ anchor matches the end of the line. The dot must be escaped to match a literal dot.

Pattern '\.txt$' matches lines ending with '.txt'. '^\.txt' matches lines starting with '.txt'. '\.txt' matches anywhere. '^txt$' matches lines exactly 'txt'.

🔧 Debug

advanced

Why does this grep command not match any lines?

You run this command:

grep '^error$' log.txt

But no lines are printed, even though the file has lines starting with 'error:'. Why?

A Because '^error$' matches lines exactly equal to 'error', but lines have 'error:' with colon.

B Because '^error$' matches lines starting with 'error' but not ending with it.

C Because grep needs -E option to use anchors.

D Because the file is empty.

💡 Hint

Check if the lines exactly match the pattern or have extra characters.

The pattern '^error$' matches lines that are exactly 'error'. Lines like 'error:' have extra characters and do not match.

🚀 Application

expert

How many lines match this grep pattern?

Given a file words.txt with these lines:

cat
concatenate
scatter
cater
act

How many lines will this command print?

grep '^cat$' words.txt

A 1

B 3

C 2

D 0

💡 Hint

The pattern matches lines exactly equal to 'cat'.

Only the line 'cat' matches exactly. Other lines contain 'cat' but have extra letters.