xargs for building commands from input in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this xargs command?

Given a file names.txt containing:

alice
bob
carol

What is the output of:

cat names.txt | xargs -I {} echo Hello, {}

Linux CLI

cat names.txt | xargs -I {} echo Hello, {}

A

Hello, alice
Hello, bob
Hello, carol

B Hello, alice bob carol

C

Hello, alice
bob
carol

D Hello, alice Hello, bob Hello, carol

💡 Hint

Remember that xargs runs the command once per input line when using -I.

The -I option replaces {} with each line from input and runs the command separately once per line. Each echo outputs 'Hello, ' followed by a newline, producing three lines.

💻 Command Output

intermediate

How many files are deleted by this command?

Assuming the current directory has files: file1.txt, file2.txt, file3.txt, what does this command do?

ls *.txt | xargs rm

How many files are deleted?

Linux CLI

ls *.txt | xargs rm

A 1

B 3

C 0

D Depends on xargs version

💡 Hint

xargs passes all arguments to rm in one go unless limited.

The ls command lists all .txt files, and xargs passes all filenames to rm at once, deleting all 3 files.

🔧 Debug

advanced

Why does this xargs command fail?

Consider this command:

echo "one two three" | xargs echo

It outputs:

one two three

instead of:

one
two
three

Why?

Linux CLI

echo "one two three" | xargs echo

A Because the shell merges all output into one line

B Because echo does not accept multiple arguments

C Because xargs -n 1 is ignored when input is from echo

D Because echo outputs all arguments on one line, xargs runs echo once with all words

💡 Hint

Check how echo behaves with multiple arguments.

xargs runs echo once with all words as arguments. echo prints all arguments on one line separated by spaces.

📝 Syntax

advanced

Which xargs command correctly replaces {} with input lines?

You want to run mv on files listed in files.txt, renaming each by adding .bak. Which command works?

A cat files.txt | xargs -i mv {} {}.bak

B cat files.txt | xargs mv {} {}.bak

C cat files.txt | xargs -I {} mv {} {}.bak

D cat files.txt | xargs -I mv {} {}.bak

💡 Hint

The placeholder {} must be specified with -I option.

Option C uses -I {} correctly to replace {} with each input line. Option C uses -i which is deprecated and requires lowercase i with no argument, but may not work on all systems. Options B and D have syntax errors.

🚀 Application

expert

How to safely delete files with spaces using xargs?

You have a file list.txt containing filenames, some with spaces, e.g., my file.txt. Which command safely deletes all files listed?

A cat list.txt | tr '\n' '\0' | xargs -0 rm

B cat list.txt | xargs -I {} rm {}

C cat list.txt | xargs rm

D cat list.txt | xargs -d '\n' rm

💡 Hint

Use null character as separator to handle spaces in filenames.

Option A uses null character as delimiter with -0 option, which safely handles filenames with spaces. Option A uses -d '\n' which may not be supported everywhere. Option A breaks on spaces. Option A runs rm once per file but may break on spaces without proper quoting.