File download automation in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this wget command?

You run this command in a terminal:

wget -q --show-progress https://example.com/file.txt -O downloaded.txt && echo "Done"

What will be printed on the terminal?

Bash Scripting

wget -q --show-progress https://example.com/file.txt -O downloaded.txt && echo "Done"

A No output at all

B Progress bar showing download progress

C Done

D Error message about missing file

💡 Hint

The -q option means quiet, but --show-progress overrides some quietness.

https://example.com/file.txt returns 404 Not Found, so wget exits non-zero and "Done" is not printed. -q suppresses error messages, and --show-progress does not show progress if the download fails immediately.

📝 Syntax

intermediate

Which script correctly downloads multiple files in a loop?

You want to download files from URLs stored in a file named urls.txt, one URL per line. Which script snippet correctly downloads each file using curl?

A for url in $(cat urls.txt); do curl -O "$url"; done

B while read url; do curl -O "$url"; done < urls.txt

C cat urls.txt | for url in $urls.txt; do curl -O "$url"; done

D for url in urls.txt; do curl -O "$url"; done

💡 Hint

Think about how to read lines safely from a file in bash.

Option B uses a while read loop to read each line safely from the file. Option B splits on spaces which can break URLs with spaces. Option B is invalid syntax. Option B treats the filename as a URL.

🔧 Debug

advanced

Why does this script fail to download files correctly?

Consider this script:

urls=("http://site.com/file 1.txt" "http://site.com/file2.txt")
for url in "${urls[@]}"; do
  curl -O "$url"
done

It fails to download the first file. What is the problem?

Bash Scripting

urls=("http://site.com/file 1.txt" "http://site.com/file2.txt")
for url in "${urls[@]}"; do
  curl -O "$url"
done

A The space in the URL is not encoded, causing curl to fail.

B The array syntax is wrong; it should use single quotes.

C The for loop syntax is invalid; it needs a semicolon after do.

D curl cannot handle URLs with numbers.

💡 Hint

Spaces in URLs must be encoded as %20.

curl fails because the URL contains a space character which is invalid in URLs. It should be encoded as %20 to work properly.

🚀 Application

advanced

How to automate retrying downloads on failure?

You want a bash script that tries to download a file with curl up to 3 times if it fails. Which snippet achieves this?

A curl -O http://example.com/file.txt; if [ $? -ne 0 ]; then curl -O http://example.com/file.txt; fi

B curl -O http://example.com/file.txt || curl -O http://example.com/file.txt || curl -O http://example.com/file.txt

C for i in {1..3}; do curl -O http://example.com/file.txt && break; done

D while curl -O http://example.com/file.txt; do break; done

💡 Hint

Use a loop with a break on success.

Option C tries up to 3 times and stops if curl succeeds. Option C tries sequentially but is less clear. Option C loops only if curl succeeds, so it breaks immediately. Option C tries only twice and no loop.

🧠 Conceptual

expert

What is the best way to download files securely in a script?

You want to automate file downloads in bash but ensure the files are not tampered with. Which approach is best?

A Download files and trust the source without verification.

B Use wget with --no-check-certificate to avoid SSL errors.

C Download files only over HTTP to avoid SSL overhead.

D Download files with curl and then verify their SHA256 checksum against a trusted value.

💡 Hint

Think about verifying file integrity after download.

Verifying the checksum ensures the file is exactly what you expect and not tampered with. Ignoring SSL or using HTTP is insecure.

Practice

1. What is the main purpose of automating file downloads in bash scripting?

easy

A. To slow down the internet speed

B. To make files larger

C. To save time and reduce manual errors

D. To delete files automatically

Solution

1. Step 1: Understand automation benefits

   Automating repetitive tasks like file downloads saves time and reduces mistakes.

2. Step 2: Identify the correct purpose

   The main goal is efficiency and accuracy, not file size or deletion.

3. Final Answer:

   To save time and reduce manual errors -> Option C

4. Quick Check:

   Automation = Save time & reduce errors [OK]

Hint: Automation means doing tasks faster and safer [OK]

Common Mistakes:

• Thinking automation changes file size
• Confusing automation with file deletion
• Assuming automation slows internet

2. Which of the following is the correct syntax to download a file using wget in bash?

easy

A. curl -download http://example.com/file.txt

B. download http://example.com/file.txt

C. fetch http://example.com/file.txt

D. wget http://example.com/file.txt

Solution

1. Step 1: Recall wget command syntax

   The basic wget command to download a file is 'wget URL'.

2. Step 2: Compare options

   Only wget http://example.com/file.txt uses the correct wget syntax; others use invalid commands.

3. Final Answer:

   wget http://example.com/file.txt -> Option D

4. Quick Check:

   wget URL = correct syntax [OK]

Hint: Use 'wget URL' to download files simply [OK]

Common Mistakes:

• Using non-existent commands like 'download' or 'fetch'
• Mixing curl options with wget
• Forgetting to specify the URL

3. What will be the output of this bash command?

curl -O https://example.com/sample.txt
ls | grep sample.txt

medium

A. sample.txt

B. No output

C. curl: command not found

D. Error: file not found

Solution

1. Step 1: Understand curl -O behavior

   The command downloads 'sample.txt' to the current directory.

2. Step 2: Check the ls and grep output

   Listing files and filtering for 'sample.txt' will show the filename if download succeeded.

3. Final Answer:

   sample.txt -> Option A

4. Quick Check:

   curl -O downloads file, ls | grep shows filename [OK]

Hint: curl -O saves file; grep finds it in list [OK]

Common Mistakes:

• Assuming curl prints file content
• Expecting no output after download
• Confusing curl errors with normal output

4. Identify the error in this script snippet for downloading a file:

curl -o https://example.com/data.csv

medium

A. URL is incorrect

B. Missing filename after -o option

C. curl cannot download CSV files

D. No error, script is correct

Solution

1. Step 1: Check curl -o usage

   The '-o' option requires a filename to save the download.

2. Step 2: Analyze the command

   The command provides URL but no filename after '-o', causing error.

3. Final Answer:

   Missing filename after -o option -> Option B

4. Quick Check:

   curl -o needs filename [OK]

Hint: Always give filename after curl -o [OK]

Common Mistakes:

• Forgetting filename after -o
• Thinking URL is wrong format
• Believing curl can't download certain file types

5. You want to automate downloading multiple files listed in a text file named urls.txt. Which bash script snippet correctly downloads each file using wget?

hard

A. while read url; do wget "$url"; done < urls.txt

B. for url in urls.txt; do wget $url; done

C. wget -i urls.txt -O output.log

D. cat urls.txt | wget

Solution

1. Step 1: Understand reading lines from file

   The 'while read url; do ... done < urls.txt' reads each line as a URL.

2. Step 2: Check wget usage inside loop

   Using wget "$url" downloads each URL correctly.

3. Step 3: Analyze other options

   'for url in urls.txt; do wget $url; done' treats filename as URL, 'wget -i urls.txt -O output.log' misuses -O option causing all files to overwrite as 'output.log', 'cat urls.txt | wget' pipes incorrectly.

4. Final Answer:

   while read url; do wget "$url"; done < urls.txt -> Option A

5. Quick Check:

   Loop reading lines + wget = correct [OK]

Hint: Use while read loop to process URLs line by line [OK]

Common Mistakes:

• Using for loop directly on filename
• Misusing wget options
• Piping file content directly to wget