File download automation in Bash Scripting - Step-by-Step Execution

Concept Flow - File download automation

Start script

↓

Set URL variable

↓

Run download command

↓

Check download success?

No→Show error message

Yes↓

File saved locally

↓

End

The script sets the URL, runs the download command, checks if it succeeded, then saves the file locally or shows an error.

Execution Sample

Bash Scripting

url="https://example.com/file.txt"
curl -O "$url"
if [ $? -eq 0 ]; then
  echo "Download succeeded"
else
  echo "Download failed"
fi

This script downloads a file from a URL and reports if the download succeeded or failed.

Execution Table

Step	Action	Command/Check	Result	Output
1	Set URL variable	url="https://example.com/file.txt"	url set
2	Run download command	curl -O "$url"	Download attempt	File saved as file.txt or error
3	Check download success	if [ $? -eq 0 ]	Success or failure	Determines next step
4	If success	echo "Download succeeded"	Print message	Download succeeded
5	If failure	echo "Download failed"	Print message	Download failed

💡 Script ends after printing success or failure message

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
url	unset	https://example.com/file.txt	https://example.com/file.txt	https://example.com/file.txt
$?	unset	unset	0 or non-zero	0 or non-zero

Key Moments - 3 Insights

Why do we check the value of $? after the curl command?

Because $? holds the exit status of the last command. Checking if it equals 0 tells us if curl succeeded (see execution_table step 3).

What does the -O option in curl do?

It tells curl to save the file with its original name from the URL, so the file is saved locally automatically (see execution_table step 2).

What happens if the URL is wrong or unreachable?

Curl will fail, $? will be non-zero, and the script will print "Download failed" (see execution_table step 5).

Visual Quiz - 3 Questions

Look at the execution table, what does the variable $? represent at step 3?

A The URL string

B The exit status of the curl command

C The name of the downloaded file

D The number of bytes downloaded

💡 Hint

Check the 'Command/Check' and 'Result' columns at step 3 in the execution_table.

At which step does the script decide if the download succeeded or failed?

A Step 3

B Step 2

C Step 4

D Step 5

💡 Hint

Look at the 'Check download success' action in the execution_table.

If the URL variable was empty, what would happen in the execution table?

A Curl would download the file successfully

B The script would skip the download

C Curl would fail, and the script prints 'Download failed'

D The script would print 'Download succeeded' without downloading

💡 Hint

Think about what happens if curl has no valid URL to download (see variable_tracker and step 5).

Concept Snapshot

File download automation in bash:
- Set URL variable: url="https://example.com/file.txt"
- Use curl -O "$url" to download file with original name
- Check $? for success (0 means success)
- Print message based on success or failure
- Automates file download with simple script

Full Transcript

This script automates downloading a file using bash. First, it sets a variable 'url' with the file's web address. Then it runs 'curl -O' with that URL to download the file and save it locally with the same name. After the download command, it checks the special variable '$?' which holds the exit status of the last command. If '$?' equals 0, it means the download succeeded, so the script prints 'Download succeeded'. Otherwise, it prints 'Download failed'. This simple flow helps automate file downloads and handle errors gracefully.