Scenario

You're troubleshooting a service that produces untagged log output when run manually, making it difficult to analyze timing and sequence of events.

Task

Create a command that reads from standard input line by line and appends the current timestamp to the end of each line as it's read. Test it interactively by piping output to verify it works, then save the solution to a shell script at /usr/local/bin/timestamp.sh and make it executable so it can be used in any pipeline.

Example

# Before (untagged log output)

Application started
Processing request #1234
Database connection established
Request completed

# After (timestamped in real-time)

Application started - 2025-11-06 15:30:45
Processing request #1234 - 2025-11-06 15:30:46
Database connection established - 2025-11-06 15:30:47
Request completed - 2025-11-06 15:30:48

Step 1: Test the timestamp command

date +'%Y-%m-%d %H:%M:%S'

Step 2: Test the one-liner with simple input

echo -e "Line 1\nLine 2\nLine 3" | while read line; do echo "$line - $(date +'%Y-%m-%d %H:%M:%S')"; done

Step 3: Test with time-delayed output to see timestamps change

(echo "Start"; sleep 1; echo "Middle"; sleep 1; echo "End") | while read line; do echo "$line - $(date +'%Y-%m-%d %H:%M:%S')"; done

Step 4: Create the script file

nano /usr/local/bin/timestamp.sh

Add this content:

#!/bin/bash
while IFS= read -r line; do
    echo "$line - $(date +'%Y-%m-%d %H:%M:%S')"
done

Save and exit (Ctrl+O, Enter, Ctrl+X in nano)

Step 5: Make the script executable

chmod +x /usr/local/bin/timestamp.sh

Step 6: Test the script

seq 5 | /usr/local/bin/timestamp.sh