请求编写Bash WHILE循环成绩分级判定脚本

Hey Justin! You're absolutely right that a while loop is the way to go here—your initial code was on the right track, but we need to adjust it to handle continuous user input instead of just command-line arguments. Here's a complete, working script that meets your requirements, plus some extra input validation to avoid errors:

#!/bin/bash

# Continuous loop to prompt for grades until user enters 999
while true; do
    # Prompt user for input directly
    read -p "Please enter a grade (enter 999 to quit): " gr

    # Check if user wants to exit the program
    if [ "$gr" -eq 999 ]; then
        echo "Exiting now. Goodbye!"
        break
    fi

    # Validate input is a numeric value (prevents script errors)
    if ! [[ "$gr" =~ ^[0-9]+$ ]]; then
        echo "Oops, that's not a valid number. Please enter a numeric grade."
        continue
    fi

    # Determine and output the corresponding grade letter
    if [ "$gr" -ge 90 ]; then
        echo "A"
    elif [ "$gr" -ge 80 ]; then
        echo "B"
    elif [ "$gr" -ge 70 ]; then
        echo "C"
    else
        echo "Failed"
    fi
done

Key Adjustments & Breakdown: #

• Infinite while true Loop: This keeps the script running until we explicitly break out of it (when the user enters 999).
• read -p for Direct Input: Replaces command-line argument handling with on-the-fly user prompts, so you don't need to pass grades when launching the script.
• Clean Exit Condition: The check for 999 triggers a break to exit the loop gracefully with a friendly message.
• Input Validation: The regex check [[ "$gr" =~ ^[0-9]+$ ]] ensures the user enters a valid number—no more weird errors from accidental letters or symbols!
• Grade Logic: Your original grading rules are fully implemented with clear if/elif/else blocks that cover all score ranges.

To use this script:

1. Save it as grade_checker.sh
2. Make it executable with chmod +x grade_checker.sh
3. Run it with ./grade_checker.sh

内容的提问来源于stack exchange，提问作者Justin Siev