Shell脚本技术问询：如何实现指定数值范围内的完全数检测与输出

Hey there! Nice work getting the single perfect number check up and running—let's expand that script to handle a range of numbers, including the until loop approach you're curious about.

First, let's refactor your existing check into a reusable function. This makes the code cleaner and easier to call as we iterate through the range:

# Function to check if a number is perfect
is_perfect() {
    local no=$1  # The number to check
    local i=1
    local ans=0
    local half=$((no / 2))  # Calculate half once for efficiency

    # Sum all divisors up to half the number
    while [ $i -le $half ]
    do
        if [ $((no % i)) -eq 0 ]
        then
            ans=$((ans + i))
        fi
        i=$((i + 1))
    done

    # Return true (0) if number equals sum of divisors, false (1) otherwise
    [ $no -eq $ans ]
}

Next, we'll add logic to get the range input from the user:

# Get range from user
echo "Enter the start of the range:"
read start
echo "Enter the end of the range:"
read end

Option 1: Using a for loop (intuitive for ranges) #

This is the most straightforward way to iterate through a range in bash:

echo -e "\nPerfect numbers between $start and $end (using for loop):"
for (( num=start; num<=end; num++ ))
do
    if is_perfect $num
    then
        echo $num
    fi
done

Option 2: Using an until loop (as you wanted to explore) #

The until loop runs until a condition becomes true. Here's how to use it to traverse the range:

echo -e "\nPerfect numbers between $start and $end (using until loop):"
num=$start  # Initialize counter to start of range

# Loop until num exceeds the end of the range
until [ $num -gt $end ]
do
    if is_perfect $num
    then
        echo $num
    fi
    num=$((num + 1))  # Increment counter
done

Quick notes on improvements: #

• I replaced expr with bash arithmetic expansion ($((...))) because it's faster and more readable—no need for subshells here.
• Using local variables in the function keeps them isolated from the rest of the script, preventing unexpected side effects.
• The is_perfect function returns an exit code (0 for true, 1 for false), which works seamlessly with bash's if statements.

Putting it all together, your full script would look like this:

#!/bin/bash

# Function to check if a number is perfect
is_perfect() {
    local no=$1
    local i=1
    local ans=0
    local half=$((no / 2))

    while [ $i -le $half ]
    do
        if [ $((no % i)) -eq 0 ]
        then
            ans=$((ans + i))
        fi
        i=$((i + 1))
    done

    [ $no -eq $ans ]
}

# Get range input
echo "Enter the start of the range:"
read start
echo "Enter the end of the range:"
read end

# Check with for loop
echo -e "\nPerfect numbers between $start and $end (for loop):"
for (( num=start; num<=end; num++ ))
do
    is_perfect $num && echo $num
done

# Check with until loop
echo -e "\nPerfect numbers between $start and $end (until loop):"
num=$start
until [ $num -gt $end ]
do
    is_perfect $num && echo $num
    num=$((num + 1))
done

Just save this as perfect_numbers.sh, make it executable with chmod +x perfect_numbers.sh, and run it—you'll be able to input a range and see all perfect numbers within it!

内容的提问来源于stack exchange，提问作者Diksha Nasa