Bash脚本中if语句未触发问题求助

Hey there! Let's troubleshoot why your if statement isn't working as expected. First, let's start with a common version of what your existing script might look like (since you mentioned you can already print even numbers in the target range):

#!/bin/bash

read -p "Enter start number: " start
read -p "Enter end number: " end

for (( num=start; num<=end; num++ ))
do
    # Check if number is even
    if (( num % 2 == 0 ))
    then
        echo "$num"
        # Your attempted 7-divisibility check likely lives here with syntax issues
    fi
done

Common Issues That Break Your If Statement #

Most often, the problem comes down to one of these syntax or logic missteps:

• Forgetting required spaces around operators when using [ ... ] (e.g., [num%7==0] instead of [ $num % 7 -eq 0 ])
• Using incorrect arithmetic comparison operators (like = instead of == in (( ... )))
• Placing the 7-divisibility check outside the even-number check (so it runs for all numbers, not just even ones)
• Not building the output string correctly before printing

Fixed Script with Working Conditional #

Here's a revised version that adds the "Chocolate" label to even numbers divisible by 7:

#!/bin/bash

read -p "Enter start number: " start
read -p "Enter end number: " end

for (( num=start; num<=end; num++ ))
do
    # First filter for even numbers
    if (( num % 2 == 0 ))
    then
        # Start with just the number as output
        output="$num"
        
        # Check if this even number is divisible by 7
        if (( num % 7 == 0 ))
        then
            # Append the label if condition is met
            output="$output: Chocolate"
        fi
        
        # Print the final output string
        echo "$output"
    fi
done

Key Fixes Explained #

• We use (( ... )) for arithmetic checks: This syntax is more intuitive for math operations in Bash and avoids the strict space requirements of [ ... ].
• We build the output incrementally: Starting with just the number, we only append "Chocolate" if the divisibility condition passes, then print once.
• The 7-divisibility check is nested inside the even-number check: This ensures we only evaluate it for numbers you already want to print.

Test Example #

If you input start=10 and end=20, the output will look like this:

10
12
14: Chocolate
16
18
20

内容的提问来源于stack exchange，提问作者Mohammed Wasim