可变$ x $ n算术扩展
我遇到了这个教程示例，尤其是行sum = $ = $（（$ sum+$ x $ n））。 $ x $ n特别是什么意思？我想引用$ x但未分配（未宣布/未设置变量），不是吗？
https://linuxhint.com/bash_eval_command/
#!/bin/bash
# Initialize the variable $sum with the value 0
sum=0
# Declare a for loop that will iterate for 4 times
for n in {1..4}
do
# Create four variables using eval command
eval x$n=$n
# Add the values of the variable with $sum
sum=$(($sum+$x$n))
done
# Assign `echo` command with string into a variable
command="echo 'The result of the sum='"
# `eval` command print the sum value using variables
eval $command $sum
I come across this tutorial example, especial the line sum=$(($sum+$x$n)). What does $x$n mean in particular? I suppose $x is referenced but not assigned (undeclared/unset variable), isn't it?
https://linuxhint.com/bash_eval_command/
evaltest3.sh
#!/bin/bash
# Initialize the variable $sum with the value 0
sum=0
# Declare a for loop that will iterate for 4 times
for n in {1..4}
do
# Create four variables using eval command
eval x$n=$n
# Add the values of the variable with $sum
sum=$(($sum+$x$n))
done
# Assign `echo` command with string into a variable
command="echo 'The result of the sum='"
# `eval` command print the sum value using variables
eval $command $sum
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（不是直接回答您的问题，而是提供替代方案）
，因为Bash Arithmetic允许我们提供变量“不使用参数扩展语法” [ ref ]（即没有
$），我们可以写出优势是bash bash and bash and bash and bash and bash and bash andley and bash and bash andlen offeres数量零。
(Does not directly answer your question, but offers an alternative)
Since bash arithmetic allows us to provide variables "without using the parameter expansion syntax" [Ref] (i.e. without the
$), we can writeThe advantage is that bash handles empty or unset variables as the number zero.