Linux Bash：让语句与赋值
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Bash: let statement vs assignment
提问by IDDQD
What is the difference between assigning to a variable like var=fooand using let like let var=foo? Or cases like var=${var}barand let var+=bar? What are the advantages and disadvantages of each approach?
分配给变量 likevar=foo和使用 let like之间有什么区别let var=foo？或者像var=${var}bar和这样的情况let var+=bar？每种方法的优缺点是什么？
采纳答案by Aleks-Daniel Jakimenko-A.
letdoes exactly what (( ))do, it is for arithmetic expressions. There is almost no differencebetween letand (( )).
let确实做什么(( ))，它用于算术表达式。目前几乎没有差别之间let和(( ))。
Your examples are invalid. var=${var}baris going to add word barto the varvariable (which is a string operation), let var+=baris not going to work, because it is not an arithmetic expression:
你的例子无效。var=${var}bar要将单词添加bar到var变量（这是一个字符串操作），let var+=bar是行不通的，因为它不是算术表达式：
$ var='5'; let var+=bar; echo "$var"
5
Actually, it IS an arithmetic expression, if only variable barwas set, otherwise baris treated as zero.
实际上，它是一个算术表达式，如果只bar设置了变量，否则bar视为零。
$ var='5'; bar=2; let var+=bar; echo "$var"
7
