在bash for循环中评估表达式 [英] Evaluate expression inside bash for loop

问题描述

如果执行此操作，将得到预期的结果.

If I do this, I get the result as expected.

for i in {125..129}; do echo $i; done
125
126
127
128
129

但是，当我这样做时?我有点奇怪.

But when I do this? I get something weired.

for i in {$((1+(25-1)*500))..$((25*500))}; do echo $i; done

{12001..12500}

我希望在循环变量中传递一个变量，例如 $((1 +($ j-1)* 500))

I wish to pass a variable inside the loop variables like $((1+($j-1)*500))

推荐答案

Bash的括号扩展有局限性.您想要的是 seq :

Bash's brace expansion has limitations. What you want is seq:

for i in $( seq $((1+(25-1)*500)) $((25*500)) ); do echo $i; done

以上内容将循环显示从12001年到12500年的所有数字.

The above will loop over all numbers from 12001 to 12500.

seq 类似于bash的花括号:

seq is similar to bash's braces:

$ echo {2..4}
2 3 4
$ echo $(seq 2 4)
2 3 4

seq 的主要优点是它的参数不仅可以包括如上所示的算术表达式，还可以包括shell变量:

The key advantage of seq is that its arguments can include not just arithmetic expressions, as shown above, but also shell variables:

$ x=4; echo $(seq $((x-2)) $x)
2 3 4

通过对比，大括号符号将不接受.

By contrast, the brace notation will accept neither.

seq 是GNU实用程序，可在所有linux系统以及OSX的最新版本中使用.较旧的BSD系统可以使用名为 jot 的类似实用程序.

seq is a GNU utility and is available on all linux systems as well as recent versions of OSX. Older BSD systems can use a similar utility called jot.

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