如何使用变量在for循环一个bash [英] How to use variables in a bash for loop

问题描述

一个人如何在for循环是bash使用一个变量？
如果我只是用循环标准，它做什么，我希望

How does one use a variable in a bash for loop? If I just use a standard for loop, it does what I expect

for i in {0..3}
do
   echo "do some stuff $i"
done

这工作正常。它循环直通4次，0至3包容性，打印我的消息，并把数结尾。

This works fine. It loops thru 4 times, 0 to 3 inclusive, printing my message and putting the count at the end.

do some stuff 0
do some stuff 1
do some stuff 2
do some stuff 3

当我尝试使用以下for循环，同样的事情，似乎等于一个字符串，这是不是我想要的。

When I try the same thing with the following for loop, it seems to equal a string, which is not what i want.

length=3
for i in {0..$length}
do
   echo "do something right $i"
done

输出：

do something right {0..3}

我试过

for i in {0.."$length"} and for i in {0..${length}} (both output was {0..3})

和

for i in {0..'$length'} (output was {0..$length})

和他们都没有做什么，我需要。希望有人能帮助我。感谢您事先的任何bash的专家与循环帮助。

and they both don't do what I need. Hopefully someone can help me. Thanks in advance for any bash expert's help with for loops.

推荐答案

一种方法是使用评估：

for i in $( eval echo {0..$length} )
do
       echo "do something right $i"
done

的注意的，当你设置时会发生什么长度=; LS 或长度=; RM * （不要试图后者虽然）。

Note what happens when you set length=;ls or length=; rm * (don't try the latter though).

的安全的，使用 SEQ ：

for i in $( seq 0 $length )
do
       echo "do something right $i"
done

，也可以使用C风格的for循环，这也是安全的：

or you can use the c-style for loop, which is also safe:

for (( i = 0; i <= $length; i++ )) 
do 
       echo "do something right $i"
done

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