循环只在主体中使用 `ssh` 迭代一次 [英] Loop only iterates once with `ssh` in the body

问题描述

我经常看到与...基本相同的问题

I often see questions which are essentially the same as...

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当我在循环体中调用 ssh 时，我的 while 循环只迭代一次.

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My while loop only iterates once when I call ssh in the body of the loop.

while read -r line; do
    ssh somehost "command $line"
done < argument_list.txt

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推荐答案

ssh 也从标准输入读取，所以第一次调用 ssh 消耗了剩余的 >argument_list.txt 在下一次调用 read 之前.要解决此问题，请使用

ssh also reads from standard input, so the first call to ssh consumes the rest of argument_list.txt before the next call to read. To fix, either redirect ssh's standard input from /dev/null using either

ssh somehost "command $line" < /dev/stdin

或

ssh -n somehost "command $line"

如果 ssh 确实确实需要从标准输入中读取，您不希望它从 argument_list.txt.在这种情况下，您需要为 while 循环使用不同的文件描述符.

In the event that ssh really does need to read from standard input, you don't want it reading more data from argument_list.txt. In this case, you need to use a different file descriptor for the while loop.

while read -r line <&3; do
    ssh somehost "command $line"
done 3< argument_list.txt

bash 和其他一些 shell 也允许 read 使用 -u 选项来指定文件描述符，有些人可能会发现它更具可读性.

bash and some other shells also allow read to take a -u option to specify the file descriptor, which some might find more readable.

while read -r -u 3 line; do
    ssh somehost "command $line"
done 3< argument_list.txt

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