while循环读取文件结束prematurely [英] while loop to read file ends prematurely

问题描述

最终的目标是让我的bash脚本在多个服务器上执行命令。我几乎有它成立。我的SSH认证工作，但这个简单的while循环是我的命。当我执行while循环，读我的文件主机名称，它工作正常，当我运行一个

The eventual goal is to have my bash script execute a command on multiple servers. I almost have it set up. My SSH authentication is working, but this simple while loop is killing me. When I execute the while loop, reading my file for host names, it works fine when I run a

SSH $ HOST的uname -a

ssh $HOST "uname -a"

但是当我试图运行另一个ssh命令，

but when I attempt to run another ssh command,

SSH $ HOSToslevel -s

ssh $HOST "oslevel -s"

while循环提前结束！我不明白。 为什么会在阅读时做循环运行的第一个命令完全正常的，但不能当第二个被添加？

the while loop ends early! I can't figure it out. Why would the while read do loop run perfectly fine with the first command, but not when the second is added?

我有一个名为hosts.list一个简单的文本文件，它有4个主机名，每行一个。

I have a simple text file called hosts.list that has 4 hostnames, one per line.

    $ cat hosts.list
    pcced1bip04
    pcced1bit04
    pcced1bo02
    pcced1bo04

    $ cat getinfo.bash
    #!/bin/bash
    set -x
    while read HOST
      do
        echo $HOST
        ssh $HOST "uname -a"
        #ssh $HOST "oslevel -s"
        echo ""
      done  < hosts.list`

当它运行时，它工作正常。它通过文件，一行一行地获得的的uname -a的结果。所以，一切都很好，对不对？ （很抱歉，但我打开设置-x ）。

When it runs, it works fine. It goes through the file, line by line and gets the results of "uname -a". So everything is fine, right? (Sorry, but I turned on set -x).

    $ ./getinfo.bash
    + read HOST
    + echo pcced1bip04
    pcced1bip04
    + ssh pcced1bip04 'uname -a'
    AIX pcced1bip04 1 6 0001431BD400
    + echo ''

    + read HOST
    + echo pcced1bit04
    pcced1bit04
    + ssh pcced1bit04 'uname -a'
    AIX pcced1bit04 1 6 0001431BD400
    + echo ''

    + read HOST
    + echo pcced1bo02
    pcced1bo02
    + ssh pcced1bo02 'uname -a'
    AIX pcced1bo02 1 6 0009FE2AD400
    + echo ''

    + read HOST
    + echo pcced1bo04
    pcced1bo04
    + ssh pcced1bo04 'uname -a'
    AIX pcced1bo04 1 6 0009FE2AD400
    + echo ''

    + read HOST
    $

当我使行 [SSH $ HOSToslevel -s]时出现问题。当我这样做，剧本只读取文件的第一行，然后停止。 为什么不是去到其他行？

The problem occurs when I enable the line [ssh $HOST "oslevel -s"]. When I do, the script only reads the first line of the file, and then stops. Why won't it go onto the other lines?

    $ ./getinfo.bash
    + read HOST
    + echo pcced1bip04
    pcced1bip04
    + ssh pcced1bip04 'uname -a'
    AIX pcced1bip04 1 6 0001431BD400
    + ssh pcced1bip04 'oslevel -s'
    6100-06-02-1044
    + echo ''

    + read HOST
    $

如果我有我的剧本有问题，为什么会被工作只用在while循环[SSH $ HOST的uname -a] 完美的罚款？

If I had a problem with my script, why would it be working perfectly fine with just the [ssh $HOST "uname -a"] in the while loop?

推荐答案

如果您运行从标准输入读取命令（如 SSH ）在循环中，你需要确保之一：

If you run commands which read from stdin (such as ssh) inside a loop, you need to ensure that either:

• 您的循环没有遍历标准输入


• 您的指令有它的标准输入重定向：

...否则，该命令可以消耗输入打算用于循环，使其结束。

...otherwise, the command can consume input intended for the loop, causing it to end.

前者：

while read -u 5 -r hostname; do
  ssh "$hostname" ...
done 5<file

...其中，使用bash 4.1或更高版本，可以使用自动文件描述符分配改写成这样：

...which, using bash 4.1 or newer, can be rewritten with automatic file descriptor assignment as so:

while read -u "$file_fd" -r hostname; do
  ssh "$hostname" ...
done {file_fd}<file

后者：

while read -r hostname; do
  ssh "$hostname" ... </dev/null
done <file

...还可以，单独SSH，也可以用 -n 近似参数（也是从的/ dev /标准输入重定向空）

while read -r hostname; do
  ssh -n "$hostname"
done <file

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