检查从命令的输出零线通过SSH [英] Check for zero lines output from command over SSH

问题描述

如果我这样做，而网络出现故障，那么零的情况下将被执行，它不应该的。

If I do the following, and the network is down, then the zero case will be executed, which it shouldn't.

case "$(ssh -n $host zfs list -t snapshot -o name -H | grep "tank/fs" | wc -l | awk '{print $1}')" in
    0)  # do something
        ;;
    1)  # do something else
        ;;
    *)  # fail
esac

在我检查，我可以SSH到 $主机脚本较早，但今天我发现了这个问题，去哪儿网我的支票后立即失败。

Earlier in the script I check that I can SSH to $host, but today I found this problem, where the network failed right after my check.

如果我检查从SSH命令的返回值，那么我将永远，因为它是最后执行获得 AWK 的返回值。

If I check the return value from the SSH command, then I will always get the return value from awk as it is executed last.

问

我如何确保我其实算零线的 ZFS 输出，并从失败的SSH连接没有零线？

How do I insure that I actually count zero lines that zfs outputted, and not zero lines from a failed SSH connection?

推荐答案

说：

set -o pipefail

在你的脚本的开头（或案前语句）。

此外，执行案前检查命令的返回code 语句：

set -o pipefail
$value=$(ssh -n $host zfs list -t snapshot -o name -H | grep "tank/fs" | wc -l | awk '{print $1}')
if [ $? == 0 ]; then
   case $value in
     ...
   esac
fi

从手动：

pipefail

如果设置，管道的返回值是最后的值
  （最右边）的命令与非零状态退出，或零如果所有
  在成功地管道出口命令。此选项被禁用
  默认值。

If set, the return value of a pipeline is the value of the last (rightmost) command to exit with a non-zero status, or zero if all commands in the pipeline exit successfully. This option is disabled by default.

这篇关于检查从命令的输出零线通过SSH的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！