在backticked命令的bash PIPESTATUS？ [英] bash pipestatus in backticked command?

问题描述

在bash，如果我执行了几个命令的反引号里面的管道连接到一起，我怎么能找到的第一个命令的退出状态？

in bash, if I execute a couple of commands piped together inside of backticks, how can I find out the exit status of the first command?

即。在这种情况下，我想获得的1。我可以，如果我不使用反引号，但似乎不工作时，我想保存输出通过PIPESTATUS [0]得到：

i.e. in this case, I am trying to get the "1". which I can get via PIPESTATUS[0] if I am not using backticks, but which doesn't seem to work when I want to saving the output:

## PIPESTATUS[0] works to give me the exit status of 'false':
$ false | true;
$ echo $? ${PIPESTATUS[0]} ${PIPESTATUS[1]};
0 1 0

## doesn't work:
$ a=`false | true`;
$ echo $? ${PIPESTATUS[0]} ${PIPESTATUS[1]};
0 0

更一般地，我试图做到：节省一些程序的输出给一个变量的最后一行，但能够告诉我们，如果计划失败：

More generally, I am trying to accomplish: save the last line of the output of some program to a variable, but be able to tell if the program failed:

$ myvar=` ./someprogram | tail -1 `;
$ if [ "what do i put here" ]; then echo "program failed!"; fi

理想我也想明白是怎么回事，得到的答复是没有什么。

Ideally I'd also like to understand what is going on, not just what the answer is.

感谢。

推荐答案

尝试设置 pipefail 选项。它返回失败管道的最后一个命令。一个例子是：

Try to set pipefail option. It returns the last command of the pipeline that failed. One example:

首先，我将其禁用：

set +o pipefail

创建一个 perl的脚本（ script.pl ）来测试管道：

#!/usr/bin/env perl

use warnings;
use strict;

if ( @ARGV ) { 
    die "Line1\nLine2\nLine3\n";
}
else {
    print "Line1\nLine2\nLine3\n";
}

在命令行中运行：

myvar=`perl script.pl | tail -1`
echo $? "$myvar"

这收益率：

0 Line3

这似乎是正确的，让我们看到 pipefail 已启用：

set -o pipefail

和运行命令：

myvar=`perl script.pl fail 2>&1 | tail -1`
echo $? "$myvar"

这收益率：

255 Line3

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