bash “模糊输出重定向”试图从发送到 at 的命令将 stdout 和 stderr 发送到 mailx
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"Ambiguous output redirect" trying to send both stdout and stderr to mailx from a command sent to at
提问by tomocafe
I have a bash script called test.shwhich, for the sake of simplicity, prints one line to stdoutand one line to stderr.
我有一个名为test.sh的 bash 脚本，为了简单起见，它向stdout打印一行，向stderr打印一行。
test.sh:
测试.sh：
#!/bin/bash
echo "this is to stdout"
echo "this is to stderr" 1>&2
I want to run the script test.shat 7:00 PM, but only if certain conditions are met. To this end, I have another bash script called schedule.sh, which checks some stuff and then submits the command to atto be run later.
我想在晚上 7:00运行脚本test.sh，但前提是满足某些条件。为此，我有另一个名为schedule.sh 的bash 脚本，它会检查一些东西，然后提交at要稍后运行的命令。
I want the output of test.sh(both stdoutand stderr) to be sent to me in an email. I use mailxto do this so I can get a nice subject name.
我希望test.sh的输出（包括stdout和stderr）通过电子邮件发送给我。我过去mailx常常这样做，所以我可以获得一个很好的主题名称。
Furthermore, I want atto shut up. No output from atbecause it always sends me ugly emails (no subject line) if atproduces any output.
而且，我想at闭嘴。没有输出，at因为如果at产生任何输出，它总是向我发送丑陋的电子邮件（没有主题行）。
schedule.sh:
时间表.sh：
#!/bin/bash
my_email="[email protected]" # Email is a variable
# Check some stuff, exit if certain conditions not met
echo "~/test.sh 2>&1 | mailx -s\"Cool title\" $my_email" | at 7:00 PM &> /dev/null
What's interesting is that when I run schedule.shfrom cron(which runs the script with sh), it works perfectly. However, when I manually run schedule.shfrom the terminal (NB: I'm using tcsh), at(not mailx) sends me an email saying
有趣的是，当我从（用 运行脚本）运行schedule.sh时，它运行良好。但是，当我从终端手动运行schedule.sh 时（注意：我正在使用），（不是）给我发送一封电子邮件说cronshtcshatmailx
Ambiguous output redirect.
I'm not sure why the shell I run schedule.shfrom makes a difference, when schedule.shis a bash script.
当schedule.sh是一个 bash 脚本时，我不确定为什么我运行schedule.sh的 shell会有所不同。
Here is my thinking in looking at schedule.sh. Everything within the quotation marks "~/test.sh 2>&1 | mailx -s\"Cool title\" [email protected]"should be an argument to at, and atruns that argument as a command using sh. The redirection 2>&1 |is in the style of shfor this reason.
这是我在查看schedule.sh 时的想法。引号内的所有内容都"~/test.sh 2>&1 | mailx -s\"Cool title\" [email protected]"应该是 的参数at，并at使用 将该参数作为命令运行sh。出于这个原因，重定向2>&1 |的风格是sh。
When I remove 2>&1and only pipe the stdoutof test.shto mailx, it does work; however, I receive 2 emails: one with stdoutfrom mailxand another from stderrfrom at.
当我删除2>&1并仅将test.sh的标准输出通过管道传输到 时，它确实有效；不过，我收到2封电子邮件：一个标准输出从另一个来自标准错误的。mailxmailxat
What gives? How can I make this work regardless of the shell I'm calling it from?
是什么赋予了？无论我从哪个 shell 调用它，我怎样才能使它工作？
Thanks.
谢谢。
edit:
编辑：
uname -osays my OS is GNU/Linux
uname -o说我的操作系统是 GNU/Linux
Here is uname -aif it helps:
这是uname -a它是否有帮助：
Linux [hostname censored] 2.6.9-89.ELlargesmp #1 SMP Mon Jun 22 12:46:58 EDT 2009 x86_64 x86_64 x86_64 GNU/Linux
When I check the atcontents using at -c, here's what I see:
当我at使用 来检查内容时at -c，我看到的是：
#!/bin/sh
# atrun uid=xxxxx gid=xxxxx
# mail username 0
# ...
SHELL=/bin/tcsh; export SHELL
# ...
${SHELL:-/bin/sh} << `(dd if=/dev/urandom count=200 bs=1 2>/dev/null|LC_ALL=C tr -d -c '[:alnum:]')`
~/test.sh 2>&1 | mailx -s"Cool title" [email protected]
I'm having a hard time understanding the second to last line... is this going to execute using $SHELL or /bin/sh?
我很难理解倒数第二行...这是要使用 $SHELL 还是执行/bin/sh？
采纳答案by Keith Thompson
The command executed via atis:
通过执行的命令at是：
~/test.sh 2>&1 | mailx -s\"Cool title\" $my_email
The behavior of atcommand varies from one system to another. On Linux, the command is executed using /bin/sh. In fact, on my system (Linux Mint 14), it prints a warning message:
at命令的行为因系统而异。在 Linux 上，该命令使用/bin/sh. 事实上，在我的系统（Linux Mint 14）上，它会打印一条警告消息：
$ echo 'printenv > at.env' | at 19:24
warning: commands will be executed using /bin/sh
On Solaris, the command is executed by the shell specified by the current value of the $SHELLenvironment variable. Using an account where my default shell is /bin/tcshon Solaris 9, I get:
在 Solaris 上，命令由$SHELL环境变量的当前值指定的 shell 执行。使用我的默认 shell/bin/tcsh在 Solaris 9 上的帐户，我得到：
% echo 'printenv > at.env' | at 19:25
commands will be executed using /bin/tcsh
job 1397874300.a at Fri Apr 18 19:25:00 2014
% echo 'printenv > at.env' | env SHELL=/bin/sh at 19:28
commands will be executed using /bin/sh
job 1397874480.a at Fri Apr 18 19:28:00 2014
Given that at's behavior is inconsistent (and frankly confusing), I suggest having it execute just a single command, with any I/O redirection being performed inside that command. That's the best way to ensure that the command will be executed correctly regardless of which shell is used to execute it.
鉴于该at的行为不一致（坦率地说令人困惑），我建议让它只执行一个命令，在该命令内执行任何 I/O 重定向。这是确保无论使用哪个 shell 执行命令都能正确执行命令的最佳方法。
For example (untested code follows):
例如（未经测试的代码如下）：
echo '#!/bin/bash' > tmp.bash
echo "~/test.sh 2>&1 | mailx -s\"Cool title\" $my_email" >> tmp.bash
chmod +x tmp.bash
echo "./tmp.bash" | at 7:00 PM
