bash 如何在 if 块的变量中捕获命令错误消息
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how to capture command error message in variable for if block
提问by agarwal_achhnera
Hi below is my code for bash shell script, in this I want to capture error message for if clause, when it says either job is already running or unable to start the job to a variable, how it is possible in below script, or any other way for the below functionality
嗨，下面是我的 bash shell 脚本代码，在此我想捕获 if 子句的错误消息，当它说作业已经在运行或无法启动变量的作业时，在下面的脚本中如何可能，或任何以下功能的其他方式
if initctl start $i ; then
echo "service $i started by script"
else
echo "not able to start service $i"
fi
回答by fedorqui 'SO stop harming'
You can for example use the syntax msg=$(command 2>&1 1>/dev/null)to redirect stderr to stdout after redirecting stdout to /dev/null. This way, it will just store stderr:
例如，您可以msg=$(command 2>&1 1>/dev/null)在将 stdout 重定向到 /dev/null 之后使用语法将 stderr 重定向到 stdout。这样，它只会存储 stderr：
error=$(initctl start $i 2>&1 1>/dev/null)
if [ $? -eq 0 ]; then
echo "service $i started by script"
else
echo "service $i could not be started. Error: $error"
fi
This uses How to pipe stderr, and not stdout?, so that it catches stderr from initctl start $iand stores in $errorvariable.
这使用如何管道 stderr，而不是 stdout？，以便它从变量中捕获 stderrinitctl start $i并存储在$error变量中。
Then, $?contains the return code of the command, as seen in How to check if a command succeeded?. If 0, it succeeded; otherwise, some errors happened.
然后，$?包含命令的返回码，如如何检查命令是否成功？. 如果0，则成功；否则，会发生一些错误。
回答by rurouni88
Use '$?' variable It stores any exit_code from the previous statement See http://www.tldp.org/LDP/abs/html/exitcodes.htmlfor more information
使用“$?” 变量 它存储上一条语句中的任何 exit_code 请参阅http://www.tldp.org/LDP/abs/html/exitcodes.html了解更多信息
initctl start $i
retval=$?
if [ $retval -eq 0 ]; then
echo "service $i started by script"
else
echo "not able to start service $i"
fi
