bash 检查在 while 循环中调用的程序的退出代码
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Check exit code of a program called in a while loop
提问by Micha? Trybus
I would like to write a loop in bash which executes until a certain command stops failing (returning non-zero exit code), like so:
我想在 bash 中编写一个循环，该循环会一直执行，直到某个命令停止失败（返回非零退出代码），如下所示：
while ! my_command; do
# do something
done
But inside this loop I need to check which exit code my_commandreturned, so I tried this:
但是在这个循环中，我需要检查my_command返回的是哪个退出代码，所以我尝试了这个：
while ! my_command; do
if [ $? -eq 5 ]; then
echo "Error was 5"
else
echo "Error was not 5"
fi
# potentially, other code follows...
done
But then the special variable ?becomes 0inside the loop body.
The obvious solution is:
但随后特殊变量?就变成0了循环体内部。显而易见的解决方案是：
while true; do
my_command
EC=$?
if [ $EC -eq 0 ]; then
break
fi
some_code_dependent_on_exit_code $EC
done
How can I check the exit code of my_command(called in loop header) inside loop body without rewriting this example using a while trueloop with a break condition as shown above?
如何my_command在不使用while true具有中断条件的循环重写此示例的情况下检查循环体内部（在循环头中调用）的退出代码，如上所示？
回答by chepner
In addition to the well-known whileloop, POSIX provides an untilloop that eliminates the need to negate the exit status of my_command.
除了众所周知的while循环之外，POSIX 还提供了一个until循环，无需否定 的退出状态my_command。
# To demonstrate
my_command () { read number; return $number; }
until my_command; do
if [ $? -eq 5 ]; then
echo "Error was 5"
else
echo "Error was not 5"
fi
# potentially, other code follows...
done
回答by F. Hauri
If truecommand hurt your sensibility, you could write:
如果true命令伤害了你的敏感性，你可以写：
while my_command ; ret=$? ; [ $ret -ne 0 ];do
echo do something with $ret
done
This could be simplified:
这可以简化：
while my_command ; ((ret=$?)) ;do
echo do something with $ret
done
But if you don't need ResultCode, you could simply:
但如果您不需要ResultCode，您可以简单地：
while my_command ; [ $? -ne 0 ];do
echo Loop on my_command
done
or
或者
while my_command ; (($?)) ;do
echo Loop on my_command
done
But from there you could better use untilas chepner suggest
但从那里你可以更好地使用untilchepner 建议
回答by pjh
You can get the status of a negated command from the PIPESTATUSbuilt-in variable:
您可以从PIPESTATUS内置变量中获取否定命令的状态：
while ! my_command ; do
some_code_dependent_on_exit_code "${PIPESTATUS[0]}"
done
chepner's solution is better in this case, but PIPESTATUSis sometimes useful for similar problems.
在这种情况下，chepner 的解决方案更好，但PIPESTATUS有时对类似问题很有用。
