问题
I have seen echo being used like this in many places:
echo >&2 message text ...
What does this mean?
I understand 2>&1, however, I am not sure how to interpret the usage above.
Can anyone please explain?
回答1:
To quickly explain what the others missed:
echo "hey" >&2
> redirect standard output (implicit 1>)
& what comes next is a file descriptor, not a file (only for right hand side of >)
2 stderr file descriptor number
Redirect stdout from echo command to stderr. (If you were to useecho "hey" >2 you would output hey to a file called 2)
回答2:
The use of >&2 here is sending the output to standard error instead of standard out. This is generally the better place to send logging output that isn't the actual result of the computation, especially if the result is printed to standard out (possibly redirected to a file) rather than to some other file output (i.e. sending the logging to standard error ensures that it won't get included with the real output that was redirected to the output file).
回答3:
The >&2 redirection is a shortcut for 1>& 2.
You understand 2>& 1 so you will understand that this links the command's stdout to the current stderr
回答4:
While other answers give good explanations, they're missing the exact question that is being asked here. The best answer is in the form of a comment directly on the question, but alas, Stack Overflow does not consider me worthy of being allowed to add comments.
So, quoting tripleee:
The previse [sic] position of the redirection in the command line is not important. All of
>&2 echo messageandecho >&2 messageandecho message >&2are equivalent.
This is the exact question that I came looking for, and none of the current answers answer that; they just explain things that I already knew. On the other hand, the question could benefit from better phrasing, but again, I am barred from commenting, so...
来源：https://stackoverflow.com/questions/23489934/echo-2-some-text-what-does-it-mean-in-shell-scripting