echo >&2 "some text" what does it mean in shell scripting
ShellUnixShShell Problem Overview
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?
Shell Solutions
Solution 1 - Shell
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
)
Solution 2 - Shell
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).
Solution 3 - Shell
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 message
and
> echo >&2 message
and echo message >&2
are 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...
Solution 4 - Shell
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
Solution 5 - Shell
command > /yourfile is equal to command 1 > /yourfile
so >&2 is same as 1 > &2 redirect stdout to stderr