CODEWITHSUNDEEP
shellunixsh
CuriousMind
CuriousMind

Reputation: 8903

echo >&2 "some text" what does it mean in shell scripting

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?

Upvotes: 87

Views: 68999

Answers (5)

Henk Langeveld
Henk Langeveld

Reputation: 8446

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

Footnote about shell redirection syntax...

This looks like

{numfd}[operator]{whitespace}[target]

with the {...} parts optional. The whitespace between operator and target is recommended for readability, but is not required. On the other hand, if you include the {numfd} in front of the operator, there can not be any whitespace between the two of them.

[operator] can be one of <, >, >> for file targets and <&, >& for file descriptor targets.

{numfd} defaults to 0 for <, 1 for > and >>.

[target] is a filename, unless operator ends in &. In that case, it is interpreted as a numeric file descriptor.

Upvotes: 11

focus zheng
focus zheng

Reputation: 380

command > /yourfile is equal to command 1> /yourfile

so >&2 is same as 1>& 2 redirect stdout to stderr

Upvotes: 1

Dave.Haku
Dave.Haku

Reputation: 381

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...

Upvotes: 23

Jite
Jite

Reputation: 4368

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)

Upvotes: 170

Michael Aaron Safyan
Michael Aaron Safyan

Reputation: 95499

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).

Upvotes: 33

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