Bash script store command output into variable

Question

I have a problem concerning storing the output of a command inside a variable within a bash script.
I know in general there are two ways to do this

either

foo=$(bar)
# or
foo=`bar`

but for the Java version query, this doesn't seem to work.

I did:

version=$(java --version)

This doesn't store the value inside the var. It even still prints it, which really shouldn't be the case.

I also tried redirecting output to a file but this also fails.

there are more than two ways. read foo < <( echo "this is another way") but this is unrelated to your problem with catching error output, answered below already. — Deleted User
– Deleted User, Commented Jun 6, 2014 at 21:07

user unknown · Accepted Answer · 2014-06-06 21:00:37Z

72

 version=$(java -version 2>&1)

The version param only takes one dash, and if you redirect stderr, which is, where the message is written to, you'll get the desired result.

As a sidenote, using two dashes is an inofficial standard on Unix like systems, but since Java tries to be almost identical over different platforms, it violates the Unix/Linux-expectations and behaves the same in this regard as on windows, and as I suspect, on Mac OS.

edited Jun 6, 2014 at 21:00

answered Mar 19, 2012 at 10:09

user unknown

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3 Comments

user1527227 Over a year ago

How do you know if the output is written to stderr or stdout?

user unknown Over a year ago

@user1527227: You can test it.

Murad Alm. Over a year ago

A bit late but Thank you!!

bmk · Accepted Answer · 2012-03-19 10:21:19Z

16

That is because java -version writes to stderr and not stdout. You should use:

version=$(java -version 2>&1)

In order to redirect stderr to stdout.

You can see it by running the following 2 commands:

java -version > /dev/null

java -version 2> /dev/null

edited Mar 19, 2012 at 10:21

bmk

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answered Mar 19, 2012 at 10:15

Eran Ben-Natan

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1 Comment

user1278282 Over a year ago

thank you for your insight, it seems top also prints the version too stderr

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