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, Jun 06 '14 at 21:07

user unknown · Answer 1 · 2014-06-06T21:00:37.120

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 06 '14 at 21:00

answered Mar 19 '12 at 10:09

user unknown

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How do you know if the output is written to stderr or stdout? – user1527227 Jul 25 '14 at 19:59
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@user1527227: You can test it. – user unknown Jul 26 '14 at 08:41
A bit late but Thank you!! – Murad Alm. Dec 19 '19 at 23:35

score 16 · Answer 2 · edited Mar 19 '12 at 10:21

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 '12 at 10:21

bmk

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answered Mar 19 '12 at 10:15

Eran Ben-Natan

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thank you for your insight, it seems top also prints the version too stderr – user1278282 Mar 19 '12 at 12:31

Bash script store command output into variable

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