bash : parse output of command and store into variable

Question

I have made a command witch return 'version:X' .

ie:

$>./mybox -v
$>version:2

I don't understand why this isn't working :

 $>VERSION=$( /home/mybox -v | sed 's/.*version:\([0-9]*\).*/\1/')
 $>echo $VERSION
 $>

if I write this, it is ok :

 $>VERSION=$( echo "version:2" | sed 's/.*version:\([0-9]*\).*/\1/')
 $>echo $VERSION
 $>2

Regards

Jeff Bowman · Accepted Answer · 2015-08-14 17:26:54Z

5

It's pretty common for version/error/debugging information to be sent to stderr, not stdout. When running the command from a terminal, both will be printed, but only stdout will make it through the pipe to sed.

echo output always goes to stdout by default, which is why you're not having trouble there.

If the above is correct, you'll just need to redirect stderr (file descriptor 2) to stdout (file descriptor 1) before passing it along:

VERSION=$( /home/mybox -v 2>&1 | sed 's/.*version:\([0-9]*\).*/\1/')
#                         ^^^^

answered Aug 14, 2015 at 17:26

Jeff Bowman

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2 Comments

Sleafar Over a year ago

Wouldn't "version:2" appear at the console in this case? It doesn't in the example in the question.

Jeff Bowman Over a year ago

@Sleafar Typically yes, unless it was ignored in copy-paste or an artifact of console line-overwriting. This could have been a comment, but it was getting long and I decided to go with the hunch instead.

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