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Date: Thu, 26 Feb 2009 17:18:55 +0300
Message-ID: <240e377b0902260618ndca8ae7re0fdaac3ece6d5ea@mail.gmail.com>
Subject: Re: Can anyone verify Hadoop FS shell command return codes?
From: Mikhail Yakshin <greycat.na.kor@gmail.com>
To: core-user@hadoop.apache.org
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On Mon, Feb 23, 2009 at 4:02 PM, S D wrote:
> I'm attempting to use Hadoop FS shell (http://hadoop
> .apache.org/core/docs/current/hdfs_shell.html) within a ruby script. My
> challenge is that I'm unable to get the function return value of the
> commands I'm invoking. As an example, I try to run get as follows
>
> hadoop fs -get /user/hadoop/testFile.txt .
>
> From the command line this generally works but I need to be able to verify
> that it is working during execution in my ruby script. The command should
> return 0 on success and -1 on error. Based on
>
> http://pasadenarb.com/2007/03/ruby-shell-commands.html
>
> I am using backticks to make the hadoop call and get the return value. Here
> is a dialogue within irb (Ruby's interactive shell) in which the command was
> not successful:
>
> irb(main):001:0> `hadoop dfs -get testFile.txt .`
> get: null
> => ""
>
> and a dialogue within irb in which the command was successful
>
> irb(main):010:0> `hadoop dfs -get testFile.txt .`
> => ""
>
> In both cases, neither a 0 nor a 1 appeared as a return value; indeed
> nothing was returned. Can anyone who is using the FS command shell return
> values within any scripting language (Ruby, PHP, Perl, ...) please confirm
> that it is working as expected or send an example snippet?

You seem to confuse captured output of stdout and exit status. Try
analyzing $?.exitstatus in Ruby:

irb(main):001:0> `true`
=> ""
irb(main):002:0> $?.exitstatus
=> 0
irb(main):003:0> `false`
=> ""
irb(main):004:0> $?.exitstatus
=> 1

-- 
WBR, Mikhail Yakshin