HOSTNAME environment variable on Linux












17















On my Linux box (Gentoo Linux 2.6.31 to be specific) I have noticed that the HOSTNAME environment variable is available in my shell, but not in scripts. For example,



$ echo $HOSTNAME


returns



xxxxxxxx.com,


but



$ ruby -e 'puts ENV["HOSTNAME"]'


returns



nil


On the other hand, the USER environment variable, for instance, is available both in the shell and in scripts.



I have noticed that USER appears in the list of environment variables that appears when I type



export


i.e.,



declare -x USER="infogrind"


but HOSTNAME doesn't. I suspect the issue has something to do with that.



My questions: 1) how can I make HOSTNAME available in scripts, and 2) for my better understanding, where is this variable initially set, and why is it not "exported"?










share|improve this question



























    17















    On my Linux box (Gentoo Linux 2.6.31 to be specific) I have noticed that the HOSTNAME environment variable is available in my shell, but not in scripts. For example,



    $ echo $HOSTNAME


    returns



    xxxxxxxx.com,


    but



    $ ruby -e 'puts ENV["HOSTNAME"]'


    returns



    nil


    On the other hand, the USER environment variable, for instance, is available both in the shell and in scripts.



    I have noticed that USER appears in the list of environment variables that appears when I type



    export


    i.e.,



    declare -x USER="infogrind"


    but HOSTNAME doesn't. I suspect the issue has something to do with that.



    My questions: 1) how can I make HOSTNAME available in scripts, and 2) for my better understanding, where is this variable initially set, and why is it not "exported"?










    share|improve this question

























      17












      17








      17








      On my Linux box (Gentoo Linux 2.6.31 to be specific) I have noticed that the HOSTNAME environment variable is available in my shell, but not in scripts. For example,



      $ echo $HOSTNAME


      returns



      xxxxxxxx.com,


      but



      $ ruby -e 'puts ENV["HOSTNAME"]'


      returns



      nil


      On the other hand, the USER environment variable, for instance, is available both in the shell and in scripts.



      I have noticed that USER appears in the list of environment variables that appears when I type



      export


      i.e.,



      declare -x USER="infogrind"


      but HOSTNAME doesn't. I suspect the issue has something to do with that.



      My questions: 1) how can I make HOSTNAME available in scripts, and 2) for my better understanding, where is this variable initially set, and why is it not "exported"?










      share|improve this question














      On my Linux box (Gentoo Linux 2.6.31 to be specific) I have noticed that the HOSTNAME environment variable is available in my shell, but not in scripts. For example,



      $ echo $HOSTNAME


      returns



      xxxxxxxx.com,


      but



      $ ruby -e 'puts ENV["HOSTNAME"]'


      returns



      nil


      On the other hand, the USER environment variable, for instance, is available both in the shell and in scripts.



      I have noticed that USER appears in the list of environment variables that appears when I type



      export


      i.e.,



      declare -x USER="infogrind"


      but HOSTNAME doesn't. I suspect the issue has something to do with that.



      My questions: 1) how can I make HOSTNAME available in scripts, and 2) for my better understanding, where is this variable initially set, and why is it not "exported"?







      linux shell environment-variables






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked Apr 19 '10 at 8:16







      user34614





























          1 Answer
          1






          active

          oldest

          votes


















          16














          $HOSTNAME is a Bash variable that's set automatically (rather than in a startup file). Ruby probably runs sh for its shell and it doesn't include that variable. There's no reason you can't export it yourself.



          bash$ echo $HOSTNAME
          foobar
          bash$ sh -c 'echo $HOSTNAME'

          bash$ export HOSTNAME
          bash$ sh -c 'echo $HOSTNAME'
          foobar


          You could add the export command to one of your startup files, such as ~/.bashrc.



          In Ruby (irb shown):



          >> require 'socket'
          => true
          >> Socket.gethostname
          => "bazinga"





          share|improve this answer





















          • 2





            It is usually better to use gethostname() because of this.

            – grawity
            Apr 19 '10 at 11:25








          • 2





            The posix standard enumerates the environment variables you should expect on a posix-compliant systems, and HOSTNAME is not in the list: pubs.opengroup.org/onlinepubs/009695399/basedefs/…

            – qneill
            Apr 22 '15 at 20:56













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          1 Answer
          1






          active

          oldest

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          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          16














          $HOSTNAME is a Bash variable that's set automatically (rather than in a startup file). Ruby probably runs sh for its shell and it doesn't include that variable. There's no reason you can't export it yourself.



          bash$ echo $HOSTNAME
          foobar
          bash$ sh -c 'echo $HOSTNAME'

          bash$ export HOSTNAME
          bash$ sh -c 'echo $HOSTNAME'
          foobar


          You could add the export command to one of your startup files, such as ~/.bashrc.



          In Ruby (irb shown):



          >> require 'socket'
          => true
          >> Socket.gethostname
          => "bazinga"





          share|improve this answer





















          • 2





            It is usually better to use gethostname() because of this.

            – grawity
            Apr 19 '10 at 11:25








          • 2





            The posix standard enumerates the environment variables you should expect on a posix-compliant systems, and HOSTNAME is not in the list: pubs.opengroup.org/onlinepubs/009695399/basedefs/…

            – qneill
            Apr 22 '15 at 20:56


















          16














          $HOSTNAME is a Bash variable that's set automatically (rather than in a startup file). Ruby probably runs sh for its shell and it doesn't include that variable. There's no reason you can't export it yourself.



          bash$ echo $HOSTNAME
          foobar
          bash$ sh -c 'echo $HOSTNAME'

          bash$ export HOSTNAME
          bash$ sh -c 'echo $HOSTNAME'
          foobar


          You could add the export command to one of your startup files, such as ~/.bashrc.



          In Ruby (irb shown):



          >> require 'socket'
          => true
          >> Socket.gethostname
          => "bazinga"





          share|improve this answer





















          • 2





            It is usually better to use gethostname() because of this.

            – grawity
            Apr 19 '10 at 11:25








          • 2





            The posix standard enumerates the environment variables you should expect on a posix-compliant systems, and HOSTNAME is not in the list: pubs.opengroup.org/onlinepubs/009695399/basedefs/…

            – qneill
            Apr 22 '15 at 20:56
















          16












          16








          16







          $HOSTNAME is a Bash variable that's set automatically (rather than in a startup file). Ruby probably runs sh for its shell and it doesn't include that variable. There's no reason you can't export it yourself.



          bash$ echo $HOSTNAME
          foobar
          bash$ sh -c 'echo $HOSTNAME'

          bash$ export HOSTNAME
          bash$ sh -c 'echo $HOSTNAME'
          foobar


          You could add the export command to one of your startup files, such as ~/.bashrc.



          In Ruby (irb shown):



          >> require 'socket'
          => true
          >> Socket.gethostname
          => "bazinga"





          share|improve this answer















          $HOSTNAME is a Bash variable that's set automatically (rather than in a startup file). Ruby probably runs sh for its shell and it doesn't include that variable. There's no reason you can't export it yourself.



          bash$ echo $HOSTNAME
          foobar
          bash$ sh -c 'echo $HOSTNAME'

          bash$ export HOSTNAME
          bash$ sh -c 'echo $HOSTNAME'
          foobar


          You could add the export command to one of your startup files, such as ~/.bashrc.



          In Ruby (irb shown):



          >> require 'socket'
          => true
          >> Socket.gethostname
          => "bazinga"






          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited Jan 11 at 1:13

























          answered Apr 19 '10 at 9:50









          Dennis WilliamsonDennis Williamson

          76.6k14129167




          76.6k14129167








          • 2





            It is usually better to use gethostname() because of this.

            – grawity
            Apr 19 '10 at 11:25








          • 2





            The posix standard enumerates the environment variables you should expect on a posix-compliant systems, and HOSTNAME is not in the list: pubs.opengroup.org/onlinepubs/009695399/basedefs/…

            – qneill
            Apr 22 '15 at 20:56
















          • 2





            It is usually better to use gethostname() because of this.

            – grawity
            Apr 19 '10 at 11:25








          • 2





            The posix standard enumerates the environment variables you should expect on a posix-compliant systems, and HOSTNAME is not in the list: pubs.opengroup.org/onlinepubs/009695399/basedefs/…

            – qneill
            Apr 22 '15 at 20:56










          2




          2





          It is usually better to use gethostname() because of this.

          – grawity
          Apr 19 '10 at 11:25







          It is usually better to use gethostname() because of this.

          – grawity
          Apr 19 '10 at 11:25






          2




          2





          The posix standard enumerates the environment variables you should expect on a posix-compliant systems, and HOSTNAME is not in the list: pubs.opengroup.org/onlinepubs/009695399/basedefs/…

          – qneill
          Apr 22 '15 at 20:56







          The posix standard enumerates the environment variables you should expect on a posix-compliant systems, and HOSTNAME is not in the list: pubs.opengroup.org/onlinepubs/009695399/basedefs/…

          – qneill
          Apr 22 '15 at 20:56




















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