Saving a < /dev/null result from remote host to local machine in text file












-1















I have the following code, which retrieves data from a remote host and display on local machine display.



if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then

ssh root@$192.168.80.180 'df -h; free -m' < /dev/null

echo /dev/null | cat - $var.txt

fi


How can I capture the result and save to a file, I tried echo but it didn't work.



Thank You






bash scripting







share|improve this question



























    -1















    I have the following code, which retrieves data from a remote host and display on local machine display.



    if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then
    
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null
    
echo /dev/null | cat - $var.txt
    
fi


    How can I capture the result and save to a file, I tried echo but it didn't work.



    Thank You






    bash scripting







    share|improve this question

























      -1












      -1








      -1








      I have the following code, which retrieves data from a remote host and display on local machine display.



      if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then
      
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null
      
echo /dev/null | cat - $var.txt
      
fi


      How can I capture the result and save to a file, I tried echo but it didn't work.



      Thank You






      bash scripting







      share|improve this question














      I have the following code, which retrieves data from a remote host and display on local machine display.



      if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then
      
ssh root@$192.168.80.180 'df -h; free -m' < /dev/null
      
echo /dev/null | cat - $var.txt
      
fi


      How can I capture the result and save to a file, I tried echo but it didn't work.



      Thank You






      bash scripting




      bash scripting






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked Nov 27 '18 at 20:58









      Huud RychHuud Rych

      65




      65
























          1 Answer
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          < /dev/null


          Binds the process standard output with /dev/null file.




          Saving a < /dev/null result ...




          /dev/null is a file and does not produce a result.




          ssh root@$192.168.80.180 'df -h; free -m' < /dev/null



          Runs ssh command with specified parameters and binds it's standard input with /dev/null.



          /dev/null is a magic file. It always has size equal to zero. You can write anything to it. It's size still will be zero. You can't read anything from it. Cause it's size is always zero. Expression < /dev/zero is used to "close" a commands standard input.



          For saving a process output it produces on standard output you can use command substitution:



          var=$(ssh root@$192.168.80.180 'df -h; free -m' < /dev/null)


          or you can save the standard output of a process by binding it with a file:



          ssh root@$192.168.80.180 'df -h; free -m' < /dev/null > result.txt


          You can read more about bash redirections.



          The line 




          if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then



          is just strange. Just:



          if nc -z 192.168.80.180 22; then


          The if expression is true if the command returns zero status. Comparing commands return status with zero [ $(command; echo $?) -eq 0 ] is just strange.



          More about if.



          Also always quote any expansions (unless you know you don't have to). So quote command substitution [ "$(nc -z ...; echo $?)" -eq 0 ].






          share|improve this answer























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            1














            < /dev/null


            Binds the process standard output with /dev/null file.




            Saving a < /dev/null result ...




            /dev/null is a file and does not produce a result.




            ssh root@$192.168.80.180 'df -h; free -m' < /dev/null



            Runs ssh command with specified parameters and binds it's standard input with /dev/null.



            /dev/null is a magic file. It always has size equal to zero. You can write anything to it. It's size still will be zero. You can't read anything from it. Cause it's size is always zero. Expression < /dev/zero is used to "close" a commands standard input.



            For saving a process output it produces on standard output you can use command substitution:



            var=$(ssh root@$192.168.80.180 'df -h; free -m' < /dev/null)


            or you can save the standard output of a process by binding it with a file:



            ssh root@$192.168.80.180 'df -h; free -m' < /dev/null > result.txt


            You can read more about bash redirections.



            The line 




            if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then



            is just strange. Just:



            if nc -z 192.168.80.180 22; then


            The if expression is true if the command returns zero status. Comparing commands return status with zero [ $(command; echo $?) -eq 0 ] is just strange.



            More about if.



            Also always quote any expansions (unless you know you don't have to). So quote command substitution [ "$(nc -z ...; echo $?)" -eq 0 ].






            share|improve this answer




























              1














              < /dev/null


              Binds the process standard output with /dev/null file.




              Saving a < /dev/null result ...




              /dev/null is a file and does not produce a result.




              ssh root@$192.168.80.180 'df -h; free -m' < /dev/null



              Runs ssh command with specified parameters and binds it's standard input with /dev/null.



              /dev/null is a magic file. It always has size equal to zero. You can write anything to it. It's size still will be zero. You can't read anything from it. Cause it's size is always zero. Expression < /dev/zero is used to "close" a commands standard input.



              For saving a process output it produces on standard output you can use command substitution:



              var=$(ssh root@$192.168.80.180 'df -h; free -m' < /dev/null)


              or you can save the standard output of a process by binding it with a file:



              ssh root@$192.168.80.180 'df -h; free -m' < /dev/null > result.txt


              You can read more about bash redirections.



              The line 




              if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then



              is just strange. Just:



              if nc -z 192.168.80.180 22; then


              The if expression is true if the command returns zero status. Comparing commands return status with zero [ $(command; echo $?) -eq 0 ] is just strange.



              More about if.



              Also always quote any expansions (unless you know you don't have to). So quote command substitution [ "$(nc -z ...; echo $?)" -eq 0 ].






              share|improve this answer


























                1












                1








                1







                < /dev/null


                Binds the process standard output with /dev/null file.




                Saving a < /dev/null result ...




                /dev/null is a file and does not produce a result.




                ssh root@$192.168.80.180 'df -h; free -m' < /dev/null



                Runs ssh command with specified parameters and binds it's standard input with /dev/null.



                /dev/null is a magic file. It always has size equal to zero. You can write anything to it. It's size still will be zero. You can't read anything from it. Cause it's size is always zero. Expression < /dev/zero is used to "close" a commands standard input.



                For saving a process output it produces on standard output you can use command substitution:



                var=$(ssh root@$192.168.80.180 'df -h; free -m' < /dev/null)


                or you can save the standard output of a process by binding it with a file:



                ssh root@$192.168.80.180 'df -h; free -m' < /dev/null > result.txt


                You can read more about bash redirections.



                The line 




                if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then



                is just strange. Just:



                if nc -z 192.168.80.180 22; then


                The if expression is true if the command returns zero status. Comparing commands return status with zero [ $(command; echo $?) -eq 0 ] is just strange.



                More about if.



                Also always quote any expansions (unless you know you don't have to). So quote command substitution [ "$(nc -z ...; echo $?)" -eq 0 ].






                share|improve this answer













                < /dev/null


                Binds the process standard output with /dev/null file.




                Saving a < /dev/null result ...




                /dev/null is a file and does not produce a result.




                ssh root@$192.168.80.180 'df -h; free -m' < /dev/null



                Runs ssh command with specified parameters and binds it's standard input with /dev/null.



                /dev/null is a magic file. It always has size equal to zero. You can write anything to it. It's size still will be zero. You can't read anything from it. Cause it's size is always zero. Expression < /dev/zero is used to "close" a commands standard input.



                For saving a process output it produces on standard output you can use command substitution:



                var=$(ssh root@$192.168.80.180 'df -h; free -m' < /dev/null)


                or you can save the standard output of a process by binding it with a file:



                ssh root@$192.168.80.180 'df -h; free -m' < /dev/null > result.txt


                You can read more about bash redirections.



                The line 




                if [ $(nc -z 192.168.80.180 22; echo $?) -eq 0 ]; then



                is just strange. Just:



                if nc -z 192.168.80.180 22; then


                The if expression is true if the command returns zero status. Comparing commands return status with zero [ $(command; echo $?) -eq 0 ] is just strange.



                More about if.



                Also always quote any expansions (unless you know you don't have to). So quote command substitution [ "$(nc -z ...; echo $?)" -eq 0 ].







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered Nov 27 '18 at 21:06









                Kamil CukKamil Cuk

                11.9k1529




                11.9k1529
































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