Will the inherited environment variables be inherited as environment variables or as shell variables?

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Say my bash shell have the following environment variable:



export a="Hello World"


If I executed a process from the bash shell, the a environment variable will be inherited by this child process.



My question is: will a be inherited by the child process as an environment variable or as a shell variable, that is, will a in the child process be exported?










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    up vote
    1
    down vote

    favorite












    Say my bash shell have the following environment variable:



    export a="Hello World"


    If I executed a process from the bash shell, the a environment variable will be inherited by this child process.



    My question is: will a be inherited by the child process as an environment variable or as a shell variable, that is, will a in the child process be exported?










    share|improve this question























      up vote
      1
      down vote

      favorite









      up vote
      1
      down vote

      favorite











      Say my bash shell have the following environment variable:



      export a="Hello World"


      If I executed a process from the bash shell, the a environment variable will be inherited by this child process.



      My question is: will a be inherited by the child process as an environment variable or as a shell variable, that is, will a in the child process be exported?










      share|improve this question













      Say my bash shell have the following environment variable:



      export a="Hello World"


      If I executed a process from the bash shell, the a environment variable will be inherited by this child process.



      My question is: will a be inherited by the child process as an environment variable or as a shell variable, that is, will a in the child process be exported?







      linux environment-variables






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      asked Sep 24 '17 at 19:53









      user7681202

      237414




      237414




















          2 Answers
          2






          active

          oldest

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          up vote
          3
          down vote



          accepted










          As an environment variable.



          This means that any child process that the child process starts will inherit the variable as well.



          Testing:



          $ export FOO=bar
          $ sh
          $ sh
          $ sh
          $ echo "$FOO"
          bar
          $ exit
          $ exit
          $ exit


          Above, the shell creating the environment variable FOO started a new interactive shell. That started another one, and that one started another one. Within this great-grandchild shell, $FOO has the value bar.



          Another test showing that if if a subshell changes the environment variable, the change is carried over into later subshells (but is not propagated to the parent shells):



          $ export FOO=bar
          $ ( ( echo "$FOO"; FOO=quux; ( ( ( echo "$FOO" ) ) ) ) )
          bar
          quux
          $ echo "$FOO"
          bar


          (in this example, it doesn't matter that FOO is exported as ( ... ) subshells also inherit shell variables, but the the effect would have been the same had each ( ... ) been a totally separate process)



          Note that environment variables are available to any process started from the shell, not just shell scripts. It would not make sense for a C program or awk script to inherit them as shell variables as there is no concept of these kinds of variables in those languages (environment variables are strictly key-value pairs, whereas shell variables may be typed as integers, read-only, arrays, associative arrays, etc., depending on the capabilities of the shell).






          share|improve this answer





























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            You can read your process environmental variables from /proc/PID/environ. So when you export variable, it is stated in this /proc "file".






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              2 Answers
              2






              active

              oldest

              votes








              2 Answers
              2






              active

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              active

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              active

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              up vote
              3
              down vote



              accepted










              As an environment variable.



              This means that any child process that the child process starts will inherit the variable as well.



              Testing:



              $ export FOO=bar
              $ sh
              $ sh
              $ sh
              $ echo "$FOO"
              bar
              $ exit
              $ exit
              $ exit


              Above, the shell creating the environment variable FOO started a new interactive shell. That started another one, and that one started another one. Within this great-grandchild shell, $FOO has the value bar.



              Another test showing that if if a subshell changes the environment variable, the change is carried over into later subshells (but is not propagated to the parent shells):



              $ export FOO=bar
              $ ( ( echo "$FOO"; FOO=quux; ( ( ( echo "$FOO" ) ) ) ) )
              bar
              quux
              $ echo "$FOO"
              bar


              (in this example, it doesn't matter that FOO is exported as ( ... ) subshells also inherit shell variables, but the the effect would have been the same had each ( ... ) been a totally separate process)



              Note that environment variables are available to any process started from the shell, not just shell scripts. It would not make sense for a C program or awk script to inherit them as shell variables as there is no concept of these kinds of variables in those languages (environment variables are strictly key-value pairs, whereas shell variables may be typed as integers, read-only, arrays, associative arrays, etc., depending on the capabilities of the shell).






              share|improve this answer


























                up vote
                3
                down vote



                accepted










                As an environment variable.



                This means that any child process that the child process starts will inherit the variable as well.



                Testing:



                $ export FOO=bar
                $ sh
                $ sh
                $ sh
                $ echo "$FOO"
                bar
                $ exit
                $ exit
                $ exit


                Above, the shell creating the environment variable FOO started a new interactive shell. That started another one, and that one started another one. Within this great-grandchild shell, $FOO has the value bar.



                Another test showing that if if a subshell changes the environment variable, the change is carried over into later subshells (but is not propagated to the parent shells):



                $ export FOO=bar
                $ ( ( echo "$FOO"; FOO=quux; ( ( ( echo "$FOO" ) ) ) ) )
                bar
                quux
                $ echo "$FOO"
                bar


                (in this example, it doesn't matter that FOO is exported as ( ... ) subshells also inherit shell variables, but the the effect would have been the same had each ( ... ) been a totally separate process)



                Note that environment variables are available to any process started from the shell, not just shell scripts. It would not make sense for a C program or awk script to inherit them as shell variables as there is no concept of these kinds of variables in those languages (environment variables are strictly key-value pairs, whereas shell variables may be typed as integers, read-only, arrays, associative arrays, etc., depending on the capabilities of the shell).






                share|improve this answer
























                  up vote
                  3
                  down vote



                  accepted







                  up vote
                  3
                  down vote



                  accepted






                  As an environment variable.



                  This means that any child process that the child process starts will inherit the variable as well.



                  Testing:



                  $ export FOO=bar
                  $ sh
                  $ sh
                  $ sh
                  $ echo "$FOO"
                  bar
                  $ exit
                  $ exit
                  $ exit


                  Above, the shell creating the environment variable FOO started a new interactive shell. That started another one, and that one started another one. Within this great-grandchild shell, $FOO has the value bar.



                  Another test showing that if if a subshell changes the environment variable, the change is carried over into later subshells (but is not propagated to the parent shells):



                  $ export FOO=bar
                  $ ( ( echo "$FOO"; FOO=quux; ( ( ( echo "$FOO" ) ) ) ) )
                  bar
                  quux
                  $ echo "$FOO"
                  bar


                  (in this example, it doesn't matter that FOO is exported as ( ... ) subshells also inherit shell variables, but the the effect would have been the same had each ( ... ) been a totally separate process)



                  Note that environment variables are available to any process started from the shell, not just shell scripts. It would not make sense for a C program or awk script to inherit them as shell variables as there is no concept of these kinds of variables in those languages (environment variables are strictly key-value pairs, whereas shell variables may be typed as integers, read-only, arrays, associative arrays, etc., depending on the capabilities of the shell).






                  share|improve this answer














                  As an environment variable.



                  This means that any child process that the child process starts will inherit the variable as well.



                  Testing:



                  $ export FOO=bar
                  $ sh
                  $ sh
                  $ sh
                  $ echo "$FOO"
                  bar
                  $ exit
                  $ exit
                  $ exit


                  Above, the shell creating the environment variable FOO started a new interactive shell. That started another one, and that one started another one. Within this great-grandchild shell, $FOO has the value bar.



                  Another test showing that if if a subshell changes the environment variable, the change is carried over into later subshells (but is not propagated to the parent shells):



                  $ export FOO=bar
                  $ ( ( echo "$FOO"; FOO=quux; ( ( ( echo "$FOO" ) ) ) ) )
                  bar
                  quux
                  $ echo "$FOO"
                  bar


                  (in this example, it doesn't matter that FOO is exported as ( ... ) subshells also inherit shell variables, but the the effect would have been the same had each ( ... ) been a totally separate process)



                  Note that environment variables are available to any process started from the shell, not just shell scripts. It would not make sense for a C program or awk script to inherit them as shell variables as there is no concept of these kinds of variables in those languages (environment variables are strictly key-value pairs, whereas shell variables may be typed as integers, read-only, arrays, associative arrays, etc., depending on the capabilities of the shell).







                  share|improve this answer














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                  edited Sep 24 '17 at 20:30

























                  answered Sep 24 '17 at 20:04









                  Kusalananda

                  106k14209327




                  106k14209327






















                      up vote
                      0
                      down vote













                      You can read your process environmental variables from /proc/PID/environ. So when you export variable, it is stated in this /proc "file".






                      share|improve this answer
























                        up vote
                        0
                        down vote













                        You can read your process environmental variables from /proc/PID/environ. So when you export variable, it is stated in this /proc "file".






                        share|improve this answer






















                          up vote
                          0
                          down vote










                          up vote
                          0
                          down vote









                          You can read your process environmental variables from /proc/PID/environ. So when you export variable, it is stated in this /proc "file".






                          share|improve this answer












                          You can read your process environmental variables from /proc/PID/environ. So when you export variable, it is stated in this /proc "file".







                          share|improve this answer












                          share|improve this answer



                          share|improve this answer










                          answered Sep 24 '17 at 20:09









                          Jaroslav Kucera

                          4,3904621




                          4,3904621



























                               

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