Does cd . have use?












2















One of the tutorials I've been following briefly stated that cd . has no use. When trying to replicate issue shown by OP in Symbolic link recursion - what makes it “reset”?, I also tried cd ., which showed the same effect OP described (growing $PWD variable), which can be countered with cd -P.



This makes me wonder, is there any case where one does in fact would want to use cd . ?






cd-command







share|improve this question



























    2















    One of the tutorials I've been following briefly stated that cd . has no use. When trying to replicate issue shown by OP in Symbolic link recursion - what makes it “reset”?, I also tried cd ., which showed the same effect OP described (growing $PWD variable), which can be countered with cd -P.



    This makes me wonder, is there any case where one does in fact would want to use cd . ?






    cd-command







    share|improve this question

























      2












      2








      2








      One of the tutorials I've been following briefly stated that cd . has no use. When trying to replicate issue shown by OP in Symbolic link recursion - what makes it “reset”?, I also tried cd ., which showed the same effect OP described (growing $PWD variable), which can be countered with cd -P.



      This makes me wonder, is there any case where one does in fact would want to use cd . ?






      cd-command







      share|improve this question














      One of the tutorials I've been following briefly stated that cd . has no use. When trying to replicate issue shown by OP in Symbolic link recursion - what makes it “reset”?, I also tried cd ., which showed the same effect OP described (growing $PWD variable), which can be countered with cd -P.



      This makes me wonder, is there any case where one does in fact would want to use cd . ?






      cd-command




      cd-command






      share|improve this question













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      asked 2 hours ago









      Sergiy KolodyazhnyySergiy Kolodyazhnyy

      8,70912355




      8,70912355






















          2 Answers
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          The path of directory could have changed since the last executed command and without cd . bash and ksh93 shells will rely on logical working directory described in the linked post in the question; so calling cd . which makes the shell issue getcwd() syscall, will ensure your current path is still valid.



          Steps to reproduce in bash:




          1. in terminal tab issue mkdir ./dir_no_1; cd ./dir_no_1

          2. in different terminal tab issue mv dir_no_1 dir_no_2

          3. issue in first terminal tab echo $PWD and pwd. Notice that the directory has been externally renamed, shell's environment has not been updated.

          4. issue cd .; pwd; echo $PWD. Notice the value will be updated.


          ksh93, however, does not update the environment information, so cd . in ksh93 may in fact be useless. In /bin/dash on Ubuntu and other Debian based systems, cd . returns dash: 3: cd: can't cd to . error, however cd -P . works ( unlike in ksh93 ).






          share|improve this answer































            2














            I think this is overthinking the problem. cd . may not be something that one would manually run in the usual course of things, but it definitely is something that can come up in programmatic execution (think of any situation where you might cd to the directory containing a file, whose path is supplied by the user). Therefore, it doesn't have to have some specific use: as long as it fulfills the usual semantics of cd <some-path>, it is useful.






            share|improve this answer
























            • Agreed, . should be treated as a valid path specified by cd syntax just fine.

              – Sergiy Kolodyazhnyy
              1 hour ago











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            2 Answers
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            2 Answers
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            2














            The path of directory could have changed since the last executed command and without cd . bash and ksh93 shells will rely on logical working directory described in the linked post in the question; so calling cd . which makes the shell issue getcwd() syscall, will ensure your current path is still valid.



            Steps to reproduce in bash:




            1. in terminal tab issue mkdir ./dir_no_1; cd ./dir_no_1

            2. in different terminal tab issue mv dir_no_1 dir_no_2

            3. issue in first terminal tab echo $PWD and pwd. Notice that the directory has been externally renamed, shell's environment has not been updated.

            4. issue cd .; pwd; echo $PWD. Notice the value will be updated.


            ksh93, however, does not update the environment information, so cd . in ksh93 may in fact be useless. In /bin/dash on Ubuntu and other Debian based systems, cd . returns dash: 3: cd: can't cd to . error, however cd -P . works ( unlike in ksh93 ).






            share|improve this answer




























              2














              The path of directory could have changed since the last executed command and without cd . bash and ksh93 shells will rely on logical working directory described in the linked post in the question; so calling cd . which makes the shell issue getcwd() syscall, will ensure your current path is still valid.



              Steps to reproduce in bash:




              1. in terminal tab issue mkdir ./dir_no_1; cd ./dir_no_1

              2. in different terminal tab issue mv dir_no_1 dir_no_2

              3. issue in first terminal tab echo $PWD and pwd. Notice that the directory has been externally renamed, shell's environment has not been updated.

              4. issue cd .; pwd; echo $PWD. Notice the value will be updated.


              ksh93, however, does not update the environment information, so cd . in ksh93 may in fact be useless. In /bin/dash on Ubuntu and other Debian based systems, cd . returns dash: 3: cd: can't cd to . error, however cd -P . works ( unlike in ksh93 ).






              share|improve this answer


























                2












                2








                2







                The path of directory could have changed since the last executed command and without cd . bash and ksh93 shells will rely on logical working directory described in the linked post in the question; so calling cd . which makes the shell issue getcwd() syscall, will ensure your current path is still valid.



                Steps to reproduce in bash:




                1. in terminal tab issue mkdir ./dir_no_1; cd ./dir_no_1

                2. in different terminal tab issue mv dir_no_1 dir_no_2

                3. issue in first terminal tab echo $PWD and pwd. Notice that the directory has been externally renamed, shell's environment has not been updated.

                4. issue cd .; pwd; echo $PWD. Notice the value will be updated.


                ksh93, however, does not update the environment information, so cd . in ksh93 may in fact be useless. In /bin/dash on Ubuntu and other Debian based systems, cd . returns dash: 3: cd: can't cd to . error, however cd -P . works ( unlike in ksh93 ).






                share|improve this answer













                The path of directory could have changed since the last executed command and without cd . bash and ksh93 shells will rely on logical working directory described in the linked post in the question; so calling cd . which makes the shell issue getcwd() syscall, will ensure your current path is still valid.



                Steps to reproduce in bash:




                1. in terminal tab issue mkdir ./dir_no_1; cd ./dir_no_1

                2. in different terminal tab issue mv dir_no_1 dir_no_2

                3. issue in first terminal tab echo $PWD and pwd. Notice that the directory has been externally renamed, shell's environment has not been updated.

                4. issue cd .; pwd; echo $PWD. Notice the value will be updated.


                ksh93, however, does not update the environment information, so cd . in ksh93 may in fact be useless. In /bin/dash on Ubuntu and other Debian based systems, cd . returns dash: 3: cd: can't cd to . error, however cd -P . works ( unlike in ksh93 ).







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered 2 hours ago









                Sergiy KolodyazhnyySergiy Kolodyazhnyy

                8,70912355




                8,70912355

























                    2














                    I think this is overthinking the problem. cd . may not be something that one would manually run in the usual course of things, but it definitely is something that can come up in programmatic execution (think of any situation where you might cd to the directory containing a file, whose path is supplied by the user). Therefore, it doesn't have to have some specific use: as long as it fulfills the usual semantics of cd <some-path>, it is useful.






                    share|improve this answer
























                    • Agreed, . should be treated as a valid path specified by cd syntax just fine.

                      – Sergiy Kolodyazhnyy
                      1 hour ago
















                    2














                    I think this is overthinking the problem. cd . may not be something that one would manually run in the usual course of things, but it definitely is something that can come up in programmatic execution (think of any situation where you might cd to the directory containing a file, whose path is supplied by the user). Therefore, it doesn't have to have some specific use: as long as it fulfills the usual semantics of cd <some-path>, it is useful.






                    share|improve this answer
























                    • Agreed, . should be treated as a valid path specified by cd syntax just fine.

                      – Sergiy Kolodyazhnyy
                      1 hour ago














                    2












                    2








                    2







                    I think this is overthinking the problem. cd . may not be something that one would manually run in the usual course of things, but it definitely is something that can come up in programmatic execution (think of any situation where you might cd to the directory containing a file, whose path is supplied by the user). Therefore, it doesn't have to have some specific use: as long as it fulfills the usual semantics of cd <some-path>, it is useful.






                    share|improve this answer













                    I think this is overthinking the problem. cd . may not be something that one would manually run in the usual course of things, but it definitely is something that can come up in programmatic execution (think of any situation where you might cd to the directory containing a file, whose path is supplied by the user). Therefore, it doesn't have to have some specific use: as long as it fulfills the usual semantics of cd <some-path>, it is useful.







                    share|improve this answer












                    share|improve this answer



                    share|improve this answer










                    answered 1 hour ago









                    OlorinOlorin

                    1,799313




                    1,799313













                    • Agreed, . should be treated as a valid path specified by cd syntax just fine.

                      – Sergiy Kolodyazhnyy
                      1 hour ago



















                    • Agreed, . should be treated as a valid path specified by cd syntax just fine.

                      – Sergiy Kolodyazhnyy
                      1 hour ago

















                    Agreed, . should be treated as a valid path specified by cd syntax just fine.

                    – Sergiy Kolodyazhnyy
                    1 hour ago





                    Agreed, . should be treated as a valid path specified by cd syntax just fine.

                    – Sergiy Kolodyazhnyy
                    1 hour ago


















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