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I have written a very basic shell in C. It reads the input, then runs it using system(lineCopy); (lineCopy being a copy of the input). All commands will run fine in it, other than cd. When I try to cd to a different directory, it simply stays in the current directory. If I try to cd to a directory that doesn't exist, it says, as it should sh: 1: cd: can't cd to /some_nonexistant_directory. When I try to cd to a directory that DOES exist, however, it reads that command, but then stays in the same directory. The variable in which I store the current PWD is continuesly updating, so it cannot be that. All other commands work perfectly. But why does cd not?

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Try changing an environment variable - that will not work either. System inherits the environment and the current working directory. So each system call will inherit the current working directory from its parent.

Ed Heal
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  • OK. Is there something I should replace system(lineCopy); with then? –  Jul 26 '15 at 09:31
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    You cannot - the child does not change the parent in this respect. Anway why write a shell when not going the hole hog – Ed Heal Jul 26 '15 at 09:34
  • … or try defining an alias (and using it on the next line).   … or getting a history listing.   … or putting a command into the background with & and then looking at it with jobs or waiting for it with wait.  … or setting umask.  … or typing exit or logout. – G-Man Says 'Reinstate Monica' Jul 26 '15 at 10:46