Directories and Processes

• Processes have two associated directory values
  • A current working directory for relative file access.
  • A root directory for absolute file access.
• The Current working directory.
  • Getting information

    •        #include <unistd.h>
             char *getcwd(char *buf, size_t size);
             char *getwd(char *buf);
             char *get_current_dir_name(void);
      	     

    • The string "(unreachable)" may be returned.
    • getcwd is a posix extension that allocates memory, which must be freed.
  • Changing

    •        #include <unistd.h>
             int chdir(const char *path);
             int fchdir(int fd);
      	     

• The root directory.
  • This determines where / is for the current process.
  • It provides some level of protection, a process can not go outside of it's root directory.
  • This was common for ftp for example.
  • Can only be changed by a privileged process.
  • int chroot(const char *path);
• The real path

  •        #include <limits.h>
           #include <stdlib.h>
    
           char *realpath(const char *path, char *resolved_path);
           

  • Will remove symbolic links, . and .. from a path.
  • And return the actual location.
• Dirname and basename

  •        #include <libgen.h>
           char *dirname(char *path);
           char *basename(char *path);
    	

  • Both do their best to reurn the file and directory parts of a given path.
  • if there is no / dirname returns .
  • Trailing / is ignored by basename.
  • The path "/" causes both to return /
  • for . and .. both return the input.
  • There are two versions, we have discussed the posix version.