Some Code for the Project

• Current Working Directory
  • Each process has a "current working directory"
  • Relative paths are computed from here.
  • It is inherited from the parent process.
• The bash maintains a variable (PWD) contains this value
  • But this is part of bash
  • cd is a bash built-in command
  • It is also an executable.
• pwd
  • This is both a bash built in and an executable.
  • Both will display the current working directory.
• A process can get the value of the working directory
  • char *getcwd(char *buf, size_t size);
    • Copies the absolute pathname to buf if buf is big enough.
    • If buf is NULL, it will allocate a buffer for the name
      • Which the user should free.
    • Returns a pointer to the buffer on success, or NULL on failure
• A process can change the working directory as well:
  • int chdir(const char *path);
    • Returns -1 on error and 0 on success.
    • Changes the CWD to path (if it can)
    • if path starts with / it is absolute
    • otherwise it is relative.
    • ~ does not work here (that is a shell function)
• There are two tools for parsing the directory name.
  • #include <libgen.h>
  • char *dirname(char *path);
  • char *basename(char *path);
  • Be careful, these alter path.
    • They may change the final / in path to be a \0
    • Thus multiple calls to dirname can make a mess of things.
    • They may make a copy of path and return a pointer to statically allocated memory
    • Which may be overwritten by later calls.
    • Paths like "/bin/" have been a problem in the past.
    • But a trailing / no longer counts.
  • basename returns a pointer to everything after the last /
  • dirname returns a pointer to everything before the last /
  • If the path does not contain a /, then dirname returns a .
  • If the path is / both return /
  • If path is NULL or "" both return a .
• There are apparently two versions of basename, depending on if you include <libgen.h> or not.