How does `cd` work?

Re:How does `cd` work? by kazinator on Thursday March 01, 2018 @06:52PM (#16497519)

> The cd builtin is invoked as part of the Bash shell.

> The Bash shell invokes the chdir function.

Nope! Not quite.

Bash:

  ~$ ls -ld foo
  lrwxrwxrwx 1 kaz kaz 4 Mar  1 6:50 foo -> /etc
  ~$ cd foo
  ~/foo$ pwd
  /home/kaz/foo
  ~/foo$ cd ..
  ~$ pwd
  /home/kaz

Raw chdir and getcwd syscalls:

  $ pwd
  /home/kaz
  $ txr
  This is the TXR Lisp interactive listener of TXR 190.
  Quit with :quit or Ctrl-D on empty line. Ctrl-X ? for cheatsheet.
  1> (chdir "foo")
  t
  2> (pwd)
  "/etc"
  3> (chdir "..")
  t
  4> (pwd)
  "/"

See the difference? While of course the shell will invoke chdir, it has its own idea of a current working directory, and translates the argument of cd to something else. For instance cd .. doesn't translate to (chdir "..").

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Re:How does `cd` work? by wodenokoto on Friday March 02, 2018 @02:23AM (#16499755)

She says that it is all a ton of functions that sanitize input and implement logic before calling chdir.

So the article does point out that CD isn't a direct alias for chdir

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