Lesson 10 · cd with no argument, and cd -

cd with no argument, and cd -

Bare `cd` takes you home, and `cd -` takes you back where you were. Today you add those two shortcuts, which means tracking the previous directory as the shell moves.

The goal

Make `cd` with no argument go to HOME, and `cd -` return to the previous directory (OLDPWD) and print it.

Start here - the target

TO DO

Scenario: Special cd destinations

GivenHOME is "/home/me" and the current directory is "/tmp"

Whena bare "cd" runs

Thenthe working directory becomes "/home/me"

Andrunning "cd -" afterward returns to "/tmp" and prints "/tmp"

Background

Two shortcuts make cd pleasant to live in. A bare cd with no argument takes you to your home directory, read from the HOME environment variable - the everyday “take me home” gesture. And cd - returns you to wherever you just were and prints that path, so you can bounce between two directories without retyping either.

cd - only works if the shell remembers the previous directory. The trick is to record your current location into a saved “old directory” (OLDPWD) just before every successful move. Then - simply means “the saved old directory,” and moving there naturally saves your current spot as the next OLDPWD. One small piece of bookkeeping unlocks both shortcuts.

Make it work

char *target = words[1];
if (target == NULL)            target = getenv("HOME");
else if (strcmp(target,"-")==0) target = oldpwd;   // and print it
getcwd(oldpwd, sizeof oldpwd);  // remember where we were, before moving
chdir(target);

CheckpointDONE

`cd` alone goes home and `cd -` jumps back. Commit and stop here.