Lesson 08 · pwd - Build a Shell

pwd

The shell always has a current working directory, and `pwd` prints it. It is a small builtin, but you need it today so you can see the effect of `cd` tomorrow.

The goal

Implement the `pwd` builtin so it prints the shell's current working directory.

Start here - the target

TO DO

Scenario: Printing the working directory

Giventhe shell's current working directory is "/tmp"

Whenthe command "pwd" runs

Thenit prints "/tmp" followed by a newline

Andthe last status is 0

Background

Every process has a current working directory - the folder that relative paths are resolved against - and the shell is no exception. pwd (“print working directory”) simply asks the operating system for that path and echoes it. It is about as small as a builtin gets.

Two reasons it comes now. First, it must be a builtin for the same reason cd will be: it reports the shell’s directory, and a child process has its own copy. Second, it is your window onto tomorrow’s work - once cd can change the directory, pwd is how you will confirm it actually moved. Build the observer before the thing it observes.

Make it work

if (strcmp(words[0], "pwd") == 0) {
    char buf[PATH_MAX];
    getcwd(buf, sizeof buf);
    printf("%s\n", buf);
    last_status = 0;
    return;                 // handled as a builtin
}