Linux which cd worked. But cd is a builtin command in bash

Question

I just learned Linux, and read the book "The Linux Command-Line". It says:

cd is a builtin command in bash.

So we cannot find anything with which cd; but somehow it worked well in my computer:

$ which cd
/usr/bin/cd

It is because I use CentOS?

Answer 1

For shell builtins use help rather than man. help cd will give you usage information. which is misleading since it only finds binaries. Use type.

$ type cd
cd is a shell builtin

$ help cd
cd: cd [-L|[-P [-e]] [-@]] [dir]
    Change the shell working directory.
...

Now as it happens, there is a useless binary^* /usr/bin/cd on your system. It's useless both because the shell builtin supercedes it, and because it's impossible for a binary to change the directory of the parent shell. Try to use it and you'll find it does nothing at all.

/dir1$ /usr/bin/cd /dir2
/dir1$