The cd command, also known as chdir (change directory), is a command-line OS shell command used to change the current working directory in operating systems such as Unix, DOS, OS/2, AmigaOS (where if a bare path is given, cd is implied), Windows, and Linux. It is also available for use in shell scripts and batch files. The system call that effects the command in most operating systems is chdir(2) that is defined by POSIX.

In computing, the working directory of a process is a directory of a hierarchical file system, if any, dynamically associated with each process. When the process refers to a file using a simple file name or relative path (as opposed to a file designated by a full path from a root directory), the reference is interpreted relative to the current working directory of the process. So for example a process with working directory /rabbit-shoes that asks to create the file foo.txt will end up creating the file /rabbit-shoes/foo.txt.