pwd

PWD is an acronym commonly used in Unix-like environments to denote the present working directory. It can refer to two related concepts: the environment variable named PWD that stores a path, and the pwd command (or shell builtin) that prints the current directory.

The PWD environment variable is maintained by the shell and is updated as the user changes directories with the cd command. It generally contains the absolute path of the current directory and is inherited by child processes. However, if the directory is changed outside the shell, the variable can become stale. For robust scripts, rely on a command such as pwd to determine the current directory, and be aware of the -L versus -P options when applicable.

The pwd command prints the current working directory. In GNU coreutils, it supports -L and -P: -L prints the logical path, i.e., the path as stored in PWD, including symbolic links as they appear to the user; -P prints the physical path, resolving all symbolic links to their real locations. The default is typically -L. In many shells, pwd is also a builtin with similar options.

Logical versus physical: The logical path reflects the path as seen by the user (including symbolic links) if the shell tracks PWD; the physical path reflects the actual directory on disk with all symlinks resolved. For example, if /home/user/links/dir is a symlink to /mnt/data/real, cd /home/user/links/dir and run pwd -L might yield /home/user/links/dir, while pwd -P would yield /mnt/data/real.

Related concepts include OLDPWD, which stores the previous directory, and HOME, the user's home directory. PWD behavior can vary between shells and environments, so understanding the distinction between the environment variable and the pwd command helps in scripting and navigation.