Introduction to the Command Line Environment

Open a command window on any computer and the first thing you see is a prompt waiting for input. On its own, the prompt tells you very little. Yet every command you type afterward is interpreted against a location on the disk. Before you can use a command-line tool well, you need to know which location it is looking at. This article answers one question: when you type a command and press return, which folder is the computer working in?

The pattern is always the same. You type a command, the computer carries it out, any results appear in the window, and then a fresh prompt is shown so you can type the next command. Because the window keeps going this way, the location you are working in carries forward from one command to the next. That carried-over location is the subject of the rest of this article.

Think of a command window as a session with a single running state: the location you are standing in. Each command runs against that location, and the location does not reset between commands. A command that looks for a file runs inside the place you are currently standing. A command that moves you somewhere changes that place, and every later command inherits the change.

Keep this picture in mind as we go. The state is the location. The commands are the operations. The prompt, which we will return to shortly, is the window's way of telling you the state before you type the next operation.

Consider a command that refers to a file by a short name such as notes.txt. The name alone does not identify one file on the whole machine, because many folders may each hold a file with that name. The command line resolves short names by looking in one designated folder. That folder is the current directory. Whatever short names you type are understood as names inside that folder.

The current directory is therefore a kind of invisible context attached to your session. It does not appear as a separate file or setting you open. It is simply the answer to the question every command implicitly asks: where should I look for the things you named?

Many command prompts make the current directory easier to spot because the directory name is often displayed as part of the prompt itself. Reading the prompt is the quickest way to check where you are before running anything that depends on location. The source does not fix one exact prompt format, so treat the prompt as a hint and confirm it by listing files when in doubt.

To see what the current directory holds, list its files. On Windows you use dir. On Linux and macOS you use ls. Each command lists the files in the current directory, so the output tells you exactly which short names will resolve right now.

Suppose you run the listing command and see notes.txt among the results. That tells you that a command typing notes.txt with no path will find that file. If notes.txt is not in the list, the same command will not find it from this location, even if a file with that name exists in some other folder on the machine.

When a command window first opens, the current directory is set to your home directory. The home directory is the personal folder of the user, the place where that person's own files are stored. So the first location you work in is not an arbitrary system folder but your own space.

This is why a fresh window is a predictable place to begin. If you want files you saved personally, a newly opened window already points at the folder where they usually live. If you want to work somewhere else, you must move the current directory yourself.

The cd command changes the current directory. You follow cd with the name of the directory you want to move into, then press return. After that, short file names are interpreted inside the new directory, and the prompt usually reflects the new name.

Folders sit inside other folders, forming a tree. The current directory is one node in that tree. When you type a name in cd, that name is read relative to the node you are standing on, not relative to the top of the disk. This is why the same name can point to different folders depending on where you started.

In the diagram, Home is the current directory at the start of a new window. From there, Desktop is a child folder, and the short name Desktop resolves to it. The file notes.txt sits one level further down. A short name for notes.txt only works from inside Desktop, because that is the folder whose files commands reach by short name.