Folders and the Path

1Where am I?

pwd ("print working directory") shows the current folder, the same one named at the top of the Current Folder panel. ls lists what is inside it.

pwd
ls

2Moving between folders

cd ("change directory") moves into a folder. cd .. goes up one level. Double-clicking a folder in the Current Folder panel does the same thing.

cd psych390
ls
cd data
ls
cd ..
pwd

cd data is a relative path: it starts from wherever you are. A full path starts from the top of the disk and works from anywhere. On a Mac it starts with /Users/; on Windows it starts with a drive letter, like C:\Users\.

cd /Users/student/Documents/MATLAB/psych390

3Why the current folder matters for data

A file name without a full path is looked up in the current folder. The same command can find a file from one folder and miss it from another.

isfile('data/sub-01.set')
cd ..
isfile('data/sub-01.set')
cd psych390

fullfile joins folder and file names with the right separator for the computer, which keeps a script working on both Mac and Windows.

fullfile('data', 'sub-01.set')

4The search path

Functions are files too: mean is a file called mean.m. When you type a name, MATLAB checks the current folder, then each folder on its search path in order (the Path panel). MATLAB's own functions are always on the path. EEGLAB's are not until you add them.

which mean
which eeglab
eeglab

5Putting EEGLAB on the path

addpath adds a folder to the path. Give it the full path to the EEGLAB folder you downloaded; the version number in the name will match your download. Then run eeglab, and it adds its own subfolders. Watch the Path panel as you go.

addpath('/Users/student/Documents/MATLAB/eeglab2025.1')
which eeglab
which pop_loadset
eeglab
which pop_loadset

pop_loadset lives in a subfolder (functions/popfunc), so MATLAB could not find it until eeglab ran and added that subfolder.

6Making it stick

MATLAB forgets addpath changes when it quits. savepath (or Save in the Set Path window, opened with pathtool) keeps them for next time. On a shared lab computer you may not be allowed to save the path. Then put the addpath line at the top of your script instead.

savepath