Resolve Absolute and Relative Paths

data/observations.csv is not enough information to find anything. It tells you where to go once you already know where you are starting from, and it says nothing about where that is.

Every path gets resolved from a starting point. An absolute path states its own starting point. A relative path borrows one from wherever you currently are.

In a file manager, “wherever you currently are” is the folder whose contents you happen to be looking at right now. That folder gets a proper name once you start typing instructions instead of clicking them: the working directory. One relative path resolved from two different starting folders reaches two different files.

Two routes to one file

Say the working directory is:

/home/sam/Documents/field-notes

Both of these reach the same file:

Absolute: /home/sam/Documents/field-notes/data/observations.csv
Relative: data/observations.csv

The leading / makes the first one absolute; it means the same thing typed from anywhere on the machine. The second starts with data, so resolution begins wherever you are.

Move the working directory to /home/sam/Documents/field-notes/drafts and that same relative path now looks for a data directory inside drafts. There isn’t one. The path did not change; its meaning did.

To reach the real data from there, go up first:

../data/observations.csv

Two dots, .., mean the parent directory. One dot, ., means the current one, which is why ./data/observations.csv and data/observations.csv land in the same place.

The diagram below traces both starting points to the same absolute file: first from field-notes, then from drafts.

The destination never moved. Only the directions changed because your starting point did.

The same reasoning on Windows

Working directory:

C:\Users\Sam\Documents\field-notes

Both reach the file:

Absolute: C:\Users\Sam\Documents\field-notes\data\observations.csv
Relative: data\observations.csv

The drive letter plus the backslash after the colon is what makes the first absolute. C:data\observations.csv is missing that backslash and is not a complete drive-rooted path. Write C:\... when you mean absolute and the ambiguity never comes up.

From C:\Users\Sam\Documents\field-notes\drafts:

..\data\observations.csv

Resolve a path on paper

Do this before you ask a command to change anything, and keep doing it until it becomes automatic:

1. Write down the working directory.

2. Decide whether the path resets to a root or starts where you are.

3. Take each segment left to right. Stay put for ., go up for .., descend for a name.

4. Write down where you landed, and compare it to where you meant to land.

Try it. Working directory C:\Users\Sam\Documents\field-notes\data\raw, path ..\..\drafts\outline.txt:

Start:  C:\Users\Sam\Documents\field-notes\data\raw
..      C:\Users\Sam\Documents\field-notes\data
..      C:\Users\Sam\Documents\field-notes
drafts  C:\Users\Sam\Documents\field-notes\drafts
target: C:\Users\Sam\Documents\field-notes\drafts\outline.txt

That takes four lines and no guessing, and it works the same way on every platform.

If the same relative spelling behaves differently today, a changed working directory is one possible cause. Compare today’s starting point and the target tree before moving anything. A path resolved from the wrong place may reach a different target, or it may name nothing at all; either result is evidence about where the route first stopped matching.

You have done all of this without touching a shell. The last lesson of the chapter puts it to work on a project you will still be able to find in six months.