Linux/Raspberry Pi Script Basics

This document explains the basics of running scripts on Linux/Raspberry Pi.

Quick Answers

Why can’t I just type `visualize_3d.sh`?

You need ./ before the script name:

./visualize_3d.sh

Reason: Linux requires ./ to explicitly tell the system “run this script from the current directory”. This is a security feature - it prevents accidentally running scripts if someone puts a malicious file in your current directory.

Without ./, Linux looks for the script in your PATH (system directories like /usr/bin), not in the current folder.

What does `chmod +x` mean?

chmod +x makes a file executable (able to be run as a program).

What it means:

chmod = “change mode” (file permissions)
+x = “add execute permission”

Why it’s needed:

Linux doesn’t automatically make files executable for security
New files are created without execute permission
You must explicitly give permission to run scripts

When to use it:

Only needed once per file (the first time)
After that, you can run the script anytime with ./script.sh

Why `*.sh` instead of listing files?

The * is a wildcard (pattern matcher) that matches all files ending with .sh.

What *.sh means:

* = matches any filename
.sh = ends with “.sh”

So chmod +x *.sh makes ALL these files executable at once:

visualize_3d.sh
detect_pairs.sh
capture_raspi.sh
setup_venv.sh
etc.

Why use it? Instead of typing:

chmod +x visualize_3d.sh
chmod +x detect_pairs.sh
chmod +x setup_venv.sh
# ... (one line for each file)

You can do them all at once:

chmod +x *.sh

Step-by-Step Example

First Time Setup

Make scripts executable (one-time setup):
```
chmod +x *.sh
```
This makes all .sh files executable (including all run scripts and setup_venv.sh).
Run a program:
```
./visualize_3d.sh
```
Note the ./ before the script name.

Every Time After That

Just run the script directly:

./visualize_3d.sh

You don’t need to run chmod +x again - the permission stays set.

Alternative: Run Without `./`

If you really want to type just visualize_3d.sh (without ./), you can:

Add current directory to PATH (not recommended for security):

export PATH=$PATH:.
visualize_3d.sh  # Now works without ./

Or use the full path (works from anywhere):

/home/user/GitHub/3D-Cam/visualize_3d.sh

But ./visualize_3d.sh is the standard, safe way to do it.

Summary

./ = required to run scripts in current directory
chmod +x = needed once to make files executable
* = wildcard to match multiple files
Only needed once = after chmod +x, you can run scripts anytime