Running Programs From the Terminal
The terminal is where your code comes to life. Writing code creates a file; running it makes the computer actually execute your instructions. Understanding this execution process helps you debug problems and work more effectively.
Running Python Scripts
To run a Python file, use the python3 command followed by the filename:
On Windows, you might use python instead of python3:
python hello.py
Make sure you're in the same folder as your script, or provide the full path: python3 /path/to/hello.py.
Running JavaScript With Node.js
For JavaScript files, use the node command:
What Happens When You Run a Program
When you execute a command like python3 script.py, several things happen:
- The shell finds the program — It locates the Python interpreter on your system
- The interpreter loads your file — Your code is read from disk into memory
- Instructions execute — The interpreter processes your code line by line
- Output appears — Any
print()statements display in the terminal - The program ends — Control returns to the terminal prompt
This entire process might take milliseconds for simple scripts.
Understanding Exit Codes
Every program finishes with an exit code — a number indicating success or failure:
- 0 — Success (everything worked)
- Non-zero — Error (something went wrong)
You usually don't see exit codes directly, but they matter for automation and scripting. You can check the last exit code:
echo $? # Shows exit code of last command
$LASTEXITCODE # Shows exit code in PowerShell
When Things Go Wrong
If your program has an error, you'll see an error message instead of normal output:
These error messages tell you what went wrong and where. Learning to read them is a crucial debugging skill you'll develop throughout this track.
The Execution Cycle
As a developer, you'll repeat this cycle constantly: edit code, save, run, observe results, repeat. The terminal makes this cycle fast and efficient — no clicking through menus, just type and run.