MCS 260 Fall 2020
Week 1 Discussion
A file is a named object that stores data (e.g. a document). Files cannot contain other files.
A directory or folder is a container that stores files & directories.
Both files and folders are often represented by icons.
A full path is a name that uniquely specifies a single file or directory by describing all of the nested directories that contain it.
Example (Windows):
C:\Users\sramanujan\Documents\letter.pdf
Example (Linux/OS X):
/Users/sramanujan/Documents/letter.pdf
Consider the Windows example:
C:\Users\sramanujan\Documents\letter.pdf
"C:" is the drive letter (specifies a storage device)
"\" is the path separator
"Users", "sramanujan", "Documents" are directories, each contained within the previous one
"letter.pdf" is the filename
Icons on the desktop are just files in a certain directory.
In Windows, the desktop for a user named USERNAME is usually:
C:\Users\USERNAME\Desktop
In OS X, it is usually:
/Users/USERNAME/Desktop
In Linux, it is usually:
/home/USERNAME/Desktop
This file on my desktop in Windows:
Has full path:
C:\Users\ddumas\Desktop\hello.py
To run this Python script in Powershell I could use the command:
python C:\Users\ddumas\Desktop\hello.py
Graphical and terminal interfaces have a notion of the working directory.
To show the current working directory (PowerShell, OS X, or Linux):
pwd
(print working directory)
If a filename is given without a full path, its full path is assumed to start with the working directory. This is called a relative path.
Move to a directory described by its full path:
cd C:\Users\ddumas\Desktop
Move to a subdirectory (a directory contained in the working directory):
cd Desktop
Move to the parent directory, i.e. the one that contains the working directory:
cd ..
"cd" works the same way in Windows, OS X, Linux
We want to run hello.py, a script on the desktop.
In PowerShell, with absolute path:
PS C:\Users\ddumas> python C:\Users\ddumas\Desktop\hello.py
Hello world
In PowerShell, with relative path:
PS C:\Users\ddumas> python Desktop\hello.py
Hello world
In PowerShell, first cd to Desktop, then run:
PS C:\Users\ddumas> cd Desktop
PS C:\Users\ddumas\Desktop> python hello.py
Hello world