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(12) File System

Storing Information -- The File System

UNIX stores information in files. Files can be named almost anything.
File names
Files and directories (folders) can be named almost anything, as long as they do not contain "/" (since it has to separate directories in a path). In practice, many programs will get confused if filenames contain spaces and certain punctuation characters. Safe characters are [a-zA-Z0-9-_.]. Mixed case is allowed and all operations are case sensitive (unlike Mac and Windows). In particular, " and ' can be placed in filenames easily on Macs and then transferred to Unix - legal, but can cause headaches. Some old Unix systems had a 14-character limit; current ones have essentially no limit. Macs and Windows have a 32-character limit. Macs and Windows preserve case for display, but internally treat upper and lower case as the same.
The file system structure (as seen by the user) is similar to the hierarchical DOS and Mac file system structure.
The top file for the mac is the "desktop" file, for DOS/Windows it is the drive (C:,D: etc.) and for UNIX it's "/" which is usually called root.
All disks etc. are attached (mounted) somewhere below the root. Users usually do not need to know or care which disk their files are actually on, only the mount point, which determines the full path name to a file.
Everything in Unix is a file. Direct access to hardware (printers, tape drives etc.) and logical devices is made through special files. Most of these device interface files live in /dev.
When you are logged on to UNIX you always have a location in the file system which is your current working directory. Filenames are assumed to be in this current working directory, unless some other directory is explicitly named. (More on this later)

ls: The ls command lists files in a directory, and various information about the files. You will use this a lot.
ls -l: The -l flag (long) lists most of the information stored about a file.

slide13.src last modified Jan 31, 2011

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