File types You can have many different types of files, however for the moment, you can consider them to fall into three general groups. You can have programs, text or data files, and shell files. If a file doesn’t contain a program, it can be considered as either text or data. Sometimes it will be simply text, for example if a letter were produced using the edit command. Sometimes it may contain data that isn’t particularly readable to humans, as in a file containing music, sounds, or pictures. If you type the name of such a text or data file, you will get an error message ‘Cannot execute filename:
No such file or directory.’ If you believe a file contains readabletext, you cansee thecontents usingtheinbuilt type filename command. If the file does not contain ordinary text, type will still try to display it, however you may well get a real mess of display characters on your screen. Incidently, you should be cautious about trying to print such non-text files on a printer, as you can waste a lot of paper and upset your printer enough to have to power it down before you can use it again. One special form of text file is a shell program file. This simply contains lines of normal commands, just as they would be typed from the keyboard.
It has the filenameextension ‘ .shell Whenits nameis typed, allthecommands contained within it are executed or run, one by one, just as if you had typed them out at the keyboard. This can be a very convenient way of storing extensive commands that you tend to repeat often. As with ‘ .exec ’ and ‘ .xrel ’ programs, you must not type out the ‘ .shell ’ extension. Filename extensions Programs always have names ending in an ‘extension’. This extension consists ofafullstop‘ . ’followedbyatermsuchas‘ .xrel .exec ’. Youcauseprograms to run by simply typing their name. File names can be either upper or lower case. You must leave off the .xrel or .exec extension when typing their name.
This rule of leaving off the extension follows traditional practice in computer systems, so you may as well get used to it (it does save some typing). For convenience in identifying files, programmers often use names in which a ‘ . is placed in the name, and some agreed upon ‘extension’ is used to end the name. Some extensions you will encounter, and must use correctly, are .exec and .xrel’ , which are programs. Shell programs, which you will learn about in this manual, have ‘ .shell ’ as their extension.
Other common (but not mandatory) extensions are .bas for Basic language source files, .c for C language source files, .doc for program documentation, .f for Forth language source files, .h for header files, .mac for macro definitions, .mus for music files, .s for assembler source files, .snd for sound files, .d , .text , or .doc for various types of text files. Page 32 User Tutorial Manual Files and Directories