.SH "How is Information Stored on the Machine?" .P Information is stored on the machine in files. A file can store the data which is to be operated on in some way by a program or a file can contain a program which acts on data. (Even a terminal is considered by the system to be a file.) .P Every file is denoted by a unique name which can be up to 14 characters long. The characters may be non-alphanumeric (eg. '-', '.', ...), but a word of warning! Some files are generally used for temporary storage only, and are removed every night. If you create a file called "temp*"\*F or "a.out" for instance, .FS by "temp*" I mean any file name beginning with "temp". .FE it will be removed during the night, so don't have valuable information in any file with the above names\*F. .FS all the following files are removed nightly, *.map, *.lst, *.l, tmp*, temp*, core, a.out, TEMP*, RTEMP*, STEMP*. .FE .P Don't get alarmed if another user uses the same name for one of his files as you do. They are considered by the system to be distinct because they are in different accounts. .H 2 "What Files Do You Have?" To find the names of all your files, just type .DS % ls .DE and a list of the file names will appear in alphabetical order, like the following .DS O T back mult regs run sim85 sim85c sys.s temp .DE If you have so many files that the list goes off the screen, or if you want a concise listing then try .DS % ls ^ mc .DE and the list of files will be printed for you in columns: .DS ~~~~~~~~O~~~~~~~T~~~~~~~back~~~~mult~~~~regs~~~~run~~~~~sim85~~~sim85c ~~~~~~~~sys.s~~~temp .DE More information about files will be found in the sections "Common Commands" and "Advanced Usage". .H 2 "The Contents of a File" There are several ways in which the contents of a file may be seen. If you want to see a file quickly with a minimum of fuss you should use a program called "cat". To see the contents of your file called "fred2" type .DS % cat fred2 .DE and you will get .DS O T back fred fred2 mult regs run sim85 sim85c sys.s % .DE which is, you will recall, a listing of all your files. You can also see several files at once, for example, by typing .DS % cat fred fred2 .DE and you will get .DS This is a test hello world, this is Unix Editor O T back fred fred2 mult regs run sim85 sim85c sys.s % .DE .P "pr" will print files in a manner best suited to hard copy (or non-display type) terminals. Every page has a heading, page number and the date. There are 51 lines to one DECwriter page, so to print "fred" you type .DS % pr -l51 fred\*F .DE .FS please note the argument is the letter 'l' not the digit '1'. The 'l' stands for 'lines per page'. .FE The -l51 tells "pr" that there are 51 lines to one page. After typing the above command the following will be printed .DS Nov 28 13:16 1978 fred Page 1 This is a test hello world, this is Unix Editor ( + 47 blank lines ) .DE If this file had been much longer then the date etc. would appear at the top of every page .P The previous two commands are useful when you wish to see what's in a file when you are at a terminal. The third method of viewing files is to use the command "lpr". This is especially useful if the files are large. If you type .DS % lpr fred .DE the terminal will respond .DS % .DE but you haven't got a listing to see. The listing of "fred" will be sent to a large, high-speed printer called a "line printer" (hence the name "lpr"). The line printer at the AGSM is located in room 410 at the opposite end of the floor to the AGSM library. When you pick up your listing from the line printer room there will be a "header" on the first page which contains, among other things, your login name. .P When you pick up your listing from the line printer, it is possible that there will be several other users' listings there also. If this is the case then you are requested to separate all the listings and place them in the shelving provided. Treat other peoples' listings as you would have them treat yours. .P This third form of listing is very useful when the file is very long or a permanent listing is required. To "lpr" your two files just type .DS % lpr fred fred2 .DE and the line printer will produce a listing with a header, and then the two files, both beginning on new pages. .P If you wanted the formatting that "pr" offers and would like it on the line printer then type .DS % pr fred ^ lpr\*F .DE .FS the symbol "^" denotes a 'pipe' and will be explained later. .FE and you will get a listing of what "pr" produces on the line printer. .H 2 "Differences Between Files" .P There are two types of files. The first type of files are text files which have printable characters on them, and are generally used for human consumption or input to programs. The second type of file are those which contain machine instructions (i.e. programs) and do not appear to contain useful information. These files are usually called "binary files". .P All binary files, when printed on the screen, will produce garbage, blanking the screen quite often. When you lpr a binary file the line printer will just print a few characters at the beginning of a new page. It will do this perhaps two hundred times, hence wasting many sheets of paper. \&'lpr'ing binary files is not regarded as a joke as it wastes a lot of paper, so be careful of which files you lpr.