An Operating Systems Vade Mecum

Utility programs 249be misunderstood. For example, for very obvious syntax errors, one compiler generatesthe message, ‘‘The details of this error can be found in your code.’’ Themessage is not very helpful, even if it is cute.Different interactive programs should use similar commands. It can be confusingif the termination command is quit for one program, exit for another, andZZ for a third.3 UTILITY PROGRAMSThe command interpreter utility is important because every user needs to deal with it.Other utility programs are also important for various classes of users. The success of anoperating system often depends on the quality of these utility programs. We will mentiona number of these programs here but will not dwell on their organization or their features.3.1 Document preparationOn many computers, a very large proportion of a user’s time is spent preparing documentsof all sorts. Documents range from memos to technical reports, user guides, andbooks. This book itself was composed with the aid of tools provided by the BSD Unixoperating system.At the moment this sentence was composed, 15 out of 47 user processes were runninga text-editing program. The text editor is often the first program invoked to build adocument. A text editor is an interactive program that allows the user to create andmodify text files. Some editors show only one line of the file at a time; others use a fulldisplay. The most advanced editors use bit-mapped displays and can show several windowsinto one file or several files at the same time. Such editors can sometimes embedpictures into the middle of text files.Once a document has been entered into a file, spelling checkers and style checkerscan be useful. Spelling checkers complain if they can’t find words in their dictionary,and most understand common prefixes and suffixes. A few will suggest a menu ofrespellings of disputed words and will accept new words to be added to the dictionary.Style checkers detect potentially poor usages, such as ‘‘a number of’’ or ‘‘the fact that,’’which might be improved by rewriting. Style checkers can also report the percentage ofnouns and verbs used.The next step is often a text-formatting program. Text formatters can produce outputacceptable to a wide variety of devices, including display screens, line printers, highresolutiondot-matrix printers, and phototypesetters. These programs usually take sourcefiles that contain both text and formatting commands, such as ‘‘start new paragraph,’’‘‘number every page,’’ ‘‘don’t hyphenate,’’ and ‘‘make wide columns.’’ Sometimesthese programs can format mathematical formulas, tables, footnotes, bibliographic