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55 | <H3><A NAME="SECTION0082112000000000000000"></A><A NAME="optparse-what-options-for"></A> | |
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57 | 6.21.1.2 What are options for? | |
58 | </H3> | |
59 | ||
60 | <P> | |
61 | Options are used to provide extra information to tune or customize the | |
62 | execution of a program. In case it wasn't clear, options are usually | |
63 | <em>optional</em>. A program should be able to run just fine with no options | |
64 | whatsoever. (Pick a random program from the <span class="Unix">Unix</span> or GNU toolsets. Can | |
65 | it run without any options at all and still make sense? The main | |
66 | exceptions are <code>find</code>, <code>tar</code>, and <code>dd</code>--all of which are mutant | |
67 | oddballs that have been rightly criticized for their non-standard syntax | |
68 | and confusing interfaces.) | |
69 | ||
70 | <P> | |
71 | Lots of people want their programs to have ``required options''. Think | |
72 | about it. If it's required, then it's <em>not optional</em>! If there is a | |
73 | piece of information that your program absolutely requires in order to | |
74 | run successfully, that's what positional arguments are for. | |
75 | ||
76 | <P> | |
77 | As an example of good command-line interface design, consider the humble | |
78 | <code>cp</code> utility, for copying files. It doesn't make much sense to try to | |
79 | copy files without supplying a destination and at least one source. | |
80 | Hence, <code>cp</code> fails if you run it with no arguments. However, it has a | |
81 | flexible, useful syntax that does not require any options at all: | |
82 | <div class="verbatim"><pre> | |
83 | cp SOURCE DEST | |
84 | cp SOURCE ... DEST-DIR | |
85 | </pre></div> | |
86 | ||
87 | <P> | |
88 | You can get pretty far with just that. Most <code>cp</code> implementations | |
89 | provide a bunch of options to tweak exactly how the files are copied: | |
90 | you can preserve mode and modification time, avoid following symlinks, | |
91 | ask before clobbering existing files, etc. But none of this distracts | |
92 | from the core mission of <code>cp</code>, which is to copy either one file to | |
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