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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 | |
| 93 | another, or several files to another directory. | |
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