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[OpenSPARC-T2-DV] / tools / src / nas,5.n2.os.2 / lib / python / html / python / lib / optparse-terminology.html
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55<H3><A NAME="SECTION0082111000000000000000"></A><A NAME="optparse-terminology"></A>
56<BR>
576.21.1.1 Terminology
58</H3>
59<DL>
60<DT><STRONG>argument</STRONG></DT>
61<DD>a string entered on the command-line, and passed by the shell to
62<code>execl()</code> or <code>execv()</code>. In Python, arguments are elements of
63<code>sys.argv[1:]</code> (<code>sys.argv[0]</code> is the name of the program being
64executed). <span class="Unix">Unix</span> shells also use the term ``word''.
65
66<P>
67It is occasionally desirable to substitute an argument list other
68than <code>sys.argv[1:]</code>, so you should read ``argument'' as ``an element of
69<code>sys.argv[1:]</code>, or of some other list provided as a substitute for
70<code>sys.argv[1:]</code>''.
71</DD>
72<DT><STRONG>option </STRONG></DT>
73<DD>an argument used to supply extra information to guide or customize the
74execution of a program. There are many different syntaxes for
75options; the traditional <span class="Unix">Unix</span> syntax is a hyphen (``-'') followed by a
76single letter, e.g. <code>"-x"</code> or <code>"-F"</code>. Also, traditional <span class="Unix">Unix</span>
77syntax allows multiple options to be merged into a single argument,
78e.g. <code>"-x -F"</code> is equivalent to <code>"-xF"</code>. The GNU project
79introduced <code>"-"</code> followed by a series of hyphen-separated words,
80e.g. <code>"-file"</code> or <code>"-dry-run"</code>. These are the only two option
81syntaxes provided by <tt class="module">optparse</tt>.
82
83<P>
84Some other option syntaxes that the world has seen include:
85
86<UL>
87<LI>
88a hyphen followed by a few letters, e.g. <code>"-pf"</code> (this is
89<em>not</em> the same as multiple options merged into a single argument)
90
91<P>
92</LI>
93<LI>
94a hyphen followed by a whole word, e.g. <code>"-file"</code> (this is
95technically equivalent to the previous syntax, but they aren't
96usually seen in the same program)
97
98<P>
99</LI>
100<LI>
101a plus sign followed by a single letter, or a few letters,
102or a word, e.g. <code>"+f"</code>, <code>"+rgb"</code>
103
104<P>
105</LI>
106<LI>
107a slash followed by a letter, or a few letters, or a word, e.g.
108<code>"/f"</code>, <code>"/file"</code>
109
110<P>
111</LI>
112</UL>
113
114<P>
115These option syntaxes are not supported by <tt class="module">optparse</tt>, and they never will
116be. This is deliberate: the first three are non-standard on any
117environment, and the last only makes sense if you're exclusively
118targeting VMS, MS-DOS, and/or Windows.
119</DD>
120<DT><STRONG>option argument</STRONG></DT>
121<DD>an argument that follows an option, is closely associated with that
122option, and is consumed from the argument list when that option is.
123With <tt class="module">optparse</tt>, option arguments may either be in a separate argument
124from their option:
125<div class="verbatim"><pre>
126-f foo
127--file foo
128</pre></div>
129
130<P>
131or included in the same argument:
132<div class="verbatim"><pre>
133-ffoo
134--file=foo
135</pre></div>
136
137<P>
138Typically, a given option either takes an argument or it doesn't.
139Lots of people want an ``optional option arguments'' feature, meaning
140that some options will take an argument if they see it, and won't if
141they don't. This is somewhat controversial, because it makes parsing
142ambiguous: if <code>"-a"</code> takes an optional argument and <code>"-b"</code> is
143another option entirely, how do we interpret <code>"-ab"</code>? Because of
144this ambiguity, <tt class="module">optparse</tt> does not support this feature.
145</DD>
146<DT><STRONG>positional argument</STRONG></DT>
147<DD>something leftover in the argument list after options have been
148parsed, i.e. after options and their arguments have been parsed and
149removed from the argument list.
150</DD>
151<DT><STRONG>required option</STRONG></DT>
152<DD>an option that must be supplied on the command-line; note that the
153phrase ``required option'' is self-contradictory in English. <tt class="module">optparse</tt>
154doesn't prevent you from implementing required options, but doesn't
155give you much help at it either. See <code>examples/required_1.py</code> and
156<code>examples/required_2.py</code> in the <tt class="module">optparse</tt> source distribution for two
157ways to implement required options with <tt class="module">optparse</tt>.
158</DD>
159</DL>
160
161<P>
162For example, consider this hypothetical command-line:
163<div class="verbatim"><pre>
164prog -v --report /tmp/report.txt foo bar
165</pre></div>
166
167<P>
168<code>"-v"</code> and <code>"-report"</code> are both options. Assuming that
169<b class="programopt">--report</b> takes one argument, <code>"/tmp/report.txt"</code> is an option
170argument. <code>"foo"</code> and <code>"bar"</code> are positional arguments.
171
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