337 lines
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337 lines
12 KiB
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<title>getopt</title>
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<body bgcolor="white">
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<basefont size="3"> <a name="getopt"></a> <a name="tag_03_234"></a><!-- getopt -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_234_01"></a>NAME</h4>
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<blockquote>getopt, optarg, opterr, optind, optopt - command option parsing</blockquote>
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<h4><a name="tag_03_234_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/unistd.h.html">unistd.h</a>><br>
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<br>
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int getopt(int</tt> <i>argc</i><tt>, char * const</tt> <i>argv</i><tt>[], const char *</tt><i>optstring</i><tt>);<br>
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extern char *optarg;<br>
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extern int optind, opterr, optopt;<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_234_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>getopt</i>() function is a command-line parser that shall follow Utility Syntax Guidelines 3, 4, 5, 6, 7, 9, and 10 in
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the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap12.html#tag_12_02">Section 12.2,
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Utility Syntax Guidelines</a>.</p>
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<p>The parameters <i>argc</i> and <i>argv</i> are the argument count and argument array as passed to <i>main</i>() (see <a href=
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"exec.html"><i><a href="../functions/exec.html">exec</a></i>()</a> ). The argument <i>optstring</i> is a string of recognized
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option characters; if a character is followed by a colon, the option takes an argument. All option characters allowed by Utility
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Syntax Guideline 3 are allowed in <i>optstring</i>. The implementation may accept other characters as an extension.</p>
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<p>The variable <i>optind</i> is the index of the next element of the <i>argv</i>[] vector to be processed. It shall be initialized
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to 1 by the system, and <i>getopt</i>() shall update it when it finishes with each element of <i>argv</i>[]. When an element of
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<i>argv</i>[] contains multiple option characters, it is unspecified how <i>getopt</i>() determines which options have already been
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processed.</p>
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<p>The <i>getopt</i>() function shall return the next option character (if one is found) from <i>argv</i> that matches a character
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in <i>optstring</i>, if there is one that matches. If the option takes an argument, <i>getopt</i>() shall set the variable
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<i>optarg</i> to point to the option-argument as follows:</p>
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<ol>
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<li>
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<p>If the option was the last character in the string pointed to by an element of <i>argv</i>, then <i>optarg</i> shall contain the
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next element of <i>argv</i>, and <i>optind</i> shall be incremented by 2. If the resulting value of <i>optind</i> is greater than
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<i>argc</i>, this indicates a missing option-argument, and <i>getopt</i>() shall return an error indication.</p>
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</li>
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<li>
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<p>Otherwise, <i>optarg</i> shall point to the string following the option character in that element of <i>argv</i>, and
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<i>optind</i> shall be incremented by 1.</p>
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</li>
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</ol>
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<p>If, when <i>getopt</i>() is called:</p>
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<pre>
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<i>argv</i><tt>[optind]</tt> is a null pointer<tt>*</tt>
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<i>argv</i><tt>[optind]</tt> is not the character <tt>- </tt>
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<i>argv</i><tt>[optind]</tt> points to the string <tt>"-"</tt>
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</pre>
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<p><i>getopt</i>() shall return -1 without changing <i>optind</i>. If:</p>
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<pre>
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<i>argv</i><tt>[optind] </tt> points to the string <tt>"--"
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</tt>
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</pre>
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<p><i>getopt</i>() shall return -1 after incrementing <i>optind</i>.</p>
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<p>If <i>getopt</i>() encounters an option character that is not contained in <i>optstring</i>, it shall return the question-mark (
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<tt>'?'</tt> ) character. If it detects a missing option-argument, it shall return the colon character ( <tt>':'</tt> ) if the
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first character of <i>optstring</i> was a colon, or a question-mark character ( <tt>'?'</tt> ) otherwise. In either case,
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<i>getopt</i>() shall set the variable <i>optopt</i> to the option character that caused the error. If the application has not set
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the variable <i>opterr</i> to 0 and the first character of <i>optstring</i> is not a colon, <i>getopt</i>() shall also print a
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diagnostic message to <i>stderr</i> in the format specified for the <a href="../utilities/getopts.html"><i>getopts</i></a>
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utility.</p>
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<p>The <i>getopt</i>() function need not be reentrant. A function that is not required to be reentrant is not required to be
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thread-safe.</p>
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</blockquote>
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<h4><a name="tag_03_234_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>The <i>getopt</i>() function shall return the next option character specified on the command line.</p>
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<p>A colon ( <tt>':'</tt> ) shall be returned if <i>getopt</i>() detects a missing argument and the first character of
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<i>optstring</i> was a colon ( <tt>':'</tt> ).</p>
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<p>A question mark ( <tt>'?'</tt> ) shall be returned if <i>getopt</i>() encounters an option character not in <i>optstring</i> or
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detects a missing argument and the first character of <i>optstring</i> was not a colon ( <tt>':'</tt> ).</p>
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<p>Otherwise, <i>getopt</i>() shall return -1 when all command line options are parsed.</p>
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</blockquote>
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<h4><a name="tag_03_234_05"></a>ERRORS</h4>
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<blockquote>
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<p>No errors are defined.</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_234_06"></a>EXAMPLES</h4>
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<blockquote>
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<h5><a name="tag_03_234_06_01"></a>Parsing Command Line Options</h5>
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<p>The following code fragment shows how you might process the arguments for a utility that can take the mutually-exclusive options
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<i>a</i> and <i>b</i> and the options <i>f</i> and <i>o</i>, both of which require arguments:</p>
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<pre>
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<tt>#include <unistd.h>
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<br>
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int
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main(int argc, char *argv[ ])
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{
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int c;
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int bflg, aflg, errflg;
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char *ifile;
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char *ofile;
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extern char *optarg;
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extern int optind, optopt;
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. . .
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while ((c = getopt(argc, argv, ":abf:o:")) != -1) {
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switch(c) {
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case 'a':
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if (bflg)
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errflg++;
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else
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aflg++;
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break;
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case 'b':
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if (aflg)
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errflg++;
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else {
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bflg++;
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bproc();
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}
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break;
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case 'f':
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ifile = optarg;
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break;
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case 'o':
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ofile = optarg;
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break;
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case ':': /* -f or -o without operand */
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fprintf(stderr,
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"Option -%c requires an operand\n", optopt);
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errflg++;
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break;
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case '?':
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fprintf(stderr,
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"Unrecognized option: -%c\n", optopt);
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errflg++;
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}
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}
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if (errflg) {
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fprintf(stderr, "usage: . . . ");
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exit(2);
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}
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for ( ; optind < argc; optind++) {
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if (access(argv[optind], R_OK)) {
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. . .
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}
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</tt>
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</pre>
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<p>This code accepts any of the following as equivalent:</p>
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<pre>
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<tt>cmd -ao arg path path
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cmd -a -o arg path path
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cmd -o arg -a path path
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cmd -a -o arg -- path path
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cmd -a -oarg path path
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cmd -aoarg path path
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</tt>
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</pre>
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<h5><a name="tag_03_234_06_02"></a>Checking Options and Arguments</h5>
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<p>The following example parses a set of command line options and prints messages to standard output for each option and argument
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that it encounters.</p>
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<pre>
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<tt>#include <unistd.h>
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#include <stdio.h>
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...
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int c;
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char *filename;
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extern char *optarg;
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extern int optind, optopt, opterr;
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...
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while ((c = getopt(argc, argv, ":abf:")) != -1) {
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switch(c) {
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case 'a':
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printf("a is set\n");
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break;
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case 'b':
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printf("b is set\n");
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break;
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case 'f':
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filename = optarg;
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printf("filename is %s\n", filename);
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break;
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case ':':
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printf("-%c without filename\n", optopt);
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break;
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case '?':
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printf("unknown arg %c\n", optopt);
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break;
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}
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}
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</tt>
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</pre>
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<h5><a name="tag_03_234_06_03"></a>Selecting Options from the Command Line</h5>
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<p>The following example selects the type of database routines the user wants to use based on the <i>Options</i> argument.</p>
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<pre>
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<tt>#include <unistd.h>
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#include <string.h>
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...
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char *Options = "hdbtl";
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...
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int dbtype, i;
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char c;
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char *st;
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...
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dbtype = 0;
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while ((c = getopt(argc, argv, Options)) != -1) {
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if ((st = strchr(Options, c)) != NULL) {
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dbtype = st - Options;
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break;
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}
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}
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_234_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <i>getopt</i>() function is only required to support option characters included in Utility Syntax Guideline 3. Many
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historical implementations of <i>getopt</i>() support other characters as options. This is an allowed extension, but applications
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that use extensions are not maximally portable. Note that support for multi-byte option characters is only possible when such
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characters can be represented as type <b>int</b>.</p>
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</blockquote>
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<h4><a name="tag_03_234_08"></a>RATIONALE</h4>
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<blockquote>
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<p>The <i>optopt</i> variable represents historical practice and allows the application to obtain the identity of the invalid
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option.</p>
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<p>The description has been written to make it clear that <i>getopt</i>(), like the <a href=
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"../utilities/getopts.html"><i>getopts</i></a> utility, deals with option-arguments whether separated from the option by
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<blank>s or not. Note that the requirements on <i>getopt</i>() and <a href="../utilities/getopts.html"><i>getopts</i></a> are
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more stringent than the Utility Syntax Guidelines.</p>
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<p>The <i>getopt</i>() function shall return -1, rather than EOF, so that <a href=
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"../basedefs/stdio.h.html"><i><stdio.h></i></a> is not required.</p>
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<p>The special significance of a colon as the first character of <i>optstring</i> makes <i>getopt</i>() consistent with the <a
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href="../utilities/getopts.html"><i>getopts</i></a> utility. It allows an application to make a distinction between a missing
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argument and an incorrect option letter without having to examine the option letter. It is true that a missing argument can only be
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detected in one case, but that is a case that has to be considered.</p>
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</blockquote>
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<h4><a name="tag_03_234_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_234_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="exec.html"><i><a href="../functions/exec.html">exec</a></i>()</a> , the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../basedefs/unistd.h.html"><i><unistd.h></i></a>, the Shell and Utilities volume of
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IEEE Std 1003.1-2001</p>
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</blockquote>
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<h4><a name="tag_03_234_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_234_12"></a>Issue 5</h4>
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<blockquote>
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<p>A note indicating that the <i>getopt</i>() function need not be reentrant is added to the DESCRIPTION.</p>
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</blockquote>
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<h4><a name="tag_03_234_13"></a>Issue 6</h4>
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<blockquote>
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<p>IEEE PASC Interpretation 1003.2 #150 is applied.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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