151 lines
2.8 KiB
Groff
151 lines
2.8 KiB
Groff
.\" Copyright (c) 1985 Regents of the University of California.
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.\" All rights reserved. The Berkeley software License Agreement
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.\" specifies the terms and conditions for redistribution.
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.\"
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.\" @(#)getopt.3 6.4 (Berkeley) 5/27/86
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.\"
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.TH GETOPT 3 "May 27, 1986"
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.UC 6
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.SH NAME
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getopt \- get option letter from argv
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.SH SYNOPSIS
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.ft B
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int getopt(argc, argv, optstring)
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.br
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int argc;
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.br
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char **argv;
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.br
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char *optstring;
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.sp
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extern char *optarg;
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.br
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extern int optind;
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.ft
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.SH DESCRIPTION
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.I Getopt
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returns the next option letter in
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.I argv
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that matches a letter in
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.IR optstring .
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.I Optstring
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is a string of recognized option letters;
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if a letter is followed by a colon, the option is expected to have
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an argument that may or may not be separated from it by white space.
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.I Optarg
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is set to point to the start of the option argument on return from
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.IR getopt .
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.PP
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.I Getopt
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places in
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.I optind
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the
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.I argv
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index of the next argument to be processed.
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Because
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.I optind
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is external, it is normally initialized to zero automatically
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before the first call to
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.IR getopt .
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.PP
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When all options have been processed (i.e., up to the first
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non-option argument),
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.I getopt
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returns
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.BR EOF .
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The special option
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.B \-\-
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may be used to delimit the end of the options;
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.B EOF
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will be returned, and
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.B \-\-
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will be skipped.
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.SH DIAGNOSTICS
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.I Getopt
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prints an error message on
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.I stderr
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and returns a question mark
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.RB ( ? )
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when it encounters an option letter not included in
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.IR optstring .
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.SH EXAMPLE
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The following code fragment shows how one might process the arguments
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for a command that can take the mutually exclusive options
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.B a
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and
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.BR b ,
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and the options
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.B f
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and
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.BR o ,
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both of which require arguments:
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.PP
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.RS
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.nf
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main(argc, argv)
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int argc;
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char **argv;
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{
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int c;
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extern int optind;
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extern char *optarg;
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\&.
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\&.
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\&.
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while ((c = getopt(argc, argv, "abf:o:")) != EOF)
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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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bproc();
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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 `?':
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default:
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errflg++;
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break;
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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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\&.
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\&.
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\&.
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}
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\&.
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\&.
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\&.
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}
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.RE
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.SH HISTORY
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Written by Henry Spencer, working from a Bell Labs manual page.
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Modified by Keith Bostic to behave more like the System V version.
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.SH BUGS
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It is not obvious how
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`\-'
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standing alone should be treated; this version treats it as
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a non-option argument, which is not always right.
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.PP
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Option arguments are allowed to begin with `\-';
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this is reasonable but reduces the amount of error checking possible.
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.PP
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.I Getopt
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is quite flexible but the obvious price must be paid: there is much
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it could do that it doesn't, like
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checking mutually exclusive options, checking type of
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option arguments, etc.
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