211 lines
5.5 KiB
Groff
211 lines
5.5 KiB
Groff
.\" Copyright (c) 1988, 1991 Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)getopt.3 6.16 (Berkeley) 4/19/91
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.\"
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.Dd April 19, 1991
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.Dt GETOPT 3
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.Os BSD 4.3
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.Sh NAME
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.Nm getopt
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.Nd get option letter from argv
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.Sh SYNOPSIS
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.Fd #include <stdlib.h>
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.Vt extern char *optarg
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.Vt extern int optind
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.Vt extern int opterr
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.Ft int
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.Fn getopt "int argc" "char * const *argv" "const char *optstring"
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.Sh DESCRIPTION
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The
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.Fn getopt
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function gets
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the next
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.Em known
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option character from
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.Fa argv .
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An option character is
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.Em known
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if it has been specified in the string of accepted option characters,
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.Fa optstring .
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.Pp
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The option string
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.Fa optstring
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may contain the following characters; letters and
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letters followed by a colon to indicate an option argument
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is to follow. It does not matter to
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.Fn getopt
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if a following argument has leading white space.
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.Pp
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On return from
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.Fn getopt ,
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.Va optarg
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points to an option argument, if it is anticipated,
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and the variable
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.Va optind
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contains the index to the next
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.Fa argv
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argument for a subsequent call
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to
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.Fn getopt .
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.Pp
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The variable
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.Va opterr
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and
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.Va optind
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are both initialized to 1.
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In order to use
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.Fn getopt
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to evaluate multiple sets of arguments, or to evaluate a single set of
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arguments multiple times,
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.Va optind
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must be initialized to the number of argv entries to be skipped in each
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evaluation.
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.Pp
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The
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.Fn getopt
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function
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returns an
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.Dv EOF
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when the argument list is exhausted, or a non-recognized
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option is encountered.
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The interpretation of options in the argument list may be cancelled
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by the option
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.Ql --
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(double dash) which causes
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.Fn getopt
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to signal the end of argument processing and return an
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.Dv EOF .
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When all options have been processed (i.e., up to the first non-option
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argument),
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.Fn getopt
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returns
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.Dv EOF .
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.Sh DIAGNOSTICS
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If the
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.Fn getopt
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function encounters a character not found in the string
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.Va optarg
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or detects
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a missing option argument
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it writes error message
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.Ql ?
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to the
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.Em stderr .
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Setting
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.Va opterr
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to a zero will disable these error messages.
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.Sh EXAMPLE
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.Bd -literal -compact
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extern char *optarg;
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extern int optind;
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int bflag, ch, fd;
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bflag = 0;
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while ((ch = getopt(argc, argv, "bf:")) != EOF)
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switch(ch) {
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case 'b':
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bflag = 1;
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break;
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case 'f':
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if ((fd = open(optarg, O_RDONLY, 0)) < 0) {
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(void)fprintf(stderr,
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"myname: unable to read file %s.\en", optarg);
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exit(1) ;
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}
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break;
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case '?':
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default:
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usage();
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}
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argc -= optind;
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argv += optind;
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.Ed
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.Sh HISTORY
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The
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.Fn getopt
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function appeared
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.Bx 4.3 .
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.Sh BUGS
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Option arguments are allowed to begin with
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.Dq Li \- ;
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this is reasonable but
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reduces the amount of error checking possible.
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.Pp
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A single dash
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.Dq Li -
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may be specified as an character in
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.Fa optstring ,
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however it should
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.Em never
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have an argument associated with it.
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This allows
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.Fn getopt
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to be used with programs that expect
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.Dq Li -
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as an option flag.
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This practice is wrong, and should not be used in any current development.
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It is provided for backward compatibility
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.Em only .
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By default, a single dash causes
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.Fn getopt
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to return
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.Dv EOF .
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This is, we believe, compatible with System V.
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.Pp
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It is also possible to handle digits as option letters.
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This allows
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.Fn getopt
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to be used with programs that expect a number
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.Pq Dq Li \&-\&3
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as an option.
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This practice is wrong, and should not be used in any current development.
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It is provided for backward compatibility
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.Em only .
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The following code fragment works fairly well.
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.Bd -literal -offset indent
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int length;
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char *p;
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while ((c = getopt(argc, argv, "0123456789")) != EOF)
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switch (c) {
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case '0': case '1': case '2': case '3': case '4':
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case '5': case '6': case '7': case '8': case '9':
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p = argv[optind - 1];
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if (p[0] == '-' && p[1] == ch && !p[2])
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length = atoi(++p);
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else
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length = atoi(argv[optind] + 1);
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break;
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}
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}
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.Ed
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