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GETOPT(3P) POSIX Programmer's Manual GETOPT(3P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
getopt, optarg, opterr, optind, optopt — command option parsing
#include <unistd.h>
int getopt(int argc, char * const argv[], const char *optstring);
extern char *optarg;
extern int opterr, optind, optopt;
The getopt() function is a command-line parser that shall follow
Utility Syntax Guidelines 3, 4, 5, 6, 7, 9, and 10 in the Base
Definitions volume of POSIX.1‐2008, Section 12.2, Utility Syntax
Guidelines.
The parameters argc and argv are the argument count and argument
array as passed to main() (see exec()). The argument optstring is a
string of recognized option characters; if a character is followed by
a <colon>, the option takes an argument. All option characters
allowed by Utility Syntax Guideline 3 are allowed in optstring. The
implementation may accept other characters as an extension.
The variable optind is the index of the next element of the argv[]
vector to be processed. It shall be initialized to 1 by the system,
and getopt() shall update it when it finishes with each element of
argv[]. If the application sets optind to zero before calling
getopt(), the behavior is unspecified. When an element of argv[]
contains multiple option characters, it is unspecified how getopt()
determines which options have already been processed.
The getopt() function shall return the next option character (if one
is found) from argv that matches a character in optstring, if there
is one that matches. If the option takes an argument, getopt() shall
set the variable optarg to point to the option-argument as follows:
1. If the option was the last character in the string pointed to by
an element of argv, then optarg shall contain the next element of
argv, and optind shall be incremented by 2. If the resulting
value of optind is greater than argc, this indicates a missing
option-argument, and getopt() shall return an error indication.
2. Otherwise, optarg shall point to the string following the option
character in that element of argv, and optind shall be
incremented by 1.
If, when getopt() is called:
argv[optind] is a null pointer
*argv[optind] is not the character −
argv[optind] points to the string "−"
getopt() shall return −1 without changing optind. If:
argv[optind] points to the string "−−"
getopt() shall return −1 after incrementing optind.
If getopt() encounters an option character that is not contained in
optstring, it shall return the <question-mark> ('?') character. If
it detects a missing option-argument, it shall return the <colon>
character (':') if the first character of optstring was a <colon>, or
a <question-mark> character ('?') otherwise. In either case,
getopt() shall set the variable optopt to the option character that
caused the error. If the application has not set the variable opterr
to 0 and the first character of optstring is not a <colon>, getopt()
shall also print a diagnostic message to stderr in the format
specified for the getopts utility.
The getopt() function need not be thread-safe.
The getopt() function shall return the next option character
specified on the command line.
A <colon> (':') shall be returned if getopt() detects a missing
argument and the first character of optstring was a <colon> (':').
A <question-mark> ('?') shall be returned if getopt() encounters an
option character not in optstring or detects a missing argument and
the first character of optstring was not a <colon> (':').
Otherwise, getopt() shall return −1 when all command line options are
parsed.
If the application has not set the variable opterr to 0, the first
character of optstring is not a <colon>, and a write error occurs
while getopt() is printing a diagnostic message to stderr, then the
error indicator for stderr shall be set; but getopt() shall still
succeed and the value of errno after getopt() is unspecified.
The following sections are informative.
Parsing Command Line Options
The following code fragment shows how you might process the arguments
for a utility that can take the mutually-exclusive options a and b
and the options f and o, both of which require arguments:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int
main(int argc, char *argv[ ])
{
int c;
int bflg = 0, aflg = 0, errflg = 0;
char *ifile;
char *ofile;
. . .
while ((c = getopt(argc, argv, ":abf:o:")) != -1) {
switch(c) {
case 'a':
if (bflg)
errflg++;
else
aflg++;
break;
case 'b':
if (aflg)
errflg++;
else
bflg++;
break;
case 'f':
ifile = optarg;
break;
case 'o':
ofile = optarg;
break;
case ':': /* -f or -o without operand */
fprintf(stderr,
"Option -%c requires an operand\n", optopt);
errflg++;
break;
case '?':
fprintf(stderr,
"Unrecognized option: '-%c'\n", optopt);
errflg++;
}
}
if (errflg) {
fprintf(stderr, "usage: . . . ");
exit(2);
}
for ( ; optind < argc; optind++) {
if (access(argv[optind], R_OK)) {
. . .
}
This code accepts any of the following as equivalent:
cmd −ao arg path path
cmd −a −o arg path path
cmd −o arg −a path path
cmd −a −o arg −− path path
cmd −a −oarg path path
cmd −aoarg path path
Selecting Options from the Command Line
The following example selects the type of database routines the user
wants to use based on the Options argument.
#include <unistd.h>
#include <string.h>
...
const char *Options = "hdbtl";
...
int dbtype, c;
char *st;
...
dbtype = 0;
while ((c = getopt(argc, argv, Options)) != −1) {
if ((st = strchr(Options, c)) != NULL) {
dbtype = st - Options;
break;
}
}
The getopt() function is only required to support option characters
included in Utility Syntax Guideline 3. Many historical
implementations of getopt() support other characters as options. This
is an allowed extension, but applications that use extensions are not
maximally portable. Note that support for multi-byte option
characters is only possible when such characters can be represented
as type int.
While ferror(stderr) may be used to detect failures to write a
diagnostic to stderr when getopt() returns '?', the value of errno is
unspecified in such a condition. Applications desiring more control
over handling write failures should set opterr to 0 and independently
perform output to stderr, rather than relying on getopt() to do the
output.
The optopt variable represents historical practice and allows the
application to obtain the identity of the invalid option.
The description has been written to make it clear that getopt(), like
the getopts utility, deals with option-arguments whether separated
from the option by <blank> characters or not. Note that the
requirements on getopt() and getopts are more stringent than the
Utility Syntax Guidelines.
The getopt() function shall return −1, rather than EOF, so that
<stdio.h> is not required.
The special significance of a <colon> as the first character of
optstring makes getopt() consistent with the getopts utility. It
allows an application to make a distinction between a missing
argument and an incorrect option letter without having to examine the
option letter. It is true that a missing argument can only be
detected in one case, but that is a case that has to be considered.
None.
exec(1p)
The Base Definitions volume of POSIX.1‐2008, Section 12.2, Utility
Syntax Guidelines, unistd.h(0p)
The Shell and Utilities volume of POSIX.1‐2008, getopts(1p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 GETOPT(3P)
Pages that refer to this page: stdio.h(0p), unistd.h(0p), getopts(1p), getsubopt(3p), optarg(3p)