Content-type: text/html Manpage of POPT


Section: Linux Programmer's Manual (3)
Updated: June 30, 1998
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popt - Parse command line options  


#include <popt.h>

poptContext poptGetContext(char * name, int argc,
                           char ** argv,
                           struct poptOption * options,
                           int flags);

void poptFreeContext(poptContext con);

void poptResetContext(poptContext con);

int poptGetNextOpt(poptContext con);

char * poptGetOptArg(poptContext con);

char * poptGetArg(poptContext con);

char * poptPeekArg(poptContext con);

char ** poptGetArgs(poptContext con);

const char * poptStrerror(const int error);

char * poptBadOption(poptContext con, int flags);

int poptReadDefaultConfig(poptContext con, int flags);

int poptReadConfigFile(poptContext con, char * fn);

int poptAddAlias(poptContext con, struct poptAlias alias,
                 int flags);

int poptParseArgvString(char * s, int *  argcPtr,
                        char *** argvPtr);

int poptStuffArgs(poptContext con, char ** argv);



The popt library exists essentially for parsing command-line options. It is found superior in many ways when compared to parsing the argv array by hand or using the getopt functions getopt() and getopt_long() [see getopt(3)]. Some specific advantages of popt are: it does not utilize global variables, thus enabling multiple passes in parsing argv ; it can parse an arbitrary array of argv-style elements, allowing parsing of command-line-strings from any source; it provides a standard method of option aliasing (to be discussed at length below.); it can exec external option filters; and, finally, it can automatically generate help and usage messages for the application.

Like getopt_long(), the popt library supports short and long style options. Recall that a short option consists of a - character followed by a single alphanumeric character. A long option, common in GNU utilities, consists of two - characters followed by a string made up of letters, numbers and hyphens. Long options are optionally allowed to begin with a single -, primarily to allow command-line compatibility between popt applications and X toolkit applications. Either type of option may be followed by an argument. A space separates a short option from its arguments; either a space or an = separates a long option from an argument.

The popt library is highly portable and should work on any POSIX platform. The latest version is always available from:

It may be redistributed under either the GNU General Public License or the GNU Library General Public License, at the distributor's discretion.  




Applications provide popt with information on their command-line options by means of an "option table," i.e., an array of struct poptOption structures:

#include <popt.h>

struct poptOption {
    const char * longName; /* may be NULL */
    char shortName;        /* may be '\0' */
    int argInfo;
    void * arg;            /* depends on argInfo */
    int val;               /* 0 means don't return, just update flag */
    char * descrip;        /* description for autohelp -- may be NULL */
    char * argDescrip;     /* argument description for autohelp */

Each member of the table defines a single option that may be passed to the program. Long and short options are considered a single option that may occur in two different forms. The first two members, longName and shortName, define the names of the option; the first is a long name, while the latter is a single character.

The argInfo member tells popt what type of argument is expected after the argument. If no option is expected, POPT_ARG_NONE should be used. The rest of the valid values are shown in the following table:

If the argInfo value is bitwise or'd with POPT_ARGFLAG_ONEDASH,
the long argument may be given with a single - instead of two. For example,














appropriate type, and an error returned if the conversion fails.
POPT_ARG_VAL causes arg to be set to the (integer) value of
val when the argument is found. This is most often useful for
mutually-exclusive arguments in cases where it is not an error for
multiple arguments to occur and where you want the last argument
specified to win; for example, "rm -i -f". POPT_ARG_VAL causes
the parsing function not to return a value, since the value of val
has already been used.
should return when the option is encountered. If it is 0, the parsing
function does not return a value, instead parsing the next
command-line argument.
if automatic help messages are desired (automatic usage messages can
see below) in the main one which provides the table entries for these
use popt's automatical help, popt displays the appropriate message on
stderr as soon as it finds the option, and exits the program with a
return code of 0. If you want to use popt's automatic help generation in
a different way, you need to explicitly add the option entries to your programs
If the argInfo value is bitwise or'd with POPT_ARGFLAG_DOC_HIDDEN,
the argument will not be shown in help output.
The final structure in the table should have all the pointer values set
end of the table.
There are two types of option table entries which do not specify command
line options. When either of these types of entries are used, the
longName element must be NULL and the shortName element
must be '\0'.
The first of these special entry types allows the application to nest
another option table in the current one; such nesting may extend quite
deeply (the actual depth is limited by the program's stack). Including
other option tables allows a library to provide a standard set of
command-line options to every program which uses it (this is often done
in graphical programming toolkits, for example). To do this, set
the argInfo field to POPT_ARG_INCLUDE_TABLE and the
arg field to point to the table which is being included. If
automatic help generation is being used, the descrip field should
contain a overall description of the option table being included.
The other special option table entry type tells popt to call a function (a
callback) when any option in that table is found. This is especially usefull
when included option tables are being used, as the program which provides
the top-level option table doesn't need to be aware of the other options
which are provided by the included table. When a callback is set for
a table, the parsing function never returns information on an option in
the table. Instead, options information must be retained via the callback
or by having popt set a variable through the option's arg field.
Option callbacks should match the following prototype:
The first parameter is the context which is being parsed (see the next
section for information on contexts), opt points to the option
which triggered this callback, and arg is the option's argument.
If the option does not take an argument, arg is NULL. The
final parameter, data is taken from the descrip field
of the option table entry which defined the callback. As descrip
is a pointer, this allows callback functions to be passed an arbitrary
set of data (though a typecast will have to be used).
The option table entry which defines a callback has an argInfo of
POPT_ARG_CALLBACK, an arg which points to the callback
function, and a descrip field which specifies an arbitrary pointer
to be passed to the callback.
popt can interleave the parsing of multiple command-line sets. It allows
this by keeping all the state information for a particular set of
command-line arguments in a
modified outside the popt library.
The first parameter,
should be the name of the application whose options are being parsed,
two arguments specify the command-line arguments to parse. These are
which was described in the previous section. The final parameter,
0 for compatibility with future versions of the popt library.
parsed and which remain, among other things. If a program wishes to
restart option processing of a set of arguments, it can reset the
When argument processing is complete, the process should free the
context is using.
argument parsing.
Taking the context as its sole argument, this function parses the next
command-line argument found. After finding the next argument in the
option table, the function fills in the object pointed to by the option
non-0, the function then returns that value. Otherwise,
parsed, and other negative values when errors occur. This makes it a
good idea to
pointers, command-line parsing is reduced to the following line of code:
rc = poptGetNextOpt(poptcon);
Many applications require more complex command-line parsing than this,
however, and use the following structure:
while ((rc = poptGetNextOpt(poptcon)) > 0) {

     switch (rc) {

          /* specific arguments are handled here */

When returned options are handled, the application needs to know the
value of any arguments that were specified after the option. There are two
ways to discover them. One is to ask popt to fill in a variable with the
This function returns the argument given for the final option returned by
Many applications take an arbitrary number of command-line arguments,
such as a list of file names. When popt encounters an argument that does
not begin with a -, it assumes it is such an argument and adds it to a list
of leftover arguments. Three functions allow applications to access such
This function returns the next leftover argument and marks it as
The next leftover argument is returned but not marked as processed.
This allows an application to look ahead into the argument list,
without modifying the list.
All the leftover arguments are returned in a manner identical to
The popt library can automatically generate help messages which
describe the options a program accepts. There are two types of help
messages which can be generated. Usage messages are a short messages
which lists valid options, but does not describe them. Help messages
describe each option on one (or more) lines, resulting in a longer, but
more useful, message. Whenever automatic help messages are used, the
descrip and argDescrip fields struct poptOption members
should be filled in for each option.
The POPT_AUTOHELP macro makes it easy to add --usage and
--help messages to your program, and is described in part 1
of this man page. If more control is needed over your help messages,
the following two functions are available:
poptPrintHelp() displays the standard help message to the stdio file
descriptor f, while poptPrintUsage() displays the shorter usage
message. Both functions currently ignore the flags argument; it is
there to allow future changes.
All of the popt functions that can return errors return integers.
When an error occurs, a negative error code is returned. The
following table summarizes the error codes that occur:
Here is a more detailed discussion of each error:
An option that requires an argument was specified on the command
line, but no argument was given. This can be returned only by
A set of option aliases is nested too deeply. Currently, popt
follows options only 10 levels to prevent infinite recursion. Only
A parsed string has a quotation mismatch (such as a single quotation
A conversion from a string to a number (int or long) failed due
to the string containing nonnumeric characters. This occurs when
A string-to-number conversion failed because the number was too
contains the error from the system call. Both
return this error.
Two functions are available to make it easy for applications to provide
good error messages.
This function takes a popt error code and returns a string describing
returned may have been specified through an alias.
These two functions make popt error handling trivial for most
applications. When an error is detected from most of the functions,
an error message is printed along with the error string from
code similiar to the following displays a useful error message:
fprintf(stderr, "%s: %s\n",

        poptBadOption(optCon, POPT_BADOPTION_NOALIAS),

ability to use option aliasing. This lets the user specify options that
popt expands into other options when they are specified. If the standard
information in text files.
an arbitrary number of lines formatted like this:
being defined; currently popt configuration files support only aliases, but
other abilities may be added in the future. The next option is the option
that should be aliased, and it may be either a short or a long option. The
rest of the line specifies the expansion for the alias. It is parsed
similarly to a shell command, which allows \, ", and ' to be used for
quoting. If a backslash is the final character on a line, the next line
in the file is assumed to be a logical continuation of the line containing
the backslash, just as in shell.
as suggested at the beginning of this section.
three functions that define aliases for a context:
configuration file. This allows programs to use program-specific
configuration files.
Occasionally, processes want to specify aliases without having to
read them from a configuration file. This function adds a new alias
currently reserved for future expansion. The new alias is specified
struct poptAlias {

     char * longName; /* may be NULL */

     char shortName; /* may be '\0' */

     int argc;

     char ** argv; /* must be free()able */
define the expansion to use when the aliases option is encountered.
Although popt is usually used for parsing arguments already divided into
are formatted identically to command lines. To facilitate this, popt
provides a function that parses a string into an array of strings,
using rules similiar to normal shell parsing.
of elements parsed, and the pointer pointed to by the final parameter is
set to point to the newly created array. The array is dynamically
with it.
Some applications implement the equivalent of option aliasing but need
allows an application to insert new arguments into the current
"stuffed" arguments are the first to be parsed. popt returns to the
normal arguments once all the stuffed arguments have been exhausted.
The following example is a simplified version of the program "robin"
which appears in Chapter 15 of the text cited below. Robin has
been stripped of everything but its argument-parsing logic, slightly
reworked, and renamed "parse." It may prove useful in illustrating
at least some of the features of the extremely rich popt library.
#include <popt.h>
#include <stdio.h>
void usage(poptContext optCon, int exitcode, char *error, char *addl) {

    poptPrintUsage(optCon, stderr, 0);

    if (error) fprintf(stderr, "%s: %s, error, addl);

int main(int argc, char *argv[]) {

   char    c;            /* used for argument parsing */

   int     i = 0;        /* used for tracking options */

   char    *portname;

   int     speed = 0;    /* used in argument parsing to set speed */

   int     raw = 0;      /* raw mode? */ 

   int     j;

   char    buf[BUFSIZ+1];

   poptContext optCon;   /* context for parsing command-line options */

   struct poptOption optionsTable[] = {


   optCon = poptGetContext(NULL, argc, argv, optionsTable, 0);

   poptSetOtherOptionHelp(optCon, "[OPTIONS]* <port>");

   if (argc < 2) {


   /* Now do options processing, get portname */

   while ((c = poptGetNextOpt(optCon)) >= 0) {

      switch (c) {

         case 'c': 

            buf[i++] = 'c';         


         case 'h': 

            buf[i++] = 'h';


         case 's':

            buf[i++] = 's';


         case 'n':

            buf[i++] = 'n';




   portname = poptGetArg(optCon);

   if((portname == NULL) || !(poptPeekArg(optCon) == NULL))

      usage(optCon, 1, "Specify a single port", ".e.g., /dev/cua0");

   if (c < -1) {

      /* an error occurred during option processing */

      fprintf(stderr, "%s: %s\n", 

              poptBadOption(optCon, POPT_BADOPTION_NOALIAS),


      return 1;


   /* Print out options, portname chosen */

   printf("Options  chosen: ");

   for(j = 0; j < i ; j++)

      printf("-%c ", buf[j]);

   if(raw) printf("-r ");

   if(speed) printf("-b %d ", speed);

   printf("\nPortname chosen: %s\n", portname);


RPM, a popular Linux package management program, makes heavy use
of popt's features. Many of its command-line arguments are implemented
through popt aliases, which makes RPM an excellent example of how to
take advantage of the popt library. For more information on RPM, see The popt source code distribution includes test
program(s) which use all of the features of the popt libraries in
various ways. If a feature isn't working for you, the popt test code
is the first place to look.
None presently known.
Erik W. Troan <>
This man page is derived in part from
by Michael K. Johnson and Erik W. Troan, Copyright (c) 1998 by Addison
Wesley Longman, Inc., and included in the popt documentation with the
permission of the Publisher and the appreciation of the Authors.
Thanks to Robert Lynch for his extensive work on this man page.
Erik W. Troan (Addison-Wesley, 1998; ISBN 0-201-30821-5), Chapter 24.
chapter. It can be found in the source archive for popt available at:




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