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<refentry id="libpopt-3">

<refmeta><refentrytitle>&cmd;</refentrytitle><manvolnum>3</manvolnum>

<refmiscinfo class="date">31 May 2004</refmiscinfo>

<refmiscinfo class="sectdesc">&man3;</refmiscinfo>

<refmiscinfo class="software">&release;</refmiscinfo>

<refmiscinfo class="arch">generic</refmiscinfo>

<refmiscinfo class="copyright">&suncopy;</refmiscinfo>

</refmeta>

<indexterm><primary>&cmd;</primary></indexterm><indexterm><primary>parse

command-line options</primary></indexterm>

<refnamediv id="libpopt-3-name"><refname>&cmd;</refname><refpurpose>parse

command-line options</refpurpose></refnamediv>

<refsect1 id="libpopt-3-synp"><title>&synp-tt;</title>

<programlisting>#include &lt;popt.h>

poptContext poptGetContext(const char * name, int argc,

const char ** argv,

const struct poptOption * options,

int flags);

void poptFreeContext(poptContext con);

void poptResetContext(poptContext con);

int poptGetNextOpt(poptContext con);

const char * poptGetOptArg(poptContext con);

const char * poptGetArg(poptContext con);

const char * poptPeekArg(poptContext con);

const char ** poptGetArgs(poptContext con);

const char *const poptStrerror(const int error);

const 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,

const char *** argvPtr);

int poptDupArgv(int argc, const char ** argv, int * argcPtr,

const char *** argvPtr);

int poptStuffArgs(poptContext con, const char ** argv);</programlisting>

</refsect1>

<refsect1 id="libpopt-3-desc"><title>&desc-tt;</title>

<para>The <filename>popt</filename> library parses command-line options. The <filename>

popt</filename> library provides an alternative to parsing the <literal>argv

</literal> array by hand, or using the <citerefentry><refentrytitle>getopt

</refentrytitle><manvolnum>3</manvolnum></citerefentry> functions <literal>

getopt()</literal> and <literal>getopt_long()</literal>. </para>

<para>The <filename>popt</filename> library has the following advantages:

</para>

<itemizedlist>

<listitem><para><filename>popt</filename> does not use global variables, thus

enabling multiple passes in parsing <literal>argv</literal>.</para></listitem>

<listitem><para><filename>popt</filename> can parse an arbitrary array of <literal>

argv</literal>-style elements, allowing parsing of command-line strings from

any source.</para></listitem>

<listitem><para><filename>popt</filename> provides a standard method of option

aliasing. This feature is discussed in detail below.</para></listitem>

<listitem><para><filename>popt</filename> can exec external option filters.

</para></listitem>

<listitem><para><filename>popt</filename> can automatically generate help

and usage messages for the application.</para></listitem>

</itemizedlist>

<para>The <filename>popt</filename> library supports short and long options.

A short option consists of a hyphen followed by a single alphanumeric character.

A long option, common in GNU utilities, consists of two hyphens followed by

a string composed of letters, numbers, and hyphens. Long options can optionally

begin with a single hyphen, primarily to allow command-line compatibility

between <filename>popt</filename> applications and X toolkit applications.

Either type of option can be followed by an argument. A space separates a

short option from its argument. Either a space or an equals sign separates

a long option from an argument.</para>

<para>The <filename>popt</filename> library is highly portable and should

work on any POSIX platform. The latest version is distributed with <literal>

rpm</literal> and is available from: <filename>ftp://ftp.rpm.org/pub/rpm/dist

</filename>.</para>

<para>The <filename>popt</filename> library may be redistributed under the

X consortium license, see the file <filename>COPYING</filename> in the <filename>

popt</filename> source distribution for details.</para>

</refsect1>

<refsect1 id="libpopt-3-exde"><title>&exde-tt;</title>

<refsect2 id="libpopt-3-exde-optb">

<title>Option Tables</title>

<para>Each application provides <filename>popt</filename> with information

about the command-line options for the application, by means of an option

table. An option table is an array of <literal>struct poptOption</literal>

structures, with the following format:</para>

<programlisting>#include &lt;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 do not return, just update flag */

char * descrip; /* description for autohelp -- may be NULL */

char * argDescrip; /* argument description for autohelp */

};</programlisting>

<refsect3 id="libpopt-3-exde-optb-memb">

<title>Option Table Members</title>

<para>Each member of the table defines a single option that may be passed

to the program. Long and short options are considered to be a single option

that can occur in two different forms. The option table members are as follows:

</para>

<variablelist termlength="medium">

<varlistentry><term><literal>longName</literal></term><listitem><para>Defines

the name of the option in a long name.</para>

</listitem></varlistentry>

<varlistentry><term><literal>shortName</literal></term><listitem><para>Defines

the name of the option in a single character.</para>

</listitem></varlistentry>

<varlistentry><term><literal>argInfo</literal></term><listitem><para>Tells <filename>

popt</filename> what type of argument is expected after the option. Valid

values are as follows: </para>

<variablelist termlength="narrow">

<varlistentry><term>POPT_ARG_DOUBLE</term><listitem><para>Double argument

expected, <literal>arg</literal> type: <literal>double</literal></para>

</listitem></varlistentry>

<varlistentry><term>POPT_ARG_FLOAT</term><listitem><para>Float argument expected, <literal>

arg</literal> type: <literal>float</literal></para>

</listitem></varlistentry>

<varlistentry><term>POPT_ARG_INT</term><listitem><para>Integer argument expected, <literal>

arg</literal> type: <literal>int</literal></para>

</listitem></varlistentry>

<varlistentry><term>POPT_ARG_LONG</term><listitem><para>Long integer expected, <literal>

arg</literal> type: <literal>long</literal></para>

</listitem></varlistentry>

<varlistentry><term>POPT_ARG_NONE</term><listitem><para>No argument expected, <literal>

arg</literal> type: <literal>int</literal></para>

</listitem></varlistentry>

<varlistentry><term>POPT_ARG_STRING</term><listitem><para>No type checking

to be performed, <literal>arg</literal> type: <literal>char *</literal></para>

</listitem></varlistentry>

<varlistentry><term>POPT_ARG_VAL</term><listitem><para>Integer value taken

from val, <literal>arg</literal> type: <literal>int</literal></para>

</listitem></varlistentry>

</variablelist><para>For numeric values, if the <literal>argInfo</literal>

value is bitwise or'd with one of POPT_ARGFLAG_OR, POPT_ARGFLAG_AND, or POPT_ARGFLAG_XOR,

the value is saved by performing an OR, AND, or XOR. If the <literal>argInfo

</literal> value is bitwise or'd with POPT_ARGFLAG_NOT, the value is negated

before saving. For the common operations of setting or clearing bits, POPT_BIT_SET

and POPT_BIT_CLR have the appropriate flags set to perform bit operations.

</para>

<para>If the <literal>argInfo</literal>value is bitwise or'd with POPT_ARGFLAG_ONEDASH,

the long argument may be given with a single hyphen instead of two. For example,

if <option>&ndash;longopt</option> is an option with POPT_ARGFLAG_ONEDASH, <option>

longopt</option> is also accepted.</para>

</listitem></varlistentry>

<varlistentry><term><literal>arg</literal></term><listitem><para>Allows <filename>

popt</filename> to automatically update program variables. If <literal>arg

</literal> is NULL, <filename>popt</filename> ignores <literal>arg</literal>

and takes no special action. Otherwise, <literal>arg</literal> points to a

variable of the appropriate type, as follows: <itemizedlist>

<listitem><para>If <literal>argInfo</literal> is POPT_ARG_NONE, the variable

pointed to by <literal>arg</literal> is set to 1 when the option is used.

</para>

</listitem>

<listitem><para>If the option takes an argument, the variable pointed to by <literal>

arg</literal> is updated to reflect the value of the argument. Any string

is acceptable for POPT_ARG_STRING arguments. POPT_ARG_INT, POPT_ARG_LONG,

POPT_ARG_FLOAT, and POPT_ARG_DOUBLE arguments are converted to the appropriate

type, and an error returned if the conversion fails.</para>

</listitem>

</itemizedlist></para>

<para>POPT_ARG_VAL causes <literal>arg</literal> to be set to the integer

value of <literal>val</literal> when the argument is found. This is 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 take

precedence, for example, <command>rm -i -f</command>. POPT_ARG_VAL causes

the parsing function not to return a value, because the value of <literal>

val</literal> has already been used.</para>

<para>If the <literal>argInfo</literal> value is bitwise or'd with POPT_ARGFLAG_OPTIONAL,

the argument to the long option may be omitted. If the long option is used

without an argument, a default value of zero or NULL is saved if the <literal>

arg</literal> pointer is present. Otherwise, the behavior is identical to

that of a long option with an argument.</para>

</listitem></varlistentry>

<varlistentry><term><literal>val</literal></term><listitem><para>The value

returned by the <filename>popt</filename> parsing function when the option

is encountered. If <literal>val</literal> is 0, the parsing function does

not return a value. Instead, <filename>popt</filename> parses the next command-line

argument.</para>

</listitem></varlistentry>

<varlistentry><term>descrip</term><listitem><para>Text description of the

argument. Only required if automatic help messages are desired. Automatic

usage messages can be generated without this argument.</para>

</listitem></varlistentry>

<varlistentry><term>argDescrip</term><listitem><para>Short summary of the

type of arguments expected by the option, or NULL if the option does not require

any arguments. Only required if automatic help messages are desired. Automatic

usage messages can be generated without this argument.</para>

</listitem></varlistentry>

</variablelist><para>The final structure in the table should have all pointer

values set to NULL and all arithmetic values set to 0, marking the end of

the table. The macro POPT_TABLEEND performs these tasks.</para>

</refsect3>

<refsect3 id="libpopt-3-exde-optb-huse">

<title>Help and Usage Output</title>

<para>If <filename>popt</filename> should automatically provide <option>&minus;usage

</option> and <option>&minus;help</option> options, one line in the option

table should contain the macro POPT_AUTOHELP. This macro includes another

option table, via POPT_ARG_INCLUDE_TABLE, which provides the table entries

for these arguments. When the <option>&minus;usage</option> or <option>&minus;help

</option> option is passed to applications that use <filename>popt</filename>

automatic help, <filename>popt</filename> displays the appropriate message

on <literal>stderr</literal>, and exits the application with a return code

of 0. To use <filename>popt</filename> automatic help generation in a different

way, you must explicitly add the option entries to the application's option

table, instead of using POPT_AUTOHELP.</para>

<para>If the <literal>argInfo</literal> value is bitwise or'd with POPT_ARGFLAG_DOC_HIDDEN,

the argument is not shown in help output.</para>

<para>If the <literal>argInfo</literal> value is bitwise or'd with POPT_ARGFLAG_SHOW_DEFAULT,

the inital value of the <literal>arg</literal> is shown in help output.</para>

</refsect3>

<refsect3 id="libpopt-3-exde-optb-spec">

<title>Special Option Table Entries</title>

<para>Two types of option table entries do not specify command-line options.

When either of these types of entries is used, the <literal>longName</literal>

element must be NULL and the <literal>shortName</literal> element must be <literal>

\\0</literal>.</para>

<para>The first of these special entry types allows the application to nest

another option table in the current option table. Such nesting may extend

quite deeply, the actual depth is limited by the application stack. Including

other option tables allows a library to provide a standard set of command-line

options to every application that uses the library. This is often done in

graphical programming toolkits, for example. To nest another option table,

set the <literal>argInfo</literal> field to POPT_ARG_INCLUDE_TABLE and the <literal>

arg</literal> field to point to the table that is being included. If automatic

help generation is used, the <literal>descrip</literal> field should contain

an overall description of the option table being included.</para>

<para>The other special option table entry type tells <filename>popt</filename>

to call a function when any option in that table is found. This callback functionality

is especially useful when included option tables are used, because the application

that provides the top-level option table does not need to be aware of the

other options that 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, option information must be retained via the callback

or by having <filename>popt</filename> set a variable through the option's <literal>

arg</literal> field. Option callbacks should match the following prototype:

</para>

<literallayout>void poptCallbackType(poptContext con,

const struct poptOption * opt,

const char * arg, void * data);

</literallayout>

<para>The callback uses the following parameters:</para>

<variablelist termlength="narrow">

<varlistentry><term><literal>con</literal></term><listitem><para>The context

that is being parsed. See the next section for information on contexts.</para>

</listitem></varlistentry>

<varlistentry><term><literal>opt</literal></term><listitem><para>The option

that triggered this callback.</para>

</listitem></varlistentry>

<varlistentry><term><literal>arg</literal></term><listitem><para>The argument

for the <literal>opt</literal> option. If the option does not take an argument, <literal>

arg</literal> is NULL.</para>

</listitem></varlistentry>

<varlistentry><term><literal>data</literal></term><listitem><para>Taken from

the <literal>descrip</literal> field of the option table entry that defined

the callback. As <literal>descrip</literal> is a pointer, this allows you

to pass an arbitrary set of data to callback functions, though a typecast

must be used.</para>

</listitem></varlistentry>

</variablelist><para>The option table entry that defines a callback has an <literal>

argInfo</literal> of POPT_ARG_CALLBACK, an <literal>arg</literal> that points

to the callback function, and a <literal>descrip</literal> field that specifies

an arbitrary pointer to be passed to the callback.</para>

</refsect3>

</refsect2>

<refsect2 id="libpopt-3-exde-ctxt">

<title>Creating a Context</title>

<para><filename>popt</filename> can interleave the parsing of multiple command-line

sets. <filename>popt</filename> allows this by keeping all of the state information

for a particular set of command-line arguments in a <literal>poptContext</literal>

data structure, an opaque type that should not be modified outside the <filename>

popt</filename> library.</para>

<para>New <filename>popt</filename> contexts are created by <literal>poptGetContext()

</literal>:</para>

<programlisting>poptContext poptGetContext(const char * name, int argc,

const char ** argv,

const struct poptOption * options,

int flags);</programlisting>

<para>The <literal>poptGetContext()</literal> function takes the following

parameters:</para>

<variablelist>

<varlistentry><term><filename>name</filename></term><listitem><para>Used only

for alias handling. <filename>name</filename> should be the name of the application

whose options are being parsed, or should be NULL if no option aliasing is

desired.</para>

</listitem></varlistentry>

<varlistentry><term><filename>argc</filename>, <filename>argv</filename></term>

<listitem><para>Specifies the command-line arguments to parse. These arguments

are generally passed to <literal>poptGetContext()</literal> exactly as they

were passed to the application's <literal>main()</literal> function.</para>

</listitem></varlistentry>

<varlistentry><term><filename>options</filename></term><listitem><para>Points

to the table of command-line options. See the Option Tables section above.

</para>

</listitem></varlistentry>

<varlistentry><term><filename>flags</filename></term><listitem><para>Can take

one of the following values:</para>

<variablelist>

<varlistentry><term>POPT_CONTEXT_NO_EXEC</term><listitem><para>Ignore <literal>

exec</literal> expansions</para>

</listitem></varlistentry>

<varlistentry><term>POPT_CONTEXT_KEEP_FIRST</term><listitem><para>Do not ignore <literal>

argv[0]</literal></para>

</listitem></varlistentry>

<varlistentry><term>POPT_CONTEXT_POSIXMEHARDER</term><listitem><para>Options

cannot follow arguments</para>

</listitem></varlistentry>

</variablelist></listitem></varlistentry>

</variablelist><para>A <literal>poptContext</literal> keeps track of which

options have already been parsed and which remain to be parsed. If an application

wishes to restart processing the options of a set of arguments, the application

can reset the <literal>poptContext</literal> by passing the context as the

sole argument to <literal>poptResetContext()</literal>.</para>

<para>When argument processing is complete, the process should free the <literal>

poptContext</literal>, as it contains dynamically allocated components. The <literal>

poptFreeContext()</literal> function takes a <literal>poptContext</literal>

as its sole argument and frees the resources that the context is using.</para>

<para>Here are the prototypes of both <literal>poptResetContext()</literal>

and <literal>poptFreeContext()</literal>:</para>

<programlisting>#include &lt;popt.h>

void poptFreeContext(poptContext con);

void poptResetContext(poptContext con);</programlisting>

</refsect2>

<refsect2 id="libpopt-3-exde-cmdl">

<title>Parsing the Command Line</title>

<para>After an application has created a <literal>poptContext</literal>, the <literal>

poptContext</literal> may begin parsing arguments. <literal>poptGetNextOpt()

</literal> performs the actual argument parsing:</para>

<programlisting>#include &lt;popt.h>

int poptGetNextOpt(poptContext con);</programlisting>

<para>Taking the context as its sole argument, the <literal>poptGetNextOpt()

</literal> function parses the next command-line argument found. When <literal>

poptGetNextOpt()</literal> finds the next argument in the option table, the

function populates the object pointed to by the option table entry's <literal>

arg</literal> pointer, if the pointer is not NULL. If the <literal>val</literal>

entry for the option is not zero, the function returns that value. Otherwise, <literal>

poptGetNextOpt()</literal> continues to the next argument.</para>

<para><literal>poptGetNextOpt()</literal> returns &minus;1 when the final

argument has been parsed, and other negative values when errors occur. Therefore,

you should ensure that the <literal>val</literal> elements in the option table

are greater than 0.</para>

<para>If all of the command-line options are handled through <literal>arg

</literal> pointers, command-line parsing is reduced to the following line

of code:</para>

<programlisting>rc = poptGetNextOpt(poptcon);</programlisting>

<para>Many applications require more complex command-line parsing than this,

however, and use the following structure:</para>

<programlisting>while ((rc = poptGetNextOpt(poptcon)) > 0) {

switch (rc) {

/* specific arguments are handled here */

}

}</programlisting>

<para>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 these values:</para>

<itemizedlist>

<listitem><para>Ask <filename>popt</filename> to populate a variable with

the value of the option from the option table's <literal>arg</literal> elements.

</para></listitem>

<listitem><para>Use <literal>poptGetOptArg()</literal>:<programlisting>#include &lt;popt.h>

const char * poptGetOptArg(poptContext con);</programlisting></para></listitem>

</itemizedlist>

<para>The <literal>poptGetOptArg()</literal> function returns the argument

given for the final option returned by <literal>poptGetNextOpt()</literal>,

or returns NULL if no argument was specified.</para>

</refsect2>

<refsect2 id="libpopt-3-exde-larg">

<title>Leftover Arguments</title>

<para>Many applications take an arbitrary number of command-line arguments,

such as a list of file names. When <filename>popt</filename> encounters an

argument that does not begin with a hyphen, <filename>popt</filename> assumes

that this is such an argument, and adds the argument to a list of leftover

arguments. Three functions allow applications to access such arguments:</para>

<variablelist termlength="wholeline">

<varlistentry><term><literal>const char * poptGetArg(poptContext con);</literal></term>

<listitem><para>Returns the next leftover argument and marks the argument

as processed.</para>

</listitem></varlistentry>

<varlistentry><term><literal>const char * poptPeekArg(poptContext con);</literal></term>

<listitem><para>Returns the next leftover argument but does not mark the argument

as processed. This allows an application to look ahead into the argument list,

without modifying the list.</para>

</listitem></varlistentry>

<varlistentry><term><literal>const char ** poptGetArgs(poptContext con);</literal></term>

<listitem><para>Returns all of the leftover arguments in a manner identical

to <literal>argv</literal>. The final element in the returned array points

to NULL, indicating the end of the arguments.</para>

</listitem></varlistentry>

</variablelist></refsect2>

<refsect2 id="libpopt-3-exde-help">

<title>Automatic Help Messages</title>

<para>The popt library can automatically generate help messages that describe

the options that an application accepts. Two types of help messages can be

generated:</para>

<itemizedlist>

<listitem><para>Usage messages are short messages that list valid options,

but do not describe the options.</para></listitem>

<listitem><para>Help messages describe each option in one or more lines, resulting

in a longer but more useful message.</para></listitem>

</itemizedlist>

<para>Whenever automatic help messages are used, the <literal>descrip</literal>

and <literal>argDescrip</literal> members of the <literal>struct poptOption

</literal> structure should be populated for each option.</para>

<para>The POPT_AUTOHELP macro makes it easy to add usage and help messages

to your application, as described earlier in this man page. If you need more

control over your help messages, use the following functions:</para>

<programlisting>#include &lt;popt.h>

void poptPrintHelp(poptContext con, FILE * f, int flags);

void poptPrintUsage(poptContext con, FILE * f, int flags);</programlisting>

<para><literal>poptPrintHelp()</literal> displays the standard help message

to the <literal>stdio</literal> file descriptor <literal>f</literal>, while <literal>

poptPrintUsage()</literal> displays the shorter usage message. Both functions

currently ignore the <literal>flags</literal> argument, which is provided

for future functionality.</para>

</refsect2>

<refsect2 id="libpopt-3-exde-alia">

<title>Option Aliasing</title>

<para>One of the primary benefits of <filename>popt</filename> is the ability

to use option aliasing. Option aliasing allows the user to specify options

that <filename>popt</filename> expands into other options. For example. if

the standard <command>grep</command> command made use of <filename>popt</filename>,

users could add a <option>&minus;text</option> option that expanded to <literal>

-i -n -E -2</literal>, to allow users to more easily find information in text

files.</para>

<refsect3 id="libpopt-3-exde-alia-spec">

<title>Specifying Aliases</title>

<para>Aliases are normally specified in two places: <itemizedlist>

<listitem><para><filename>/etc/popt</filename></para></listitem>

<listitem><para><filename>$HOME/.popt</filename></para></listitem>

</itemizedlist></para>

<para>Both files have the same format, that is, an arbitrary number of lines

formatted as follows: <screen><replaceable>appname</replaceable> alias <replaceable>

newoption</replaceable> <replaceable>expansion</replaceable></screen></para>

<para>An alias specification is composed of the following elements:<variablelist>

<varlistentry><term><replaceable>appname</replaceable></term><listitem><para>

Specifies the name of the application, which must be the same as the <literal>

name</literal> parameter passed to <literal>poptGetContext()</literal>. This

allows each file to specify aliases for multiple programs.</para>

</listitem></varlistentry>

<varlistentry><term>alias</term><listitem><para>Specifies that an alias is

being defined. Currently, <literal>popt</literal> configuration files support

only aliases, but other abilities may be added in the future.</para>

</listitem></varlistentry>

<varlistentry><term><replaceable>newoption</replaceable></term><listitem>

<para>Specifies the option that should be aliased, either a short option or

a long option.</para>

</listitem></varlistentry>

<varlistentry><term><replaceable>expansion</replaceable></term><listitem>

<para>Specifies the expansion for the alias. The expansion is parsed in a

similar way to a shell command: backslashes are allowed, and single quotation

marks can 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 a shell command.</para>

</listitem></varlistentry>

</variablelist></para>

<para>For example, the following entry would add to the <command>grep</command>

command the <option>&minus;text</option> option described earlier:</para>

<para><computeroutput>grep alias --text -i -n -E -2</computeroutput></para>

</refsect3>

<refsect3 id="libpopt-3-exde-alia-enab">

<title>Enabling Aliases</title>

<para>An application must enable alias expansion for a <literal>poptContext

</literal>, before calling <literal>poptGetNextArg()</literal> for the first

time. Three functions define aliases for a context:</para>

<variablelist termlength="wholeline">

<varlistentry><term>int poptReadDefaultConfig(poptContext con, int flags);

</term><listitem><para>Reads aliases from <filename>/etc/popt</filename> and <filename>

$HOME/.popt</filename>. The <literal>flags</literal> argument should be NULL,

it is provided only for future expansion.</para>

</listitem></varlistentry>

<varlistentry><term>int poptReadConfigFile(poptContext con, char * fn);</term>

<listitem><para>Opens the file specified by <literal>fn</literal> and parses

the file as a <filename>popt</filename> configuration file. This allows applications

to use application-specific configuration files.</para>

</listitem></varlistentry>

<varlistentry><term>int poptAddAlias(poptContext con, struct poptAlias alias,

int flags);</term><listitem><para>Adds a new alias to a context. This function

is useful when processes want to specify aliases without having to read them

from a configuration file. The <literal>flags</literal> argument should be

0, it is provided only for future expansion. The new alias is specified as

a <literal>struct poptAlias</literal>, which is defined as follows:</para>

<programlisting>struct poptAlias {

const char * longName; /* may be NULL */

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

int argc;

const char ** argv; /* must be free()able */

};</programlisting>

<para><literal>longName</literal> and <literal>shortName</literal> specify

the option that is aliased. <literal>argc</literal> and <literal>argv</literal>

define the expansion to use when the aliases option is encountered.</para>

</listitem></varlistentry>

</variablelist></refsect3>

</refsect2>

<refsect2 id="libpopt-3-exde-pars">

<title>Parsing Argument Strings</title>

<para><filename>popt</filename> usually parses arguments that are already

divided into an <literal>argv</literal>-style array. However, some applications

need to parse strings that are formatted identically to command lines. To

facilitate this, <literal>popt</literal> provides a function that parses a

string into an array of strings, using rules similar to those of normal shell

parsing:</para>

<programlisting>#include &lt;popt.h>

int poptParseArgvString(char * s, int * argcPtr,

char *** argvPtr);

int poptDupArgv(int argc, const char ** argv, int * argcPtr,

const char *** argvPtr);</programlisting>

<para>The string <literal>s</literal> is parsed into an <literal>argv</literal>-style

array. The integer pointed to by the <literal>argcPtr</literal> parameter

contains the number of elements parsed, and the final <literal>argvPtr</literal>

parameter contains the address of the newly created array. The routine <literal>

poptDupArgv()</literal> can be used to make a copy of an existing argument

array.</para>

<para>The <literal>argvPtr</literal> created by <literal>poptParseArgvString()

</literal> or <literal>poptDupArgv()</literal> can be passed directly to <literal>

poptGetContext()</literal>. Both routines return a single dynamically allocated

contiguous block of storage and should be freed using <literal>free()</literal>

when the application is finished with the storage.</para>

</refsect2>

<refsect2 id="libpopt-3-exde-earg">

<title>Handling Extra Arguments</title>

<para>Some applications implement the equivalent of option aliasing but do

so using special logic. The <literal>poptStuffArgs()</literal> function allows

an application to insert new arguments into the current <literal>poptContext

</literal>:</para>

<programlisting>#include &lt;popt.h>

int poptStuffArgs(poptContext con, const char ** argv);</programlisting>

<para>The passed <literal>argv</literal> must have a NULL pointer as its final

element. When <literal>poptGetNextOpt()</literal> is next called, the "stuffed"

arguments are the first to be parsed. <filename>popt</filename> returns to

the normal arguments when all of the stuffed arguments have been exhausted.

</para>

</refsect2>

</refsect1>

<refsect1 id="libpopt-3-erro"><title>&erro-tt;</title>

<para>All of the <filename>popt</filename> functions that can return errors

return integers. When an error occurs, a negative error code is returned.

The following error codes can occur:</para>

<variablelist>

<varlistentry><term>POPT_ERROR_BADNUMBER</term><listitem><para>A string-to-number

conversion failed because the string contains nonnumeric characters. This

occurs when <literal>poptGetNextOpt()</literal> is processing an argument

of type POPT_ARG_INT, POPT_ARG_LONG, POPT_ARG_FLOAT, or POPT_ARG_DOUBLE.</para>

</listitem></varlistentry>

<varlistentry><term>POPT_ERROR_BADOPT</term><listitem><para>An option was

specified in <literal>argv</literal> but is not in the option table. This

error can be returned only from <literal>poptGetNextOpt()</literal>.</para>

</listitem></varlistentry>

<varlistentry><term>POPT_ERROR_BADQUOTE</term><listitem><para>A parsed string

has a quotation mismatch, for example, a single quotation mark. <literal>

poptParseArgvString()</literal>, <literal>poptReadConfigFile()</literal>,

or <literal>poptReadDefaultConfig()</literal> can return this error.</para>

</listitem></varlistentry>

<varlistentry><term>POPT_ERROR_ERRNO</term><listitem><para>A system call returned

with an error, and <literal>errno</literal> still contains the error from

the system call. Both <literal>poptReadConfigFile()</literal> and <literal>

poptReadDefaultConfig()</literal> can return this error.</para>

</listitem></varlistentry>

<varlistentry><term>POPT_ERROR_NOARG</term><listitem><para>An option that

requires an argument was specified on the command line, but no argument was

given. This error can be returned only by <literal>poptGetNextOpt()</literal>.

</para>

</listitem></varlistentry>

<varlistentry><term>POPT_ERROR_OPTSTOODEEP</term><listitem><para>A set of

option aliases is nested too deeply. Currently, <filename>popt</filename>

follows options to only 10 levels, to prevent infinite recursion. Only <literal>

poptGetNextOpt()</literal> can return this error.</para>

</listitem></varlistentry>

<varlistentry><term>POPT_ERROR_OVERFLOW</term><listitem><para>A string-to-number

conversion failed because the number is too large or too small. This error

can occur only when <literal>poptGetNextOpt()</literal> is processing an

argument of type POPT_ARG_INT, POPT_ARG_LONG, POPT_ARG_FLOAT, or POPT_ARG_DOUBLE.

</para>

</listitem></varlistentry>

</variablelist><para>Two functions allow applications to provide good error

messages:</para>

<variablelist termlength="wholeline">

<varlistentry><term>const char *const poptStrerror(const int error);</term>

<listitem><para>Takes a <literal>popt</literal> error code and returns a string

describing the error, just as with the standard <literal>strerror()</literal>

function.</para>

</listitem></varlistentry>

<varlistentry><term>const char * poptBadOption(poptContext con, int flags);

</term><listitem><para>Returns the option that caused the error, if an error

occurred during <literal>poptGetNextOpt()</literal>. If the <literal>flags

</literal> argument is set to POPT_BADOPTION_NOALIAS, the outermost option

is returned. Otherwise, <literal>flags</literal> should be 0, and the option

that is returned may have been specified through an alias.</para>

</listitem></varlistentry>

</variablelist><para>These two functions ensure that <literal>popt</literal>

error handling is 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 <literal>poptStrerror()</literal>. When an error occurs during

argument parsing, code similar to the following displays a useful error message:

</para>

<programlisting>fprintf(stderr, "%s: %s\n",

poptBadOption(optCon, POPT_BADOPTION_NOALIAS),

poptStrerror(rc));</programlisting>

</refsect1>

<refsect1 id="libpopt-3-exam"><title>&exam-tt;</title>

<example role="example">

<title>Parse Program Created From robin Program</title>

<para>The following example is a simplified version of the <literal>robin

</literal> program that appears in Chapter 15 of &ldquo;Linux Application

Development&rdquo; by Michael K. Johnson and Erik W. Troan (copyright 1998

by Addison Wesley Longman, Inc.). The <literal>robin</literal> program has

been stripped of everything but its argument-parsing logic, slightly reworked,

and renamed <literal>parse</literal>. This program illustrates some of the

features of the extremely rich <filename>popt</filename> library.</para>

<programlisting>#include &lt;popt.h>

#include &lt;stdio.h>

void usage(poptContext optCon, int exitcode, char *error, char *addl) {

poptPrintUsage(optCon, stderr, 0);

if (error) fprintf(stderr, "%s: %s0, error, addl);

exit(exitcode);

}

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[] = {

{ "bps", 'b', POPT_ARG_INT, &amp;speed, 0,

"signaling rate in bits-per-second", "BPS" },

{ "crnl", 'c', 0, 0, 'c',

"expand cr characters to cr/lf sequences" },

{ "hwflow", 'h', 0, 0, 'h',

"use hardware (RTS/CTS) flow control" },

{ "noflow", 'n', 0, 0, 'n',

"use no flow control" },

{ "raw", 'r', 0, &amp;raw, 0,

"don't perform any character conversions" },

{ "swflow", 's', 0, 0, 's',

"use software (XON/XOF) flow control" } ,

POPT_AUTOHELP

{ NULL, 0, 0, NULL, 0 }

};

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

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

if (argc &lt; 2) {

poptPrintUsage(optCon, stderr, 0);

exit(1);

}

/* Now do options processing, get portname */

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

switch (c) {

case 'c':

buf[i++] = 'c';

break;

case 'h':

buf[i++] = 'h';

break;

case 's':

buf[i++] = 's';

break;

case 'n':

buf[i++] = 'n';

break;

}

}

portname = poptGetArg(optCon);

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

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

if (c &lt; -1) {

/* an error occurred during option processing */

fprintf(stderr, "%s: %s\n",

poptBadOption(optCon, POPT_BADOPTION_NOALIAS),

poptStrerror(c));

return 1;

}

/* Print out options, portname chosen */

printf("Options chosen: ");

for(j = 0; j &lt; i ; j++)

printf("-%c ", buf[j]);

if(raw) printf("-r ");

if(speed) printf("-b %d ", speed);

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

poptFreeContext(optCon);

exit(0);

}

</programlisting>

<para>RPM, a popular Linux package management application, uses several <filename>

popt</filename> features. Many RPM command-line arguments are implemented

using <filename>popt</filename> aliases, which makes RPM an excellent example

of how to take advantage of the <filename>popt</filename> library. For more

information about RPM, see <literal>http://www.rpm.org</literal>. The <filename>

popt</filename> source code distribution includes test programs that use all

of the features of the <filename>popt</filename> libraries in various ways.

If a <filename>popt</filename> feature does not work for you, check the <filename>

popt</filename> test code.</para>

</example>

</refsect1>

<refsect1 id="libpopt-3-file"><title>&file-tt;</title>

<para>The following files are used by this library:</para>

<variablelist termlength="medium">

<varlistentry><term><filename>/usr/lib/&cmd;.so</filename> </term><listitem>

<para>Command Line Parser API shared library</para>

</listitem></varlistentry>

</variablelist></refsect1>

<refsect1 id="libpopt-3-attr"><title>&attr-tt;</title>

<para>See <olink targetdocent="REFMAN5" localinfo="attributes-5"><citerefentry>

<refentrytitle>attributes</refentrytitle><manvolnum>5</manvolnum></citerefentry></olink>

for descriptions of the following attributes:</para>

<informaltable frame="all">

<tgroup cols="2" colsep="1" rowsep="1"><colspec colname="COLSPEC0" colwidth="1*">

<colspec colname="COLSPEC1" colwidth="1*">

<thead>

<row><entry align="center" valign="middle">ATTRIBUTE TYPE</entry><entry align="center"

valign="middle">ATTRIBUTE VALUE</entry></row>

</thead>

<tbody>

<row><entry><para>Availability</para></entry><entry><para>library/popt</para></entry>

</row>

<row><entry colname="COLSPEC0"><para>Interface stability</para></entry><entry

colname="COLSPEC1"><para>Volatile</para></entry></row>

</tbody>

</tgroup>

</informaltable>

</refsect1>

<refsect1 id="libpopt-3-also"><title>&also-tt;</title>

<para>

<citerefentry><refentrytitle>getopt</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>attributes</refentrytitle><manvolnum>5</manvolnum></citerefentry>

</para>

</refsect1>

<refsect1 id="libpopt-3-note"><title>&note-tt;</title>

<para>Updated by Erwann Chenede, Sun Microsystems Inc., 2003. Written by Erik

W. Troan (ewt@redhat.com), Michael K. Johnson, and Robert Lynch.</para>

</refsect1>

</refentry>