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+
+=pod
+
+=head1 NAME
+
+config - OpenSSL CONF library configuration files
+
+=head1 DESCRIPTION
+
+The OpenSSL CONF library can be used to read configuration files.
+It is used for the OpenSSL master configuration file B<openssl.cnf>
+and in a few other places like B<SPKAC> files and certificate extension
+files for the B<x509> utility.
+
+A configuration file is divided into a number of sections. Each section
+starts with a line B<[ section_name ]> and ends when a new section is
+started or end of file is reached. A section name can consist of
+alphanumeric characters and underscores.
+
+The first section of a configuration file is special and is referred
+to as the B<default> section this is usually unnamed and is from the
+start of file until the first named section. When a name is being looked up
+it is first looked up in a named section (if any) and then the
+default section.
+
+The environment is mapped onto a section called B<ENV>.
+
+Comments can be included by preceding them with the B<#> character
+
+Each section in a configuration file consists of a number of name and
+value pairs of the form B<name=value>
+
+The B<name> string can contain any alphanumeric characters as well as
+a few punctuation symbols such as B<.> B<,> B<;> and B<_>.
+
+The B<value> string consists of the string following the B<=> character
+until end of line with any leading and trailing white space removed.
+
+The value string undergoes variable expansion. This can be done by
+including the form B<$var> or B<${var}>: this will substitute the value
+of the named variable in the current section. It is also possible to
+substitute a value from another section using the syntax B<$section::name>
+or B<${section::name}>. By using the form B<$ENV::name> environment
+variables can be substituted. It is also possible to assign values to
+environment variables by using the name B<ENV::name>, this will work
+if the program looks up environment variables using the B<CONF> library
+instead of calling B<getenv()> directly.
+
+It is possible to escape certain characters by using any kind of quote
+or the B<\> character. By making the last character of a line a B<\>
+a B<value> string can be spread across multiple lines. In addition
+the sequences B<\n>, B<\r>, B<\b> and B<\t> are recognised.
+
+=head1 NOTES
+
+If a configuration file attempts to expand a variable that doesn't exist
+then an error is flagged and the file will not load. This can happen
+if an attempt is made to expand an environment variable that doesn't
+exist. For example the default OpenSSL master configuration file used
+the value of B<HOME> which may not be defined on non Unix systems.
+
+This can be worked around by including a B<default> section to provide
+a default value: then if the environment lookup fails the default value
+will be used instead. For this to work properly the default value must
+be defined earlier in the configuration file than the expansion. See
+the B<EXAMPLES> section for an example of how to do this.
+
+If the same variable exists in the same section then all but the last
+value will be silently ignored. In certain circumstances such as with
+DNs the same field may occur multiple times. This is usually worked
+around by ignoring any characters before an initial B<.> e.g.
+
+ 1.OU="My first OU"
+ 2.OU="My Second OU"
+
+=head1 EXAMPLES
+
+Here is a sample configuration file using some of the features
+mentioned above.
+
+ # This is the default section.
+ 
+ HOME=/temp
+ RANDFILE= ${ENV::HOME}/.rnd
+ configdir=$ENV::HOME/config
+
+ [ section_one ]
+
+ # We are now in section one.
+
+ # Quotes permit leading and trailing whitespace
+ any = " any variable name "
+
+ other = A string that can \
+ cover several lines \
+ by including \\ characters
+
+ message = Hello World\n
+
+ [ section_two ]
+
+ greeting = $section_one::message
+
+This next example shows how to expand environment variables safely.
+
+Suppose you want a variable called B<tmpfile> to refer to a
+temporary filename. The directory it is placed in can determined by
+the the B<TEMP> or B<TMP> environment variables but they may not be
+set to any value at all. If you just include the environment variable
+names and the variable doesn't exist then this will cause an error when
+an attempt is made to load the configuration file. By making use of the
+default section both values can be looked up with B<TEMP> taking 
+priority and B</tmp> used if neither is defined:
+
+ TMP=/tmp
+ # The above value is used if TMP isn't in the environment
+ TEMP=$ENV::TMP
+ # The above value is used if TEMP isn't in the environment
+ tmpfile=${ENV::TEMP}/tmp.filename
+
+=head1 BUGS
+
+Currently there is no way to include characters using the octal B<\nnn>
+form. Strings are all null terminated so nulls cannot form part of
+the value.
+
+The escaping isn't quite right: if you want to use sequences like B<\n>
+you can't use any quote escaping on the same line.
+
+Files are loaded in a single pass. This means that an variable expansion
+will only work if the variables referenced are defined earlier in the
+file.
+
+=head1 SEE ALSO
+
+x509(1), req(1), ca(1)
+
+=cut