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GETCAP(3)              FreeBSD Library Functions Manual              GETCAP(3)

NAME
     cgetent, cgetset, cgetmatch, cgetcap, cgetnum, cgetstr, cgetustr,
     cgetfirst, cgetnext, cgetclose - capability database access routines

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <stdlib.h>

     int
     cgetent(char **buf, char **db_array, const char *name);

     int
     cgetset(const char *ent);

     int
     cgetmatch(const char *buf, const char *name);

     char *
     cgetcap(char *buf, const char *cap, int type);

     int
     cgetnum(char *buf, const char *cap, long *num);

     int
     cgetstr(char *buf, const char *cap, char **str);

     int
     cgetustr(char *buf, const char *cap, char **str);

     int
     cgetfirst(char **buf, char **db_array);

     int
     cgetnext(char **buf, char **db_array);

     int
     cgetclose(void);

DESCRIPTION
     The cgetent() function extracts the capability name from the database
     specified by the NULL terminated file array db_array and returns a
     pointer to a malloc(3)'d copy of it in buf.  The cgetent() function will
     first look for files ending in .db (see cap_mkdb(1)) before accessing the
     ASCII file.  The buf argument must be retained through all subsequent
     calls to cgetmatch(), cgetcap(), cgetnum(), cgetstr(), and cgetustr(),
     but may then be free(3)'d.  On success 0 is returned, 1 if the returned
     record contains an unresolved tc expansion, -1 if the requested record
     could not be found, -2 if a system error was encountered (could not
     open/read a file, etc.) also setting errno, and -3 if a potential
     reference loop is detected (see tc= comments below).

     The cgetset() function enables the addition of a character buffer
     containing a single capability record entry to the capability database.
     Conceptually, the entry is added as the first ``file'' in the database,
     and is therefore searched first on the call to cgetent().  The entry is
     passed in ent.  If ent is NULL, the current entry is removed from the
     database.  A call to cgetset() must precede the database traversal.  It
     must be called before the cgetent() call.  If a sequential access is
     being performed (see below), it must be called before the first
     sequential access call (cgetfirst or cgetnext()), or be directly preceded
     by a cgetclose() call.  On success 0 is returned and -1 on failure.

     The cgetmatch() function will return 0 if name is one of the names of the
     capability record buf, -1 if not.

     The cgetcap() function searches the capability record buf for the
     capability cap with type type.  A type is specified using any single
     character.  If a colon (`:') is used, an untyped capability will be
     searched for (see below for explanation of types).  A pointer to the
     value of cap in buf is returned on success, NULL if the requested
     capability could not be found.  The end of the capability value is
     signaled by a `:' or ASCII NUL (see below for capability database
     syntax).

     The cgetnum() function retrieves the value of the numeric capability cap
     from the capability record pointed to by buf.  The numeric value is
     returned in the long pointed to by num.  0 is returned on success, -1 if
     the requested numeric capability could not be found.

     The cgetstr() function retrieves the value of the string capability cap
     from the capability record pointed to by buf.  A pointer to a decoded,
     NUL terminated, malloc(3)'d copy of the string is returned in the char *
     pointed to by str.  The number of characters in the decoded string not
     including the trailing NUL is returned on success, -1 if the requested
     string capability could not be found, -2 if a system error was
     encountered (storage allocation failure).

     The cgetustr() function is identical to cgetstr() except that it does not
     expand special characters, but rather returns each character of the
     capability string literally.

     The cgetfirst() and cgetnext() functions comprise a function group that
     provides for sequential access of the NULL pointer terminated array of
     file names, db_array.  The cgetfirst() function returns the first record
     in the database and resets the access to the first record.  The
     cgetnext() function returns the next record in the database with respect
     to the record returned by the previous cgetfirst() or cgetnext() call.
     If there is no such previous call, the first record in the database is
     returned.  Each record is returned in a malloc(3)'d copy pointed to by
     buf.  Tc expansion is done (see tc= comments below).  Upon completion of
     the database 0 is returned, 1 is returned upon successful return of
     record with possibly more remaining (we have not reached the end of the
     database yet), 2 is returned if the record contains an unresolved tc
     expansion, -1 is returned if a system error occurred, and -2 is returned
     if a potential reference loop is detected (see tc= comments below).  Upon
     completion of database (0 return) the database is closed.

     The cgetclose() function closes the sequential access and frees any
     memory and file descriptors being used.  Note that it does not erase the
     buffer pushed by a call to cgetset().

CAPABILITY DATABASE SYNTAX
     Capability databases are normally ASCII and may be edited with standard
     text editors.  Blank lines and lines beginning with a `#' are comments
     and are ignored.  Lines ending with a `\' indicate that the next line is
     a continuation of the current line; the `\' and following newline are
     ignored.  Long lines are usually continued onto several physical lines by
     ending each line except the last with a `\'.

     Capability databases consist of a series of records, one per logical
     line.  Each record contains a variable number of `:'-separated fields
     (capabilities).  Empty fields consisting entirely of white space
     characters (spaces and tabs) are ignored.

     The first capability of each record specifies its names, separated by `|'
     characters.  These names are used to reference records in the database.
     By convention, the last name is usually a comment and is not intended as
     a lookup tag.  For example, the vt100 record from the termcap(5) database
     begins:

           d0|vt100|vt100-am|vt100am|dec vt100:

     giving four names that can be used to access the record.

     The remaining non-empty capabilities describe a set of (name, value)
     bindings, consisting of a names optionally followed by a typed value:

     name        typeless [boolean] capability name is present [true]
     nameTvalue  capability (name, T) has value value
     name@       no capability name exists
     nameT@      capability (name, T) does not exist

     Names consist of one or more characters.  Names may contain any character
     except `:', but it is usually best to restrict them to the printable
     characters and avoid use of graphics like `#', `=', `%', `@', etc.  Types
     are single characters used to separate capability names from their
     associated typed values.  Types may be any character except a `:'.
     Typically, graphics like `#', `=', `%', etc. are used.  Values may be any
     number of characters and may contain any character except `:'.

CAPABILITY DATABASE SEMANTICS
     Capability records describe a set of (name, value) bindings.  Names may
     have multiple values bound to them.  Different values for a name are
     distinguished by their types.  The cgetcap() function will return a
     pointer to a value of a name given the capability name and the type of
     the value.

     The types `#' and `=' are conventionally used to denote numeric and
     string typed values, but no restriction on those types is enforced.  The
     functions cgetnum() and cgetstr() can be used to implement the
     traditional syntax and semantics of `#' and `='.  Typeless capabilities
     are typically used to denote boolean objects with presence or absence
     indicating truth and false values respectively.  This interpretation is
     conveniently represented by:

           (getcap(buf, name, ':') != NULL)

     A special capability, tc= name, is used to indicate that the record
     specified by name should be substituted for the tc capability.  Tc
     capabilities may interpolate records which also contain tc capabilities
     and more than one tc capability may be used in a record.  A tc expansion
     scope (i.e., where the argument is searched for) contains the file in
     which the tc is declared and all subsequent files in the file array.

     When a database is searched for a capability record, the first matching
     record in the search is returned.  When a record is scanned for a
     capability, the first matching capability is returned; the capability
     :nameT@: will hide any following definition of a value of type T for
     name; and the capability :name@: will prevent any following values of
     name from being seen.

     These features combined with tc capabilities can be used to generate
     variations of other databases and records by either adding new
     capabilities, overriding definitions with new definitions, or hiding
     following definitions via `@' capabilities.

EXAMPLES
           example|an example of binding multiple values to names:\
                :foo%bar:foo^blah:foo@:\
                :abc%xyz:abc^frap:abc$@:\
                :tc=more:

     The capability foo has two values bound to it (bar of type `%' and blah
     of type `^') and any other value bindings are hidden.  The capability abc
     also has two values bound but only a value of type `$' is prevented from
     being defined in the capability record more.

           file1:
                new|new_record|a modification of "old":\
                     :fript=bar:who-cares@:tc=old:blah:tc=extensions:
           file2:
                old|old_record|an old database record:\
                     :fript=foo:who-cares:glork#200:

     The records are extracted by calling cgetent() with file1 preceding
     file2.  In the capability record new in file1, fript=bar overrides the
     definition of fript=foo interpolated from the capability record old in
     file2, who-cares@ prevents the definition of any who-cares definitions in
     old from being seen, glork#200 is inherited from old, and blah and
     anything defined by the record extensions is added to those definitions
     in old.  Note that the position of the fript=bar and who-cares@
     definitions before tc=old is important here.  If they were after, the
     definitions in old would take precedence.

CGETNUM AND CGETSTR SYNTAX AND SEMANTICS
     Two types are predefined by cgetnum() and cgetstr():

     name#number  numeric capability name has value number
     name=string  string capability name has value string
     name#@       the numeric capability name does not exist
     name=@       the string capability name does not exist

     Numeric capability values may be given in one of three numeric bases.  If
     the number starts with either `0x' or `0X' it is interpreted as a
     hexadecimal number (both upper and lower case a-f may be used to denote
     the extended hexadecimal digits).  Otherwise, if the number starts with a
     `0' it is interpreted as an octal number.  Otherwise the number is
     interpreted as a decimal number.

     String capability values may contain any character.  Non-printable ASCII
     codes, new lines, and colons may be conveniently represented by the use
     of escape sequences:

     ^X        ('X' & 037)          control-X
     \b, \B    (ASCII 010)          backspace
     \t, \T    (ASCII 011)          tab
     \n, \N    (ASCII 012)          line feed (newline)
     \f, \F    (ASCII 014)          form feed
     \r, \R    (ASCII 015)          carriage return
     \e, \E    (ASCII 027)          escape
     \c, \C    (:)                  colon
     \\        (\)                  back slash
     \^        (^)                  caret
     \nnn      (ASCII octal nnn)

     A `\' may be followed by up to three octal digits directly specifies the
     numeric code for a character.  The use of ASCII NULs, while easily
     encoded, causes all sorts of problems and must be used with care since
     NULs are typically used to denote the end of strings; many applications
     use `\200' to represent a NUL.

DIAGNOSTICS
     The cgetent(), cgetset(), cgetmatch(), cgetnum(), cgetstr(), cgetustr(),
     cgetfirst(), and cgetnext() functions return a value greater than or
     equal to 0 on success and a value less than 0 on failure.  The cgetcap()
     function returns a character pointer on success and a NULL on failure.

     The cgetent(), and cgetset() functions may fail and set errno for any of
     the errors specified for the library functions: fopen(3), fclose(3),
     open(2), and close(2).

     The cgetent(), cgetset(), cgetstr(), and cgetustr() functions may fail
     and set errno as follows:

     [ENOMEM]           No memory to allocate.

SEE ALSO
     cap_mkdb(1), malloc(3)

BUGS
     Colons (`:') cannot be used in names, types, or values.

     There are no checks for tc=name loops in cgetent().

     The buffer added to the database by a call to cgetset() is not unique to
     the database but is rather prepended to any database used.

FreeBSD 11.0-PRERELEASE         March 22, 2002         FreeBSD 11.0-PRERELEASE

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | CAPABILITY DATABASE SYNTAX | CAPABILITY DATABASE SEMANTICS | EXAMPLES | CGETNUM AND CGETSTR SYNTAX AND SEMANTICS | DIAGNOSTICS | SEE ALSO | BUGS

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