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GETCAP(3)                   BSD Programmer's Manual                  GETCAP(3)

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

SYNOPSIS
     #include <&lt;stdlib.h>&gt;

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

     int
     cgetset(char *ent);

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

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

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

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

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

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

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

     int
     cgetclose(void);

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

     Cgetset 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.  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.

     Cgetmatch will return 0 if name is one of the names of the capability
     record buf, -1 if not.


     Cgetcap 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 couldn't be found.  The end
     of the capability value is signaled by a `:' or ASCII NUL (see below for
     capability database syntax).

     Cgetnum retrieves the value of the numeric capability cap from the capa-
     bility 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 nu-
     meric capability couldn't be found.

     Cgetstr retrieves the value of the string capability cap from the capa-
     bility record pointed to by buf. A pointer to a decoded, NUL terminated,
     malloc'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
     couldn't be found, -2 if a system error was encountered (storage alloca-
     tion failure).

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

     Cgetfirst, cgetnext, comprise a function group that provides for sequen-
     tial access of the NULL pointer terminated array of file names, db_array.
     Cgetfirst returns the first record in the database and resets the access
     to the first record.  Cgetnext 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'd  copy point-
     ed to by buf. Tc expansion is done (see tc= comments below).  Upon com-
     pletion of the database 0 is returned,  1 is returned upon successful re-
     turn of record with possibly more remaining (we haven't reached the end
     of the database yet), 2 is returned if the record contains an unresolved
     tc expansion, -1 is returned if an system error occurred, and -2 is re-
     turned if a potential reference loop is detected (see tc= comments be-
     low).  Upon completion of database (0 return) the database is closed.

     Cgetclose closes the sequential access and frees any memory and file de-
     scriptors 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 ig-
     nored.  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 charac-
     ters (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 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 values:

     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's usually best to restrict them to the printable char-
     acters 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 dis-
     tinguished by their types. Cgetcap 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 rep-
     resented by:

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

     A special capability, tc= name, is used to indicate that the record spec-
     ified by name should be substituted for the tc capability.  Tc capabili-
     ties 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 capa-
     bility, 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 capabili-
     ties, 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 de-
     fined 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 hex-
     adecimal 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 interpret-
     ed 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 encod-
     ed, 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
     Cgetent, cgetset, cgetmatch, cgetnum, cgetstr, cgetustr, cgetfirst, and
     cgetnext return a value greater than or equal to 0 on success and a value
     less than 0 on failure.  Cgetcap returns a character pointer on success
     and a NULL on failure.

     Cgetent, and cgetseq may fail and set errno for any of the errors speci-
     fied for the library functions: fopen(2),  fclose(2),  open(2),  and
     close(2).

     Cgetent, cgetset, cgetstr, and cgetustr may fail and set errno as fol-

     lows:

     [ENOMEM]      No memory to allocate.

SEE ALSO
     cap_mkdb(1),  malloc(3)

BUGS
     Colons (`:') can't 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.

4.4BSD                           May 13, 1994                                5