GETCAP(3) OpenBSD Programmer's Manual GETCAP(3)
cgetent, cgetset, cgetmatch, cgetcap, cgetnum, cgetstr, cgetustr,
cgetfirst, cgetnext, cgetclose - capability database access routines
cgetent(char **buf, char **db_array, const char *name);
cgetset(const char *ent);
cgetmatch(char *buf, const char *name);
cgetcap(char *buf, const char *cap, int type);
cgetnum(char *buf, const char *cap, long *num);
cgetstr(char *buf, const char *cap, char **str);
cgetustr(char *buf, const char *cap, char **str);
cgetfirst(char **buf, char **db_array);
cgetnext(char **buf, char **db_array);
The cgetent() function extracts the capability record name from the
database specified by the null-terminated file array db_array and returns
a pointer to a copy of it in buf. cgetent() will first look for files
ending in ``.db'' (see cap_mkdb(1)) before accessing the ASCII version
of the capability database. 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 returned, 1 if the returned
record contains an unresolved tc expansion, -1 if the requested record
couldn't be found, -2 if a system error occurred (couldn't open or read a
file, for example) 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 cgetent().
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 or 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 ca-
pability record pointed to by buf. The numeric value is returned in the
long pointed to by num. On success 0 is returned, -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, null-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 trail-
ing NUL) is returned on success, -1 if the requested string capability
couldn't be found, or -2 if a system error was encountered (storage allo-
cgetustr() is identical to cgetstr() except that it does not expand spe-
cial characters, but rather returns each character of the capability
cgetfirst() and cgetnext() comprise a function group that provides for
sequential access of the null-terminated array of file names, db_array.
cgetfirst() returns the first record in the database and resets the ac-
cess 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
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 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
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 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 colon-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
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, graph-
ics like `#', `=', `%', etc. are used. Values may be any number of char-
acters 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 tradition-
al syntax and semantics of `#' and `='. Typeless capabilities are typi-
cally used to denote boolean objects with presence or absence indicating
truth and false values respectively. This interpretation is conveniently
(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.
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.
example|an example of binding multiple values to names:\
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.
new|new_record|a modification of "old":\
old|old_record|an old database record:\
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 any-
thing 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.
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 charac-
ter pointer on success and a NULL on failure.
cgetent() and cgetset() may fail and set errno for any of the errors
specified for the library functions fopen(3), fclose(3), open(2), and
cgetent(), cgetset(), cgetstr(), and cgetustr() may fail and set errno as
[ENOMEM] No memory to allocate.
Colon (`:') characters 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.
OpenBSD 2.6 April 19, 1994 5
Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.