capability database access
**db_array, const char
*buf, const char
*buf, const char
*buf, const char
*buf, const char
*buf, const char
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
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
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 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).
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
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 (
cgetnext()), or be directly preceded by a
cgetclose() call. On success 0 is returned and -1 on
will return 0 if name is one of the names of the
capability record buf, -1 if not.
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
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).
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. On success 0 is returned, -1 if the requested
numeric capability couldn't be found.
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 couldn't be
found, or -2 if a system error was encountered (storage allocation
is identical to
cgetstr() except that it does not
expand special characters, but rather returns each character of the
capability string literally.
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 access to the first record.
cgetnext() returns the next record in the database
with respect to the record returned by the previous
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 a record with
possibly more remaining (the end of the database has not been reached 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.
closes the file descriptor and resets state used for sequential access. If
cgetfirst() nor the
cgetnext() functions have been called,
cgetclose() has no effect. Note that it does not
erase the buffer pushed by a call to
does it free the buffer allocated by
allows the user to specify whether to use or ignore database files ending in
“.db”. If usedb is zero, files ending in
“.db” will be ignored. If usedb is
non-zero, files ending in “.db” will be used in preference to
the text version. The default is to process “.db” files.
cgetusedb() returns the previous setting.
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 colon-separated fields (capabilities). Empty fields consisting entirely of whitespace 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 “vt220” record
termcap database begins with
giving two names that can be used to access this record.
The remaining non-empty capabilities describe a set of (name, value) bindings, consisting of a name 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's 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.
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
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:
(cgetcap(buf, name, ':') != NULL)
A special capability,
tc= name, is used to
indicate that the record specified by name should be
substituted for the
tc capabilities may interpolate records which also
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
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
:name@: will prevent any following values
of name from being seen.
These features combined with
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 ‘@’
cgetnum() and cgetstr() syntax and semantics
Two types are predefined by
|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’, 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|
|\nnn||(ASCII octal nnn)|
A ‘\’ 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.
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.
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
NULL on failure.
cgetset() may fail and set
errno for any of the errors specified for the library
functions fopen(3), fclose(3), open(2), and close(2).
cgetustr() may fail and set
errno as follows:
- No memory to allocate.
Colon (‘:’) characters or vertical bar (‘|’) characters cannot be used in names.
There are no checks for
tc= name loops in
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.