|CGETENT(3)||Library Functions Manual||CGETENT(3)|
cgetusedb — capability
database access routines
**db_array, const char
*buf, const char
*buf, const char
*buf, const char
*buf, const char
*buf, const char
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
cgetustr(), but may then be
free(3)'d. On success 0 is returned, 1 if
the returned record contains an unresolved
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
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
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
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 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
cgetstr() 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 failure).
cgetustr() is identical to
cgetstr() except that it does not expand special
characters, but rather returns each character of the capability string
cgetnext() comprise a function group that provides
for sequential access of the null-terminated array of file names,
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
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 an 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.
cgetclose() closes the file descriptor and
resets state used for sequential access. If neither the
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
cgetusedb() 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 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 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.
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
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
(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 ‘@’
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.
cgetustr() may fail and set
errno as follows:
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.
|September 2, 2019||OpenBSD-current|