GETCAP(3) BSD Library Functions Manual GETCAP(3)NAME
cgetent, cgetset, cgetmatch, cgetcap, cgetnum, cgetstr, cgetustr,
cgetfirst, cgetnext, cgetclose — capability database access routines
cgetent(char **buf, char **db_array, char *name);
cgetmatch(char *buf, char *name);
cgetcap(char *buf, char *cap, char type);
cgetnum(char *buf, char *cap, long *num);
cgetstr(char *buf, char *cap, char **str);
cgetustr(char *buf, char *cap, char **str);
cgetfirst(char **buf, char **db_array);
cgetnext(char **buf, char **db_array);
DESCRIPTIONCgetent() 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
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 was
encountered (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
numeric 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‐
Cgetustr is identical to cgetstr except that it does not expand special
characters, but rather returns each character of the capability string
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 data‐
base 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 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 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 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
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‐
(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.
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 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 numericcapability namehas value number
name=string string capabilitynamehas value string
name#@ the numeric capabilitynamedoes not exist
name=@ the string capabilitynamedoes 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 hexadeci‐
mal 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 inter‐
preted as a decimal number.
String capability values may contain any character. Non-printable
ASCIIcodes, 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 ASCIINULs,while easily encoded,
causes all sorts of problems and must be used with care since NULsare
typically used to denote the end of strings; many applications use `\200'
to represent a NUL.
cgetnextreturn a value greater than or equal to 0 on success and a value
less than 0 on failure. Cgetcapreturns a character pointer on success
and a NULLon failure.
Cgetent,and cgetseqmay fail and set errnofor any of the errors specified
for the library functions: fopen(2),fclose(2),open(2),and close(2).
Cgetent,cgetset,cgetstr,and cgetustrmay fail and set errnoas follows:
[ENOMEM] No memory to allocate.
Colons (`:') can't be used in names, types, or values.
There are no checks for tc=nameloops in cgetent.
The buffer added to the database by a call to cgetsetis not unique to the
database but is rather prepended to any database used.
BSD February 17, 2019 BSD