getcap(3) BSD Library Functions Manual getcap(3)
NAME
cgetent, cgetset, cgetmatch, cgetcap, cgetnum, cgetstr, cgetustr,
cgetfirst, cgetnext, cgetclose -- capability database access routines
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdlib.h>
int
cgetent(char **buf, char **db_array, const char *name);
int
cgetset(const char *ent);
int
cgetmatch(const char *buf, const char *name);
char *
cgetcap(char *buf, const char *cap, int type);
int
cgetnum(char *buf, const char *cap, long *num);
int
cgetstr(char *buf, const char *cap, char **str);
int
cgetustr(char *buf, const char *cap, char **str);
int
cgetfirst(char **buf, char **db_array);
int
cgetnext(char **buf, char **db_array);
int
cgetclose(void);
DESCRIPTION
The cgetent() function extracts the capability name from the database
specified by the NULL terminated file array db_array and returns a
pointer to a malloc(3)'d copy of it in buf. The cgetent() function will
first look for files ending in .db (see cap_mkdb(1)) before accessing the
ASCII file. The buf argument must be retained through all subsequent
calls to cgetmatch(), cgetcap(), cgetnum(), cgetstr(), and cgetustr(),
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
could not be found, -2 if a system error was encountered (could not
open/read a file, etc.) also setting errno, and -3 if a potential refer-
ence loop is detected (see tc= comments below).
The cgetset() function enables the addition of a character buffer con-
taining 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. A call to 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 sequen-
tial access call (cgetfirst() or cgetnext()), or be directly preceded by
a cgetclose() call. On success 0 is returned and -1 on failure.
The cgetmatch() function will return 0 if name is one of the names of the
capability record buf, -1 if not.
The cgetcap() function searches the capability record buf for the capa-
bility cap with type type. A type is specified using any single charac-
ter. 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 could not
be found. The end of the capability value is signaled by a `:' or ASCII
NUL (see below for capability database syntax).
The cgetnum() function 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. 0 is returned on success, -1 if
the requested numeric capability could not be found.
The cgetstr() function 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 could not be found, -2 if a system error was encoun-
tered (storage allocation failure).
The cgetustr() function is identical to cgetstr() except that it does not
expand special characters, but rather returns each character of the capa-
bility string literally.
The cgetfirst() and cgetnext() functions comprise a function group that
provides for sequential access of the NULL pointer terminated array of
file names, db_array. The cgetfirst() function returns the first record
in the database and resets the access to the first record. The
cgetnext() function 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(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
record with possibly more remaining (we have not reached the end of the
database 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.
The cgetclose() function closes the sequential access and frees any mem-
ory 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(5) 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 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 is 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 asso-
ciated typed values. Types may be any character except a `:'. Typi-
cally, 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. The cgetcap() function 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 tradi-
tional syntax and semantics of `#' and `='. Typeless capabilities are
typically used to denote boolean objects with presence or absence indi-
cating truth and false values respectively. This interpretation is con-
veniently represented 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 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.
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 hexa-
decimal 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 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
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.
DIAGNOSTICS
The cgetent(), cgetset(), cgetmatch(), cgetnum(), cgetstr(), cgetustr(),
cgetfirst(), and cgetnext() functions return a value greater than or
equal to 0 on success and a value less than 0 on failure. The cgetcap()
function returns a character pointer on success and a NULL on failure.
The cgetent(), and cgetset() functions may fail and set errno for any of
the errors specified for the library functions: fopen(3), fclose(3),
open(2), and close(2).
The cgetent(), cgetset(), cgetstr(), and cgetustr() functions may fail
and set errno as follows:
[ENOMEM] No memory to allocate.
SEE ALSO
cap_mkdb(1), malloc(3)
BUGS
Colons (`:') 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.
BSD March 22, 2002 BSD
Mac OS X 10.8 - Generated Mon Aug 27 18:44:11 CDT 2012