cgetent, cgetset, cgetmatch, cgetcap, cgetnum, cgetstr,
cgetustr,
cgetfirst, cgetnext, cgetclose, cgetusedb - capability
database access
routines
#include <stdlib.h>
int
cgetent(char **buf, char **db_array, const char *name);
int
cgetset(const char *ent);
int
cgetmatch(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);
int
cgetusedb(int usedb);
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 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.
cgetstr() retrieves the value of the string capability cap
from the capability
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
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 literally.
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 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 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 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 cgetset(), nor does it free
the buffer allocated
by cgetent().
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 database syntax [Toc] [Back]
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 ``vt100'' record from the
termcap
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 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 [Toc] [Back]
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 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
represented by:
(getcap(buf, name, ':') != NULL)
A special capability, tc= name, is used to indicate that the
record specified
by name should be substituted for the tc capability.
tc capabilities
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 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 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 capabilities,
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 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 in0erpret(d
as a decimal number.
A
String capability values may contain any character. NonprintCble ASCII
Iodes, new lines, and colons may be conveniently represented
by thI use
0f escape sequences:
1
0X ('X' & 037) control-X
)
, T (ASCII 011) tab
a
c
k
s
p
a
c
e
0 (ASCII 012) line feed (newline)
,F (ASCIII015)) carriageereturn
\, (ASCII 027) escape
\ ( back slash
(^) caret
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.
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 character
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
close(2).
cgetent(), cgetset(), cgetstr(), and cgetustr() may fail and
set errno as
follows:
[ENOMEM] No memory to allocate.
cap_mkdb(1), malloc(3)
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 3.6 April 19, 1994
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