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, char *name);
int
cgetset(char *ent);
int
cgetmatch(char *buf, char *name);
char *
cgetcap(char *buf, char *cap, int type);
int
cgetnum(char *buf, char *cap, long *num);
int
cgetstr(char *buf, char *cap, char **str);
int
cgetustr(char *buf, 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 re
turns 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 re
quested 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 po
tential reference loop is detected (see tc= comments below).
The cgetset() function 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. 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 sequential 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 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 capa
bility 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 ca
pability 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 encountered (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 capability string literally.
The cgetfirst() and cgetnext() functions comprise a function
group that provides for sequential access of the NULL pointer terminat
ed 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 unre
solved 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 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 `:'-sepa
rated fields (capabilities). Empty fields consisting entirely of white
space 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 term
cap(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 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. The cgetcap() function will re
turn 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 nu
meric 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 capa
bilities are typically used to denote boolean objects with presence or
absence indicating truth and false values respectively. This interpre
tation 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

ties may interpolate records which also contain tc capabili
ties and more than one tc capability may be used in a record. A tc expan
sion 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 capa
bility
: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.

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 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 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 nu
meric 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 in0er(reted as a decimal number. A String capability values may contain any character. Non
printCble 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 0 (ASCII 012) line feed (newline) ,F (ASCIII015)) carriageereturn k s (ASCII 027) escape p ( back slash a (^) caret 0n (ASCII octal nnn) e 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 cgetseq() 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() func
tions may fail and set errno as follows:
[ENOMEM] No memory to allocate.

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 May 13, 1994

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