SNOBOL4DBM(1)SNOBOL4DBM(1)NAMEsnobol4dbm - SNOBOL4 NDBM interface
SYNOPSIS-INCLUDE 'ndbm.sno'
dbhandle = DBM_OPEN(file,flags,mode)
DBM_CLOSE(dbhandle)
DBM_STORE(dbhandle,key,datum,flags)
datum = DBM_FETCH(dbhandle,key)
DBM_DELETE(dbhandle,key)
key = DBM_FIRSTKEY(dbhandle)
key = DBM_NEXTKEY(dbhandle)DBM_ERROR(dbhandle)DBM_CLEARERR(dbhandle)DESCRIPTION
"NDBM" (for New Data Base Managemnt) is an industry standard fast
hashed storage API first created in 4.3BSD, and included in the Unix 98
(SUSv2) standard. The original DBM API appeared in AT&T Research Unix
Version 7, and only allowed access to a single file at a time.
There are many different implementations of this API, including:
· The original BSD 4.3 ndbm, based on AT&T dbm. Found in commer‐
cial Un*x offerings.
· Berkeley DB v1 compatibility interface. Supplied with 4.4BSD
based systems: (Free|Open|Net)BSD, MacOS X.
· GNU DBM (GDBM) found in Linux distributions.
· SDBM, Ozan Yigit's Public Domain implementation of NDBM. Sup‐
plied with this distribution, and used as a last resort on Un*x
systems (and by default on non Un*x systems).
DBM_OPEN takes a filename (STRING), flags (either "R" for read-only,
"W" for write access, or "CW" to create and write a new file), and a
"mode" string, which defaults to "0660" (octal) and returns a database
handle which can be passed to the remaining functions.
DBM_CLOSE closes the database file. DBM_CLOSE MUST be called to ensure
that all your data is written.
DBM_STORE takes a database handle, key and datum strings, and a flag
(either DBM_INSERT to insert a new pair, or fail if the key already
exists, or DBM_REPLACE to insert or replace existing data). The key
and datum strings may contain an arbitrary series of characters.
DBM_FETCH returns the stored datum (if any) for the supplied key, or
fails.
DBM_DELETE deletes the stored datum (if any) for the supplied key, or
fails.
DBM_FIRSTKEY and subsequent calls to DBM_NEXTKEY allow you to traverse
all stored keys. The keys will be returned in arbitrary order, and the
routines will fail at the end of the traversal.
DBM_ERROR is a predicate which succeeds if the database handle is valid
and an I/O error has occurred on the file. DBM_CLEARERR is a predicate
which succeeds if if the database handle is valid, and has the side
effect of clearing the I/O error flag.
FILES
NDBM, GDBM, and SDBM create two files: filename.dir, filename.pag.
Berkeley DB creates a single filename.db file.
SEE ALSOndbm(3), dbopen(3), gdbm(3).
AUTHOR
Philip L. Budne
BUGS
None of the implementations allow concurrent read and write.
Some implementations (classic NDBM and SDBM) place limits on the total
size of key plus datum (typically slightly less than 1KB).
NOTE: Some implementations (classic NDBM and SDBM) create sparse file
which appear (to "ls -l") to be larger than they are (see "ls -s").
Copying such files may cause the non-allocated blocks to be "filled"
with zeroed disk blocks, and then the files really will be large!
Only GDBM provides locking to eliminate the possibility of file corrup‐
tion, or reading of incomplete data.
GDBM locking sometimes fails on NFS mounted partitions (particularly on
Linux systems). GDBM's NDBM interface does not provide a way to dis‐
able locking.
DBM databases accessed concurrently by multiple processes are tradi‐
tionally (re)created from text files and used for fast disk-based read-
only table lookups. Programs which need to update the file generate a
new temporary copy using a different name, and then rename the new
file(s), so that the next reader gets the new copies (existing readers
continue to see old data).
SNOBOL 3 Dec 2005 SNOBOL4DBM(1)
