gdbmtool - examine and modify a GDBM database



gdbmtool − examine and modify a GDBM database


gdbmtool [−lmNnqrs] [−b SIZE] [−c SIZE] [−f FILE] [−−block−size=SIZE] [−−cache−size=SIZE] [−−file FILE] [−−newdb] [−−no−lock] [−−no−mmap] [−−norc] [−−quiet] [−−read−only] [−−synchronize] [DBFILE] [COMMAND [; COMMAND...]]

gdbmtool [−Vh] [−−help] [−−usage] [−−version]


The gdbmtool utility allows you to view and modify an existing GDBM database or to create a new one.

The DBFILE argument supplies the name of the database to open. If not supplied, the default name junk.gdbm is used instead. If the named database does not exist, it will be created. An existing database can be cleared (i.e. all records removed from it) using the −−newdb option (see below).

Unless the −N (−−norc) option is given, after startup gdbmtool looks for file named .gdbmtoolrc first in the current working directory, and, if not found there, in the home directory of the user who started the program. If found, this file is read and interpreted as a list of gdbmtool commands.

Then gdbmtool starts a loop, in which it reads commands from the standard input, executes them and prints the results on the standard output. If the standard input is attached to a console, the program runs in interactive mode.

The program terminates when the quit command is given, or end-of-file is detected on its standard input.

Commands can also be specified in the command line, after the DBFILE argument. In this case, they will be interpreted without attempting to read more commands from the standard input.

If several commands are supplied, they must be separated by semicolons (properly escaped or quoted, in order to prevent them from being interpreted by the shell).

A gdbmtool command consists of a command verb, optionally followed by one or more arguments, separated by any amount of white space. A command verb can be entered either in full or in an abbreviated form, as long as that abbreviation does not match any other verb.

Any sequence of non-whitespace characters appearing after the command verb forms an argument. If the argument contains whitespace or unprintable characters it must be enclosed in double quotes. Within double quotes the usual escape sequences are understood, as shown in the table below:




Audible bell character (ASCII 7)


Backspace character (ASCII 8)


Form-feed character (ASCII 12)


Newline character (ASCII 10)


Carriage return character (ASCII 13)


Horizontal tabulation character (ASCII 9)


Vertical tabulation character (ASCII 11)


Single slash

In addition, a backslash immediately followed by the end-of-line character effectively removes that character, allowing to split long arguments over several input lines.


−b, −−block−size=SIZE

Set block size.

−c, −−cache−size=SIZE

Set cache size.

−f, −−file=FILE

Read commands from FILE, instead of from the standard input.

−l, −−no−lock

Disable file locking.

−m, −−no−mmap

Do not use mmap(2).

−n, −−newdb

Create the database, truncating it if it already exists.

−q, −−quiet

Don’t print initial banner.

−r, −−read−only

Open database in read-only mode.

−s, −−synchronize

Synchronize to disk after each write.

−h, −−help

Print a short usage summary.


Print a list of available options.

−V, −−version

Print program version



Print the avail list.

bucket NUM

Print the bucket number NUM and set is as the current one.


Print the bucket cache.


Close the currently open database.


Print the number of entries in the database.


Print the current bucket.

delete KEY

Delete record with the given KEY.


Print hash directory.


Downgrade the database from the extended numsync format to the standard format.

export FILE−NAME [truncate] [binary|ascii]

Export the database to the flat file FILE−NAME. This is equivalent to gdbm_dump(1).

This command will not overwrite an existing file, unless the truncate parameter is also given. Another optional parameter determines the type of the dump (*note Flat files::). By default, ASCII dump will be created.

fetch KEY

Fetch and display the record with the given KEY.


Fetch and display the first record in the database. Subsequent records can be fetched using the next command (see below).

hash KEY

Compute and display the hash value for the given KEY.


Print file header.

help or ?

Print a concise command summary, showing each command letter and verb with its parameters and a short description of what it does. Optional arguments are enclosed in square brackets.


Shows the command history list with line numbers. This command is available only if the program was compiled with GNU Readline.

history COUNT.

Shows COUNT latest commands from the command history.

history N COUNT.

Shows COUNT commands from the command history starting with Nth command.

import FILE−NAME [replace] [nometa]

Import data from a flat dump file FILE−NAME. If the replace argument is given, any records with the same keys as the already existing ones will replace them. The nometa argument turns off restoring meta-information from the dump file.


List the contents of the database.

next [KEY]

Sequential access: fetch and display the next record. If the KEY is given, the record following the one with this key will be fetched.

open FILE

Open the database file FILE. If successful, any previously open database is closed. Otherwise, if the operation fails, the currently opened database remains unchanged.

This command takes additional information from the variables open, lock, mmap, and sync. See the section VARIABLES, for a detailed description of these.


Close the database and quit the utility.


Reorganize the database.

set [VAR=VALUE...]

Without arguments, lists variables and their values. If arguments are specified, sets variables. Boolean variables can be set by specifying variable name, optionally prefixed with no, to set it to false.

snapshot FILE FILE

Analyzes two database snapshots and selects the most recent of them. In case of error, prints a detailed diagnostics. Use this command to manually recover from a crash. For details, please refer to the chapter Crash Tolerance in the GDBM manual.

source FILE

Read commands from the given FILE.


Print current program status.

store KEY DATA

Store the DATA with the given KEY in the database. If the KEY already exists, its data will be replaced.


Synchronize the database file with the disk storage.


Upgrade the database from the standard to the extended numsync format.

unset VARIABLE...

Unsets listed variables.


Print the version of gdbm.


The define statement provides a mechanism for defining key or content structures. It is similar to the C struct declaration:

define key|content { defnlist }

The defnlist is a comma-separated list of member declarations. Within defnlist the newline character looses its special meaning as the command terminator, so each declaration can appear on a separate line and arbitrary number of comments can be inserted to document the definition.

Each declaration has one of the following formats

type name
type name

where type is a data type and name is the member name. The second format defines the member name as an array of N elements of type.

The supported types are:




single byte (signed)


signed short integer


unsigned short integer


signed integer


unsigned integer




signed long integer


unsigned long integer


signed long long integer


unsigned long long integer


a floating point number


double-precision floating point number


array of characters (see the NOTE below)


null-terminated string of characters

The following alignment declarations can be used within defnlist:

The next member begins at offset N.

pad N

Add N bytes of padding to the previous member.

For example:

define content {
int status,
pad 8,
char id[3],
stringz name

To define data consisting of a single data member, the following simplified construct can be used:

define key|content type

where type is one of the types discussed above.

NOTE: The string type can reasonably be used only if it is the last or the only member of the data structure. That’s because it provides no information about the number of elements in the array, so it is interpreted to contain all bytes up to the end of the datum.


confirm, boolean

Whether to ask for confirmation before certain destructive operations, such as truncating the existing database. Default is true.

ps1, string

Primary prompt string. Its value can contain conversion specifiers, consisting of the % character followed by another character. These specifiers are expanded in the resulting prompt as follows:

Sequence Expansion


name of the db file


program name


package name (gdbm)


horizontal space (ASCII 32)


program version



The default prompt is %p>%_.

ps2, string

Secondary prompt. See ps1 for a description of its value. This prompt is displayed before reading the second and subsequent lines of a multi-line command.

The default value is %_>%_.

delim1, string

A string used to delimit fields of a structured datum on output (see the section DATA DEFINITIONS).

Default is , (a comma). This variable cannot be unset.

delim2, string

A string used to delimit array items when printing a structured datum.

Default is , (a comma). This variable cannot be unset.

pager, string

The name and command line of the pager program to pipe output to. This program is used in interactive mode when the estimated number of output lines is greater then the number of lines on your screen.

The default value is inherited from the environment variable PAGER. Unsetting this variable disables paging.

quiet, boolean

Whether to display welcome banner at startup. This variable should be set in a startup script file.

The following variables control how the database is opened:
, numeric

Sets the cache size. By default this variable is not set.

blocksize, numeric

Sets the block size. Unset by default.

open, string

Open mode. The following values are allowed:


Truncate the database if it exists or create a new one. Open it in read-write mode.

wrcreat or rw

Open the database in read-write mode. Create it if it does not exist. This is the default.

reader or readonly

Open the database in read-only mode. Signal an error if it does not exist.

filemode, octal

Sets the file mode for newly created database files. Default is 0644.

lock, boolean

Lock the database. This is the default.

mmap, boolean

Use memory mapping. This is the default.

coalesce, boolean

When set, this option causes adjacent free blocks to be merged which allows for more efficient memory management at the expense of a certain increase in CPU usage.

centfree, boolean

Enables central free block pool. This causes all free blocks of space to be placed in the global pool, thereby speeding up the allocation of data space.


gdbm_dump(1), gdbm_load(1), gdbm(3).


Report bugs to <bug−[email protected]>.


Copyright © 2013-2021 Free Software Foundation, Inc
License GPLv3+: GNU GPL version 3 or later <>
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

Updated 2024-01-29 - |