Using MySQL Programs

This chapter is from the book

MySQL Administrator's Guide

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This chapter is from the book

This chapter is from the book 

MySQL Administrator's Guide

Learn More Buy

3.3 Specifying Program Options

You can provide options for MySQL programs in several ways:

• On the command line following the program name. This is most common for options that apply to a specific invocation of the program.

• In an option file that the program reads when it starts. This is common for options that you want the program to use each time it runs.

• In environment variables. These are useful for options that you want to apply each time the program runs, although in practice option files are used more commonly for this purpose. (Section 4.9.2, "Running Multiple Servers on Unix," discusses one situation in which environment variables can be very helpful. It describes a handy technique that uses such variables to specify the TCP/IP port number and Unix socket file for both the server and client programs.)

MySQL programs determine which options are given first by examining environment variables, then option files, and then the command line. If an option is specified multiple times, the last occurrence takes precedence. This means that environment variables have the lowest precedence and command-line options the highest.

You can take advantage of the way that MySQL programs process options by specifying the default values for a program's options in an option file. Then you need not type them each time you run the program, but can override the defaults if necessary by using command-line options.

3.3.1 Using Options on the Command Line

Program options specified on the command line follow these rules:

• Options are given after the command name.

• An option argument begins with one dash or two dashes, depending on whether it has a short name or a long name. Many options have both forms. For example, -? and --help are the short and long forms of the option that instructs a MySQL program to display a help message.

• Option names are case sensitive. -v and -V are both legal and have different meanings. (They are the corresponding short forms of the --verbose and --version options.)

• Some options take a value following the option name. For example, -h localhost and --host=localhost indicate the MySQL server host to a client program. The option value tells the program the name of the host where the MySQL server is running.

• For a long option that takes a value, separate the option name and the value by an '=' sign. For a short option that takes a value, the option value can immediately follow the option letter, or there can be a space between. (-hlocalhost and -h localhost are equivalent.) An exception to this rule is the option for specifying your MySQL password. This option can be given in long form as --password=pass_val or as --password. In the latter case (with no password value given), the program will prompt you for the password. The password option also may be given in short form as -ppass_val or as -p. However, for the short form, if the password value is given, it must follow the option letter with no intervening space. The reason for this is that if a space follows the option letter, the program has no way to tell whether a following argument is supposed to be the password value or some other kind of argument. Consequently, the following two commands have two completely different meanings:

shell> mysql -ptest
shell> mysql -p test

• The first command instructs mysql to use a password value of test, but specifies no default database. The second instructs mysql to prompt for the password value and to use test as the default database.

MySQL 4.0 introduced some additional flexibility in the way you specify options. These changes were made in MySQL 4.0.2. Some of them relate to the way you specify options that have "enabled" and "disabled" states, and to the use of options that might be present in one version of MySQL but not another. Those capabilities are discussed in this section. Another change pertains to the way you use options to set program variables. Section 3.3.4, "Using Options to Set Program Variables," discusses that topic further.

Some options control behavior that can be turned on or off. For example, the mysql client supports a --column-names option that determines whether or not to display a row of column names at the beginning of query results. By default, this option is enabled. However, you may want to disable it in some instances, such as when sending the output of mysql into another program that expects to see only data and not an initial header line.

To disable column names, you can specify the option using any of these forms:

--disable-column-names
--skip-column-names
--column-names=0

The --disable and --skip prefixes and the =0 suffix all have the same effect: They turn the option off.

The "enabled" form of the option may be specified in any of these ways:

--column-names
--enable-column-names
--column-names=1

Another change to option processing introduced in MySQL 4.0 is that you can use the --loose prefix for command-line options. If an option is prefixed by --loose, the program will not exit with an error if it does not recognize the option, but instead will issue only a warning:

shell> mysql --loose-no-such-option
mysql: WARNING: unknown option '--no-such-option'

The --loose prefix can be useful when you run programs from multiple installations of MySQL on the same machine, at least if all the versions are as recent as 4.0.2. This prefix is particularly useful when you list options in an option file. An option that may not be recognized by all versions of a program can be given using the --loose prefix (or loose in an option file). Versions of the program that do not recognize the option will issue a warning and ignore it. This strategy requires that versions involved be 4.0.2 or later, because earlier versions know nothing of the --loose convention.

3.3.2 Using Option Files

MySQL programs can read startup options from option files (also sometimes called "configuration files"). Option files provide a convenient way to specify commonly used options so that they need not be entered on the command line each time you run a program. Option file capability is available from MySQL 3.22 on.

The following programs support option files: myisamchk, myisampack, mysql, mysql.server, mysqladmin, mysqlbinlog, mysqlcc, mysqlcheck, mysqld, mysqld_safe, mysqldump, mysqlhotcopy, mysqlimport, and mysqlshow.

On Windows, MySQL programs read startup options from the following files:

WINDIR represents the location of your Windows directory. This is commonly C:\Windows or C:\WinNT. You can determine its exact location from the value of the WINDIR environment variable using the following command:

C:\> echo %WINDIR%

On Unix, MySQL programs read startup options from the following files:

DATADIR represents the location of the MySQL data directory. Typically this is /usr/local/mysql/data for a binary installation or /usr/local/var for a source installation. Note that this is the data directory location that was specified at configuration time, not the one specified with --datadir when mysqld starts. Use of --datadir at runtime has no effect on where the server looks for option files, because it looks for them before processing any command-line arguments.

MySQL looks for option files in the order just described and reads any that exist. If multiple option files exist, an option specified in a file read later takes precedence over the same option specified in a file read earlier.

Any long option that may be given on the command line when running a MySQL program can be given in an option file as well. To get the list of available options for a program, run it with the --help option.

The syntax for specifying options in an option file is similar to command-line syntax, except that you omit the leading two dashes. For example, --quick or --host=localhost on the command line should be specified as quick or host=localhost in an option file. To specify an option of the form --loose-opt_name in an option file, write it as loose-opt_name.

Empty lines in option files are ignored. Non-empty lines can take any of the following forms:

• #comment

;comment

Comment lines start with '#' or ';'. As of MySQL 4.0.14, a '#'-comment can start in the middle of a line as well.

• [group]

group is the name of the program or group for which you want to set options. After a group line, any opt_name or set-variable lines apply to the named group until the end of the option file or another group line is given.

• opt_name

This is equivalent to --opt_name on the command line.

• opt_name=value

This is equivalent to --opt_name=value on the command line. In an option file, you can have spaces around the '=' character, something that is not true on the command line. As of MySQL 4.0.16, you can quote the value with double quotes or single quotes. This is useful if the value contains a '#' comment character or whitespace.

• set-variable = var_name=value

Set the program variable var_name to the given value. This is equivalent to --set- variable=var_name=value on the command line. Spaces are allowed around the first '=' character but not around the second. This syntax is deprecated as of MySQL 4.0. See Section 3.3.4, "Using Options to Set Program Variables," for more information on setting program variables.

Leading and trailing blanks are automatically deleted from option names and values. You may use the escape sequences '\b', '\t', '\n', '\r', '\\', and '\s' in option values to represent the backspace, tab, newline, carriage return, and space characters.

On Windows, if an option value represents a pathname, you should specify the value using '/' rather than '\' as the pathname separator. If you use '\', you must double it as '\\', because '\' is the escape character in MySQL.

If an option group name is the same as a program name, options in the group apply specifically to that program.

The [client] option group is read by all client programs (but not by mysqld). This allows you to specify options that apply to every client. For example, [client] is the perfect group to use to specify the password that you use to connect to the server. (But make sure that the option file is readable and writable only by yourself, so that other people cannot find out your password.) Be sure not to put an option in the [client] group unless it is recognized by all client programs that you use. Programs that do not understand the option will quit after displaying an error message if you try to run them.

As of MySQL 4.0.14, if you want to create option groups that should be read by only one specific mysqld server release series, you can do this by using groups with names of [mysqld-4.0], [mysqld-4.1], and so forth. The following group indicates that the --new option should be used only by MySQL servers with 4.0.x version numbers:

[mysqld-4.0]
new

Here is a typical global option file:

[client]
port=3306
socket=/tmp/mysql.sock


[mysqld]
port=3306
socket=/tmp/mysql.sock
key_buffer_size=16M
max_allowed_packet=8M


[mysqldump]
quick

The preceding option file uses var_name=value syntax for the lines that set the key_buffer_size and max_allowed_packet variables. Prior to MySQL 4.0.2, you would need to use set-variable syntax instead (described earlier in this section).

Here is a typical user option file:

[client]
# The following password will be sent to all standard MySQL clients
password="my_password"

[mysql]
no-auto-rehash
set-variable = connect_timeout=2

[mysqlhotcopy]
interactive-timeout

This option file uses set-variable syntax to set the connect_timeout variable. For MySQL 4.0.2 and up, you can also set the variable using just connect_timeout=2.

If you have a source distribution, you will find sample option files named my-xxxx.cnf in the support-files directory. If you have a binary distribution, look in the support-files directory under your MySQL installation directory (typically C:\mysql on Windows or /usr/local/mysql on Unix). Currently there are sample option files for small, medium, large, and very large systems. To experiment with one of these files, copy it to C:\my.cnf on Windows or to .my.cnf in your home directory on Unix.

Note: On Windows, the .cnf option file extension might not be displayed.

All MySQL programs that support option files handle the following command-line options:

• --no-defaults

Don't read any option files.

• --print-defaults

Print the program name and all options that it will get from option files.

• --defaults-file=path_name

Use only the given option file. path_name is the full pathname to the file.

• --defaults-extra-file=path_name

Read this option file after the global option file but before the user option file. path_name is the full pathname to the file.

To work properly, each of these options must immediately follow the command name on the command line, with the exception that --print-defaults may be used immediately after --defaults-file or --defaults-extra-file.

In shell scripts, you can use the my_print_defaults program to parse option files. The following example shows the output that my_print_defaults might produce when asked to show the options found in the [client] and [mysql] groups:

shell> my_print_defaults client mysql
--port=3306
--socket=/tmp/mysql.sock
--no-auto-rehash

Note for developers: Option file handling is implemented in the C client library simply by processing all matching options (that is, options in the appropriate group) before any command-line arguments. This works nicely for programs that use the last instance of an option that is specified multiple times. If you have a C or C++ program that handles multiply specified options this way but doesn't read option files, you need add only two lines to give it that capability. Check the source code of any of the standard MySQL clients to see how to do this.

Several other language interfaces to MySQL are based on the C client library, and some of them provide a way to access option file contents. These include Perl and Python. See the documentation for your preferred interface for details.

3.3.3 Using Environment Variables to Specify Options

To specify an option using an environment variable, set the variable using the syntax appropriate for your comment processor. For example, on Windows or NetWare, you can set the USER variable to specify your MySQL account name. To do so, use this syntax:

SET USER=your_name

The syntax on Unix depends on your shell. Suppose that you want to specify the TCP/IP port number using the MYSQL_TCP_PORT variable. The syntax for Bourne shell and variants (sh, bash, zsh, and so on) is:

MYSQL_TCP_PORT=3306

For csh and tcsh, use this syntax:

setenv MYSQL_TCP_PORT 3306

The commands to set environment variables can be executed at your command prompt to take effect immediately. These settings persist until you log out. To have the settings take effect each time you log in, place the appropriate command or commands in a startup file that your command interpreter reads each time it starts. Typical startup files are AUTOEXEC.BAT for Windows, .bash_profile for bash, or .tcshrc for tcsh. Consult the documentation for your command interpreter for specific details.

Appendix B, "Environment Variables," lists all environment variables that affect MySQL program operation.

3.3.4 Using Options to Set Program Variables

Many MySQL programs have internal variables that can be set at runtime. As of MySQL 4.0.2, program variables are set the same way as any other long option that takes a value. For example, mysql has a max_allowed_packet variable that controls the maximum size of its communication buffer. To set the max_allowed_packet variable for mysql to a value of 16MB, use either of the following commands:

shell> mysql --max_allowed_packet=16777216
shell> mysql --max_allowed_packet=16M

The first command specifies the value in bytes. The second specifies the value in megabytes. Variable values can have a suffix of K, M, or G (either uppercase or lowercase) to indicate units of kilobytes, megabytes, or gigabytes, respectively.

In an option file, the variable setting is given without the leading dashes:

[mysql]
max_allowed_packet=16777216

Or:

[mysql]
max_allowed_packet=16M

If you like, underscores in a variable name can be specified as dashes.

Prior to MySQL 4.0.2, program variable names are not recognized as option names. Instead, use the --set-variable option to assign a value to a variable:

shell> mysql --set-variable=max_allowed_packet=16777216
shell> mysql --set-variable=max_allowed_packet=16M

In an option file, omit the leading dashes:

[mysql]
set-variable = max_allowed_packet=16777216

Or:

[mysql]
set-variable = max_allowed_packet=16M

With --set-variable, underscores in variable names cannot be given as dashes for versions of MySQL older than 4.0.2.

The --set-variable option is still recognized in MySQL 4.0.2 and up, but is deprecated.

Some server variables can be set at runtime. For details, see Section 4.2.3.1.2, "Dynamic System Variables."