Chapter 41. Specifying Program Options

Table of Contents

Using Options on the Command Line
Using Option Files
Using Environment Variables to Specify Options
Using Options to Set Program Variables

You can provide options for MySQL programs in several ways:

MySQL programs determine which options are given by examining environment variables first, then option files, 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 value 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.

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 or --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 may be present in one version of MySQL but not another. Those capabilities are discussed here. Another change pertains to the way you use options to set program variables. 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 of turning the option off.

The ``enabled'' form of the option may be specified as:

--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 only issue 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. Note that this strategy works only if all versions involved are 4.0.2 or later, because earlier versions know nothing of the --loose convention.