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PSQL !!!PSQL NAME SYNOPSIS DESCRIPTION PSQL META-COMMANDS COMMAND-LINE OPTIONS ADVANCED FEATURES EXAMPLES APPENDIX ---- !!NAME psql - PostgreSQL interactive terminal !!SYNOPSIS psql [[ ''options'' ] [[ ''dbname'' [[ ''user'' ] ] __SUMMARY__ __psql__ is a terminal-based front-end to PostgreSQL. It enables you to type in queries interactively, issue them to PostgreSQL, and see the query results. Alternatively, input can be from a file. In addition, it provides a number of meta-commands and various shell-like features to facilitate writing scripts and automating a wide variety of tasks. !!DESCRIPTION __CONNECTING TO A DATABASE__ __psql__ is a regular PostgreSQL client application. In order to connect to a database you need to know the name of your target database, the hostname and port number of the server and what user name you want to connect as. __psql__ can be told about those parameters via command line options, namely __-d__, __-h__, __-p__, and __-U__ respectively. If an argument is found that does not belong to any option it will be interpreted as the database name (or the user name, if the database name is also given). Not all these options are required, defaults do apply. If you omit the host name psql will connect via a Unix domain socket to a server on the local host. The default port number is compile-time determined. Since the database server uses the same default, you will not have to specify the port in most cases. The default user name is your Unix username, as is the default database name. Note that you can't just connect to any database under any username. Your database administrator should have informed you about your access rights. To save you some typing you can also set the environment variables __PGDATABASE__, __PGHOST__, __PGPORT__ and __PGUSER__ to appropriate values. If the connection could not be made for any reason (e.g., insufficient privileges, postmaster is not running on the server, etc.), __psql__ will return an error and terminate. __ENTERING QUERIES__ In normal operation, __psql__ provides a prompt with the name of the database to which __psql__ is currently connected, followed by the string = __ $ __psql testdb __Welcome to psql, the PostgreSQL interactive terminal. Type: copyright for distribution terms h for help with SQL commands ? for help on internal slash commands g or terminate with semicolon to execute query q to quit testdb= __At the prompt, the user may type in SQL queries. Ordinarily, input lines are sent to the backend when a query-terminating semicolon is reached. An end of line does not terminate a query! Thus queries can be spread over several lines for clarity. If the query was sent and without error, the query results are displayed on the screen. Whenever a query is executed, __psql__ also polls for asynchronous notification events generated by LISTEN [[__listen__(l)] and NOTIFY [[__notify__(l)]. !!PSQL META-COMMANDS Anything you enter in __psql__ that begins with an unquoted backslash is a __psql__ meta-command that is processed by __psql__ itself. These commands are what makes __psql__ interesting for administration or scripting. Meta-commands are more commonly called slash or backslash commands. The format of a __psql__ command is the backslash, followed immediately by a command verb, then any arguments. The arguments are separated from the command verb and each other by any number of whitespace characters. To include whitespace into an argument you must quote it with a single quote. To include a single quote into such an argument, precede it by a backslash. Anything contained in single quotes is furthermore subject to C-like substitutions for n (new line), t (tab), \''digits'', 0''digits'', and 0x''digits'' (the character with the given decimal, octal, or hexadecimal code). If an unquoted argument begins with a colon (:), it is taken as a variable and the value of the variable is taken as the argument instead. Arguments that are quoted in ``backticks'' (`) are taken as a command line that is passed to the shell. The output of the command (with a trailing newline removed) is taken as the argument value. The above escape sequences also apply in backticks. Some commands take the name of an SQL identifier (such as a table name) as argument. These arguments follow the syntax rules of SQL regarding double quotes: an identifier without double quotes is coerced to lower-case. For all other commands double quotes are not special and will become part of the argument. Parsing for arguments stops when another unquoted backslash occurs. This is taken as the beginning of a new meta-command. The special sequence \ (two backslashes) marks the end of arguments and continues parsing SQL queries, if any. That way SQL and __psql__ commands can be freely mixed on a line. But in any case, the arguments of a meta-command cannot continue beyond the end of the line. The following meta-commands are defined: __a__ If the current table output format is unaligned, switch to aligned. If it is not unaligned, set it to unaligned. This command is kept for backwards compatibility. See __pset__ for a general solution. __cd [[__''directory''__]__ Change the current working directory to ''directory''. Without argument, change to the current user's home directory. __Tip:__ To print your current working directory, use !pwd. __C [[__ ''title'' __]__ Set the title of any tables being printed as the result of a query or unset any such title. This command is equivalent to pset title ''title''. (The name of this command derives from ``caption'', as it was previously only used to set the caption in an HTML table.) __connect (or c) [[__ ''dbname'' __[[__ ''username'' __] ]__ Establishes a connection to a new database and/or under a user name. The previous connection is closed. If ''dbname'' is - the current database name is assumed. If ''username'' is omitted the current user name is assumed. As a special rule, __connect__ without any arguments will connect to the default database as the default user (as you would have gotten by starting __psql__ without any arguments). If the connection attempt failed (wrong username, access denied, etc.), the previous connection will be kept if and only if __psql__ is in interactive mode. When executing a non-interactive script, processing will immediately stop with an error. This distinction was chosen as a user convenience against typos on the one hand, and a safety mechanism that scripts are not accidentally acting on the wrong database on the other hand. __copy__ ''table'' Performs a frontend (client) copy. This is an operation that runs an SQL COPY [[__copy__(l)] command, but instead of the backend's reading or writing the specified file, and consequently requiring backend access and special user privilege, as well as being bound to the file system accessible by the backend, __psql__ reads or writes the file and routes the data between the backend and the local file system. The syntax of the command is similar to that of the SQL __COPY__ command (see its description for the details). Note that, because of this, special parsing rules apply to the __copy__ command. In particular, the variable substitution rules and backslash escapes do not apply. __Tip:__ This operation is not as efficient as the SQL __COPY__ command because all data must pass through the client/server IP or socket connection. For large amounts of data the other technique may be preferable. __Note:__ Note the difference in interpretation of stdin and stdout between frontend and backend copies: in a frontend copy these always refer to __psql__'s input and output stream. On a backend copy stdin comes from wherever the __COPY__ itself came from (for example, a script run with the __-f__ option), and stdout refers to the query output stream (see __o__ meta-command below). __copyright__ Shows the copyright and distribution terms of __PostgreSQL__. __d__ ''relation'' Shows all columns of ''relation'' (which could be a table, view, index, or sequence), their types, and any special attributes such as NOT NULL or defaults, if any. If the relation is, in fact, a table, any defined indices, primary keys, unique constraints and check constraints are also listed. If the relation is a view, the view definition is also shown. The command form d+ is identical, but any comments associated with the table columns are shown as well. __Note:__ If __d__ is called without any arguments, it is equivalent to __dtvs__ which will show a list of all tables, views, and sequences. This is purely a convenience measure. __da [[__ ''pattern'' __]__ Lists all available aggregate functions, together with the data type they operate on. If ''pattern'' (a regular expression) is specified, only matching aggregates are shown. __dd [[__ ''object'' __]__ Shows the descriptions of ''object'' (which can be a regular expression), or of all objects if no argument is given. (``Object'' covers aggregates, functions, operators, types, relations (tables, views, indexes, sequences, large objects), rules, and triggers.) For example: =dd version __ Object descriptions Name | What | Description ---------+----------+--------------------------- version | function | PostgreSQL version string (1 row) Descriptions for objects can be generated with the __COMMENT ON__ SQL command. __Note:__ PostgreSQL stores the object descriptions in the pg_description system table. __df [[__ ''pattern'' __]__ Lists available functions, together with their argument and return types. If ''pattern'' (a regular expression) is specified, only matching functions are shown. If the form df+ is used, additional information about each function, including language and description, is shown. __distvS [[__ ''pattern'' __]__ This is not the actual command name: The letters i, s, t, v, S stand for index, sequence, table, view, and system table, respectively. You can specify any or all of them in any order to obtain a listing of them, together with who the owner is. If ''pattern'' is specified, it is a regular expression that restricts the listing to those objects whose name matches. If one appends a ``+'' to the command name, each object is listed with its associated description, if any. __dl__ This is an alias for __lo_list__, which shows a list of large objects. __do [[__ ''name'' __]__ Lists available operators with their operand and return types. If ''name'' is specified, only operators with that name will be shown. __dp [[__ ''pattern'' __]__ This is an alias for __z__ which was included for its greater mnemonic value (``display permissions''). __dT [[__ ''pattern'' __]__ Lists all data types or only those that match ''pattern''. The command form dT+ shows extra information. __du [[__ ''pattern'' __]__ Lists all configured users or only those that match ''pattern''. __edit (or e) [[__ ''filename'' __]__ If ''filename'' is specified, the file is edited; after the editor exits, its content is copied back to the query buffer. If no argument is given, the current query buffer is copied to a temporary file which is then edited in the same fashion. The new query buffer is then re-parsed according to the normal rules of __psql__, where the whole buffer is treated as a single line. (Thus you cannot make scripts this way. Use __i__ for that.) This means also that if the query ends with (or rather contains) a semicolon, it is immediately executed. In other cases it will merely wait in the query buffer. __Tip: psql__ searches the environment variables __PSQL_EDITOR__, __EDITOR__, and __VISUAL__ (in that order) for an editor to use. If all of them are unset, ''/bin/vi'' is run. __echo__ ''text'' __[[ ... ]__ Prints the arguments to the standard output, separated by one space and followed by a newline. This can be useful to intersperse information in the output of scripts. For example: =echo `date` __Tue Oct 26 21:40:57 CEST 1999 If the first argument is an unquoted -n the the trailing newline is not written. __Tip:__ If you use the __o__ command to redirect your query output you may wish to use __qecho__ instead of this command. __encoding [[__ ''encoding'' __]__ Sets the client encoding, if you are using multibyte encodings. Without an argument, this command shows the current encoding. __f [[__ ''string'' __]__ Sets the field separator for unaligned query output. The default is pipe (|). See also __pset__ for a generic way of setting output options. __g [[ {__ ''filename'' __| |__''command'' __} ]__ Sends the current query input buffer to the backend and optionally saves the output in ''filename'' or pipes the output into a separate Unix shell to execute ''command''. A bare g is virtually equivalent to a semicolon. A g with argument is a ``one-shot'' alternative to the __o__ command. __help (or h) [[__ ''command'' __]__ Give syntax help on the specified SQL command. If ''command'' is not specified, then __psql__ will list all the commands for which syntax help is available. If ''command'' is an asterisk (``*''), then syntax help on all SQL commands is shown. __Note:__ To simplify typing, commands that consists of several words do not have to be quoted. Thus it is fine to type __help alter table__. __H__ Turns on HTML query output format. If the HTML format is already on, it is switched back to the default aligned text format. This command is for compatibility and convenience, but see __pset__ about setting other output options. __i__ ''filename'' Reads input from the file ''filename'' and executes it as though it had been typed on the keyboard. __Note:__ If you want to see the lines on the screen as they are read you must set the variable __ECHO__ to all. __l (or list)__ List all the databases in the server as well as their owners. Append a ``+'' to the command name to see any descriptions for the databases as well. If your PostgreSQL installation was compiled with multibyte encoding support, the encoding scheme of each database is shown as well. __lo_export__ ''loid filename'' Reads the large object with OID ''loid'' from the database and writes it to ''filename''. Note that this is subtly different from the server function __lo_export__, which acts with the permissions of the user that the database server runs as and on the server's file system. __Tip:__ Use __lo_list__ to find out the large object's OID. __Note:__ See the description of the __LO_TRANSACTION__ variable for important information concerning all large object operations. __lo_import__ ''filename'' __[[__ ''comment'' __]__ Stores the file into a PostgreSQL ``large object''. Optionally, it associates the given comment with the object. Example: foo=lo_import '/home/peter/pictures/photo.xcf' 'a picture of me' __lo_import 152801 The response indicates that the large object received object id 152801 which one ought to remember if one wants to access the object ever again. For that reason it is recommended to always associate a human-readable comment with every object. Those can then be seen with the __lo_list__ command. Note that this command is subtly different from the server-side __lo_import__ because it acts as the local user on the local file system, rather than the server's user and file system. __Note:__ See the description of the __LO_TRANSACTION__ variable for important information concerning all large object operations. __lo_list__ Shows a list of all PostgreSQL ``large objects'' currently stored in the database, along with any comments provided for them. __lo_unlink__ ''loid'' Deletes the large object with OID ''loid'' from the database. __Tip:__ Use __lo_list__ to find out the large object's OID. __Note:__ See the description of the __LO_TRANSACTION__ variable for important information concerning all large object operations. __o [[ {__''filename'' __| |__''command''__} ]__ Saves future query results to the file ''filename'' or pipes future results into a separate Unix shell to execute ''command''. If no arguments are specified, the query output will be reset to ''stdout''. ``Query results'' includes all tables, command responses, and notices obtained from the database server, as well as output of various backslash commands that query the database (such as __d__), but not error messages. __Tip:__ To intersperse text output in between query results, use __qecho__. __p__ Print the current query buffer to the standard output. __pset__ ''parameter'' __[[__ ''value'' __]__ This command sets options affecting the output of query result tables. ''parameter'' describes which option is to be set. The semantics of ''value'' depend thereon. Adjustable printing options are: __format__ Sets the output format to one of unaligned, aligned, html, or latex. Unique abbreviations are allowed. (That would mean one letter is enough.) ``Unaligned'' writes all fields of a tuple on a line, separated by the currently active field separator. This is intended to create output that might be intended to be read in by other programs (tab-separated, comma-separated). ``Aligned'' mode is the standard, human-readable, nicely formatted text output that is default. The ``HTML'' and ``LaTeX'' modes put out tables that are intended to be included in documents using the respective mark-up language. They are not complete documents! (This might not be so dramatic in HTML, but in LaTeX you must have a complete document wrapper.) __border__ The second argument must be a number. In general, the higher the number the more borders and lines the tables will have, but this depends on the particular format. In HTML mode, this will translate directly into the border=... attribute, in the others only values 0 (no border), 1 (internal dividing lines), and 2 (table frame) make sense. __expanded (or x)__ Toggles between regular and expanded format. When expanded format is enabled, all output has two columns with the field name on the left and the data on the right. This mode is useful if the data wouldn't fit on the screen in the normal ``horizontal'' mode. Expanded mode is supported by all four output modes. __null__ The second argument is a string that should be printed whenever a field is null. The default is not to print anything, which can easily be mistaken for, say, an empty string. Thus, one might choose to write pset null '(null)'. __fieldsep__ Specifies the field separator to be used in unaligned output mode. That way one can create, for example, tab- or comma-separated output, which other programs might prefer. To set a tab as field separator, type pset fieldsep 't'. The default field separator is '|' (a ``pipe'' symbol). __footer__ Toggles the display of the default footer (x rows). __recordsep__ Specifies the record (line) separator to use in unaligned output mode. The default is a newline character. __tuples_only (or t)__ Toggles between tuples only and full display. Full display may show extra information such as column headers, titles, and various footers. In tuples only mode, only actual table data is shown. __title [[__ ''text'' __]__ Sets the table title for any subsequently printed tables. This can be used to give your output descriptive tags. If no argument is given, the title is unset. __Note:__ This formerly only affected HTML mode. You can now set titles in any output format. __tableattr (or T) [[__ ''text'' __]__ Allows you to specify any attributes to be placed inside the HTML table tag. This could for example be cellpadding or bgcolor. Note that you probably don't want to specify border here, as that is already taken care of by pset border. __pager__ Toggles the list of a pager to do table output. If the environment variable __PAGER__ is set, the output is piped to the specified program. Otherwise ''more'' is used. In any case, __psql__ only uses the pager if it seems appropriate. That means among other things that the output is to a terminal and that the table would normally not fit on the screen. Because of the modular nature of the printing routines it is not always possible to predict the number of lines that will actually be printed. For that reason __psql__ might not appear very discriminating about when to use the pager and when not to. Illustrations on how these different formats look can be seen in the Examples [[psql(1)] section. __Tip:__ There are various shortcut commands for __pset__. See __a__, __C__, __H__, __t__, __T__, and __x__. __Note:__ It is an error to call __pset__ without arguments. In the future this call might show the current status of all printing options. __q__ Quit the __psql__ program. __qecho__ ''text'' __[[ ... ]__ This command is identical to __echo__ except that all output will be written to the query output channel, as set by __o__. __r__ Resets (clears) the query buffer. __s [[__ ''filename'' __]__ Print or save the command line history to ''filename''. If ''filename'' is omitted, the history is written to the standard output. This option is only available if __psql__ is configured to use the GNU history library. __Note:__ In the current version, it is no longer necessary to save the command history, since that will be done automatically on program termination. The history is also loaded automatically every time __psql__ starts up. __set [[__ ''name'' __[[__ ''value'' __[[ ... ]]]__ Sets the internal variable ''name'' to ''value'' or, if more than one value is given, to the concatenation of all of them. If no second argument is given, the variable is just set with no value. To unset a variable, use the __unset__ command. Valid variable names can contain characters, digits, and underscores. See the section about __psql__ variables for details. Although you are welcome to set any variable to anything you want, __psql__ treats several variables as special. They are documented in the section about variables. __Note:__ This command is totally separate from the SQL command SET [[__set__(l)]. __t__ Toggles the display of output column name headings and row count footer. This command is equivalent to pset tuples_only and is provided for convenience. __T__ ''table_options'' Allows you to specify options to be placed within the table tag in HTML tabular output mode. This command is equivalent to pset tableattr ''table_options''. __w {__''filename'' __|__ ''|command''__}__ Outputs the current query buffer to the file ''filename'' or pipes it to the Unix command ''command''. __x__ Toggles extended row format mode. As such it is equivalent to pset expanded. __z [[__ ''pattern'' __]__ Produces a list of all tables in the database with their appropriate access permissions listed. If an argument is given it is taken as a regular expression which limits the listing to those tables which match it. test=z __Access permissions for database __Read this as follows: SELECT__) permission on the table. UPDATE__, __DELETE__), ``append'' (__INSERT__) permissions, and permission to create rules on the table. SELECT__ and __INSERT__ permission. The commands __grant__(l) and __revoke__(l) are used to set access permissions. __! [[__ ''command'' __]__ Escapes to a separate Unix shell or executes the Unix command ''command''. The arguments are not further interpreted, the shell will see them as is. __?__ Get help information about the backslash (``'') commands. !!COMMAND-LINE OPTIONS If so configured, __psql__ understands both standard Unix short options, and GNU-style long options. The latter are not available on all systems. __-a, --echo-all__ Print all the lines to the screen as they are read. This is more useful for script processing rather than interactive mode. This is equivalent to setting the variable __ECHO__ to all. __-A, --no-align__ Switches to unaligned output mode. (The default output mode is otherwise aligned.) __-c, --command__ ''query'' Specifies that __psql__ is to execute one query string, ''query'', and then exit. This is useful in shell scripts. ''query'' must be either a query string that is completely parseable by the backend (i.e., it contains no __psql__ specific features), or it is a single backslash command. Thus you cannot mix SQL and __psql__ meta-commands. To achieve that, you could pipe the string into __psql__, like this: echo __ __-d, --dbname__ ''dbname'' Specifies the name of the database to connect to. This is equivalent to specifying ''dbname'' as the first non-option argument on the command line. __-e, --echo-queries__ Show all queries that are sent to the backend. This is equivalent to setting the variable __ECHO__ to queries. __-E, --echo-hidden__ Echoes the actual queries generated by d and other backslash commands. You can use this if you wish to include similar functionality into your own programs. This is equivalent to setting the variable __ECHO_HIDDEN__ from within __psql__. __-f, --file__ ''filename'' Use the file ''filename'' as the source of queries instead of reading queries interactively. After the file is processed, __psql__ terminates. This is in many ways equivalent to the internal command __i__. If ''filename'' is - (hyphen), then standard input is read. Using this option is subtly different from writing psql filename''. In general, both will do what you expect, but using -f enables some nice features such as error messages with line numbers. There is also a slight chance that using this option will reduce the start-up overhead. On the other hand, the variant using the shell's input redirection is (in theory) guaranteed to yield exactly the same output that you would have gotten had you entered everything by hand. __-F, --field-separator__ ''separator'' Use ''separator'' as the field separator. This is equivalent to __pset fieldsep__ or __f__. __-h, --host__ ''hostname'' Specifies the host name of the machine on which the __postmaster__ is running. If host begins with a slash, it is used as the directory for the unix domain socket. __-H, --html__ Turns on HTML tabular output. This is equivalent to pset format html or the __H__ command. __-l, --list__ Lists all available databases, then exits. Other non-connection options are ignored. This is similar to the internal command __list__. __-o, --output__ ''filename'' Put all query output into file ''filename''. This is equivalent to the command __o__. __-p, --port__ ''port'' Specifies the TCP/IP port or, by omission, the local Unix domain socket file extension on which the __postmaster__ is listening for connections. Defaults to the value of the __PGPORT__ environment variable or, if not set, to the port specified at compile time, usually 5432. __-P, --pset__ ''assignment'' Allows you to specify printing options in the style of __pset__ on the command line. Note that here you have to separate name and value with an equal sign instead of a space. Thus to set the output format to LaTeX, you could write -P format=latex. __-q__ Specifies that __psql__ should do its work quietly. By default, it prints welcome messages and various informational output. If this option is used, none of this happens. This is useful with the __-c__ option. Within __psql__ you can also set the __QUIET__ variable to achieve the same effect. __-R, --record-separator__ ''separator'' Use ''separator'' as the record separator. This is equivalent to the __pset recordsep__ command. __-s, --single-step__ Run in single-step mode. That means the user is prompted before each query is sent to the backend, with the option to cancel execution as well. Use this to debug scripts. __-S, --single-line__ Runs in single-line mode where a newline terminates a query, as a semicolon does. __Note:__ This mode is provided for those who insist on it, but you are not necessarily encouraged to use it. In particular, if you mix SQL and meta-commands on a line the order of execution might not always be clear to the inexperienced user. __-t, --tuples-only__ Turn off printing of column names and result row count footers, etc. It is completely equivalent to the __t__ meta-command. __-T, --table-attr__ ''table_options'' Allows you to specify options to be placed within the HTML table tag. See __pset__ for details. __-u__ Makes __psql__ prompt for the user name and password before connecting to the database. This option is deprecated, as it is conceptually flawed. (Prompting for a non-default user name and prompting for a password because the backend requires it are really two different things.) You are encouraged to look at the __-U__ and __-W__ options instead. __-U, --username__ ''username'' Connects to the database as the user ''username'' instead of the default. (You must have permission to do so, of course.) __-v, --variable, --set__ ''assignment'' Performs a variable assignment, like the __set__ internal command. Note that you must separate name and value, if any, by an equal sign on the command line. To unset a variable, leave off the equal sign. To just set a variable without a value, use the equal sign but leave off the value. These assignments are done during a very early stage of start-up, so variables reserved for internal purposes might get overwritten later. __-V, --version__ Shows the __psql__ version. __-W, --password__ Requests that __psql__ should prompt for a password before connecting to a database. This will remain set for the entire session, even if you change the database connection with the meta-command __connect__. In the current version, __psql__ automatically issues a password prompt whenever the backend requests password authentication. Because this is currently based on a hack, the automatic recognition might mysteriously fail, hence this option to force a prompt. If no password prompt is issued and the backend requires password authentication the connection attempt will fail. __-x, --expanded__ Turns on extended row format mode. This is equivalent to the command __x__. __-X, --no-psqlrc__ Do not read the start-up file ''~/.psqlrc''. __-?, --help__ Shows help about __psql__ command line arguments. !!ADVANCED FEATURES __VARIABLES__ __psql__ provides variable substitution features similar to common Unix command shells. This feature is new and not very sophisticated, yet, but there are plans to expand it in the future. Variables are simply name/value pairs, where the value can be any string of any length. To set variables, use the __psql__ meta-command __set__: testdb=set foo bar __sets the variable ``foo'' to the value ``bar''. To retrieve the content of the variable, precede the name with a colon and use it as the argument of any slash command: testdb=echo :foo __bar __Note:__ The arguments of __set__ are subject to the same substitution rules as with other commands. Thus you can construct interesting references such as set :foo 'something' and get ``soft links'' or ``variable variables'' of Perl or PHP fame, respectively. Unfortunately (or fortunately?), there is no way to do anything useful with these constructs. On the other hand, set bar :foo is a perfectly valid way to copy a variable. If you call __set__ without a second argument, the variable is simply set, but has no value. To unset (or delete) a variable, use the command __unset__. __psql__'s internal variable names can consist of letters, numbers, and underscores in any order and any number of them. A number of regular variables are treated specially by __psql__. They indicate certain option settings that can be changed at runtime by altering the value of the variable or represent some state of the application. Although you can use these variables for any other purpose, this is not recommended, as the program behavior might grow really strange really quickly. By convention, all specially treated variables consist of all upper-case letters (and possibly numbers and underscores). To ensure maximum compatibility in the future, avoid such variables. A list of all specially treated variables follows. __DBNAME__ The name of the database you are currently connected to. This is set every time you connect to a database (including program start-up), but can be unset. __ECHO__ If set to ``all'', all lines entered or from a script are written to the standard output before they are parsed or executed. To specify this on program start-up, use the switch __-a__. If set to ``queries'', __psql__ merely prints all queries as they are sent to the backend. The option for this is __-e__. __ECHO_HIDDEN__ When this variable is set and a backslash command queries the database, the query is first shown. This way you can study the PostgreSQL internals and provide similar functionality in your own programs. If you set the variable to the value ``noexec'', the queries are just shown but are not actually sent to the backend and executed. __ENCODING__ The current client multibyte encoding. If you are not set up to use multibyte characters, this variable will always contain ``SQL_ASCII''. __HISTCONTROL__ If this variable is set to ignorespace, lines which begin with a space are not entered into the history list. If set to a value of ignoredups, lines matching the previous history line are not entered. A value of ignoreboth combines the two options. If unset, or if set to any other value than those above, all lines read in interactive mode are saved on the history list. __Note:__ This feature was shamelessly plagiarized from __bash__. __HISTSIZE__ The number of commands to store in the command history. The default value is 500. __Note:__ This feature was shamelessly plagiarized from __bash__. __HOST__ The database server host you are currently connected to. This is set every time you connect to a database (including program start-up), but can be unset. __IGNOREEOF__ If unset, sending an EOF character (usually Control-D) to an interactive session of __psql__ will terminate the application. If set to a numeric value, that many EOF characters are ignored before the application terminates. If the variable is set but has no numeric value, the default is 10. __Note:__ This feature was shamelessly plagiarized from __bash__. __LASTOID__ The value of the last affected oid, as returned from an __INSERT__ or __lo_insert__ command. This variable is only guaranteed to be valid until after the result of the next SQL command has been displayed. __LO_TRANSACTION__ If you use the PostgreSQL large object interface to specially store data that does not fit into one tuple, all the operations must be contained in a transaction block. (See the documentation of the large object interface for more information.) Since __psql__ has no way to tell if you already have a transaction in progress when you call one of its internal commands (__lo_export__, __lo_import__, __lo_unlink__) it must take some arbitrary action. This action could either be to roll back any transaction that might already be in progress, or to commit any such transaction, or to do nothing at all. In the last case you must provide your own __BEGIN TRANSACTION__/__COMMIT__ block or the results will be unpredictable (usually resulting in the desired action's not being performed in any case). To choose what you want to do you set this variable to one of ``rollback'', ``commit'', or ``nothing''. The default is to roll back the transaction. If you just want to load one or a few objects this is fine. However, if you intend to transfer many large objects, it might be advisable to provide one explicit transaction block around all commands. __ON_ERROR_STOP__ By default, if non-interactive scripts encounter an error, such as a malformed SQL query or internal meta-command, processing continues. This has been the traditional behavior of __psql__ but it is sometimes not desirable. If this variable is set, script processing will immediately terminate. If the script was called from another script it will terminate in the same fashion. If the outermost script was not called from an interactive __psql__ session but rather using the __-f__ option, __psql__ will return error code 3, to distinguish this case from fatal error conditions (error code 1). __PORT__ The database server port to which you are currently connected. This is set every time you connect to a database (including program start-up), but can be unset. __PROMPT1, PROMPT2, PROMPT3__ These specify what the prompt __psql__ issues is supposed to look like. See ``Prompting [[psql(1)]'' below. __QUIET__ This variable is equivalent to the command line option __-q__. It is probably not too useful in interactive mode. __SINGLELINE__ This variable is set by the command line option __-S__. You can unset or reset it at run time. __SINGLESTEP__ This variable is equivalent to the command line option __-s__. __USER__ The database user you are currently connected as. This is set every time you connect to a database (including program start-up), but can be unset. __SQL INTERPOLATION__ An additional useful feature of __psql__ variables is that you can substitute (``interpolate'') them into regular SQL statements. The syntax for this is again to prepend the variable name with a colon (:). testdb=set foo 'my_table' __testdb=__SELECT * FROM :foo; __would then query the table my_table. The value of the variable is copied literally, so it can even contain unbalanced quotes or backslash commands. You must make sure that it makes sense where you put it. Variable interpolation will not be performed into quoted SQL entities. A popular application of this facility is to refer to the last inserted OID in subsequent statements to build a foreign key scenario. Another possible use of this mechanism is to copy the contents of a file into a field. First load the file into a variable and then proceed as above. testdb=set content ''' `cat my_file.txt` ''' __testdb=__INSERT INTO my_table VALUES (:content); __One possible problem with this approach is that ''my_file.txt'' might contain single quotes. These need to be escaped so that they don't cause a syntax error when the third line is processed. This could be done with the program __sed__: testdb=set content ''' `sed -e Observe the correct number of backslashes (6)! You can resolve it this way: After __psql__ has parsed this line, it passes sed -e __sed'' with the arguments -e and s/'/\'/g. When __sed__ parses this it will replace the two backslashes with a single one and then do the substitution. Perhaps at one point you thought it was great that all Unix commands use the same escape character. And this is ignoring the fact that you might have to escape all backslashes as well because SQL text constants are also subject to certain interpretations. In that case you might be better off preparing the file externally. Since colons may legally appear in queries, the following rule applies: If the variable is not set, the character sequence ``colon+name'' is not changed. In any case you can escape a colon with a backslash to protect it from interpretation. (The colon syntax for variables is standard SQL for embedded query languages, such as __ecpg__. The colon syntax for array slices and type casts are PostgreSQL extensions, hence the conflict.) __PROMPTING__ The prompts __psql__ issues can be customized to your preference. The three variables __PROMPT1__, __PROMPT2__, and __PROMPT3__ contain strings and special escape sequences that describe the appearance of the prompt. Prompt 1 is the normal prompt that is issued when __psql__ requests a new query. Prompt 2 is issued when more input is expected during query input because the query was not terminated with a semicolon or a quote was not closed. Prompt 3 is issued when you run an SQL __COPY__ command and you are expected to type in the tuples on the terminal. The value of the respective prompt variable is printed literally, except where a percent sign (``%'') is encountered. Depending on the next character, certain other text is substituted instead. Defined substitutions are: __%M__ The full hostname (with domain name) of the database server, or [[local] if the connection is over a Unix domain socket, or [[local:''/dir/name''], if the Unix domain socket is not at the compiled in default location. __%m__ The hostname of the database server, truncated after the first dot, or [[local] if the connection is over a Unix domain socket. __%__ The port number at which the database server is listening. __%n__ The username you are connected as (not your local system user name). __%/__ The name of the current database. __%~__ Like %/, but the output is ``~'' (tilde) if the database is your default database. __%#__ If the current user is a database superuser, then a ``#'', otherwise a `` __%R__ In prompt 1 normally ``='', but ``^'' if in single-line mode, and ``!'' if the session is disconnected from the database (which can happen if __connect__ fails). In prompt 2 the sequence is replaced by ``-'', ``*'', a single quote, or a double quote, depending on whether __psql__ expects more input because the query wasn't terminated yet, because you are inside a /* ... */ comment, or because you are inside a quote. In prompt 3 the sequence doesn't resolve to anything. __%__''digits'' If ''digits'' starts with 0x the rest of the characters are interpreted as a hexadecimal digit and the character with the corresponding code is substituted. If the first digit is 0 the characters are interpreted as on octal number and the corresponding character is substituted. Otherwise a decimal number is assumed. __%:__''name''__:__ The value of the __psql__, variable ''name''. See the section ``Variables [[psql(1)]'' for details. __%`__''command''__`__ The output of ''command'', similar to ordinary ``back-tick'' substitution. To insert a percent sign into your prompt, write %%. The default prompts are equivalent to '%/%R%# ' for prompts 1 and 2, and ' __Note:__ This feature was shamelessly plagiarized from __tcsh__. __MISCELLANEOUS__ __psql__ returns 0 to the shell if it finished normally, 1 if a fatal error of its own (out of memory, file not found) occurs, 2 if the connection to the backend went bad and the session is not interactive, and 3 if an error occurred in a script and the variable __ON_ERROR_STOP__ was set. Before starting up, __psql__ attempts to read and execute commands from the file ''$HOME/.psqlrc''. It could be used to set up the client or the server to taste (using the __set__ and __SET__ commands). __GNU READLINE__ __psql__ supports the readline and history libraries for convenient line editing and retrieval. The command history is stored in a file named ''.psql_history'' in your home directory and is reloaded when __psql__ starts up. Tab-completion is also supported, although the completion logic makes no claim to be an SQL parser. When available, __psql__ is automatically built to use these features. If for some reason you do not like the tab completion, you can turn if off by putting this in a file named ''.inputrc'' in your home directory: $if psql set disable-completion on $endif (This is not a __psql__ but a __readline__ feature. Read its documentation for further details.) If you have the readline library installed but __psql__ does not seem to use it, you must make sure that PostgreSQL's top-level ''configure'' script finds it. ''configure'' needs to find both the library ''libreadline.a'' (or a shared library equivalent) __and__ the header files ''readline.h'' and ''history.h'' (or ''readline/readline.h'' and ''readline/history.h'') in appropriate directories. If you have the library and header files installed in an obscure place you must tell ''configure'' about them, for example: $ ./configure --with-includes=/opt/gnu/include --with-libs=/opt/gnu/lib ... Then you have to recompile __psql__ (not necessarily the entire code tree). The GNU readline library can be obtained from the GNU project's FTP server at ftp://ftp.gnu.org !!EXAMPLES __Note:__ This section only shows a few examples specific to __psql__. If you want to learn SQL or get familiar with PostgreSQL, you might wish to read the Tutorial that is included in the distribution. The first example shows how to spread a query over several lines of input. Notice the changing prompt: testdb=CREATE TABLE my_table ( __testdb(__ first integer not null default 0, __testdb(__ second text __testdb-__); __CREATE Now look at the table definition again: testdb=d my_table __ Table __At this point you decide to change the prompt to something more interesting: testdb=set PROMPT1 '%n@%m %~%R%# ' __peter@localhost testdb= __Let's assume you have filled the table with data and want to take a look at it: peter@localhost testdb= You can make this table look differently by using the __pset__ command: peter@localhost testdb=pset border 2 __Border style is 2. peter@localhost testdb=__SELECT * FROM my_table; __+-------+--------+ | first | second | +-------+--------+ | 1 | one | | 2 | two | | 3 | three | | 4 | four | +-------+--------+ (4 rows) peter@localhost testdb=__pset border 0 __Border style is 0. peter@localhost testdb=__SELECT * FROM my_table; __first second ----- ------ 1 one 2 two 3 three 4 four (4 rows) peter@localhost testdb=__pset border 1 __Border style is 1. peter@localhost testdb=__pset format unaligned __Output format is unaligned. peter@localhost testdb=__pset fieldsep __Field separator is __pset tuples_only __Showing only tuples. peter@localhost testdb=__SELECT second, first FROM my_table; __one,1 two,2 three,3 four,4 Alternatively, use the short commands: peter@localhost testdb=a t x __Output format is aligned. Tuples only is off. Expanded display is on. peter@localhost testdb=__SELECT * FROM my_table; __-[[ RECORD 1 ]- first | 1 second | one -[[ RECORD 2 ]- first | 2 second | two -[[ RECORD 3 ]- first | 3 second | three -[[ RECORD 4 ]- first | 4 second | four !!APPENDIX __BUGS AND ISSUES__ In some earlier life __psql__ allowed the first argument to start directly after the (single-letter) command. For compatibility this is still supported to some extent but I am not going to explain the details here as this use is discouraged. But if you get strange messages, keep this in mind. For example testdb=foo __Field separator is __which is perhaps not what one would expect. __psql__ only works smoothly with servers of the same version. That does not mean other combinations will fail outright, but subtle and not-so-subtle problems might come up. Pressing Control-C during a ``copy in'' (data sent to the server) doesn't show the most ideal of behaviors. If you get a message such as ``COPY state must be terminated first'', simply reset the connection by entering c - -. ----
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