psql - Unix, Linux Command

NAME

SYNOPSIS

psql [ option... ] [ dbname
[ username ] ]

DESCRIPTION

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.

OPTIONS

EXIT STATUS

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 server went bad and the session was not interactive, and 3 if an error occurred in a script and the variable ON_ERROR_STOP was set.

USAGE

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 host name 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 already given). Not all these options are required; there are useful defaults. If you omit the host name, psql will connect via a Unix-domain socket to a server on the local host, or via TCP/IP to localhost on machines that don’t have Unix-domain sockets. The default port number is determined at compile time. 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 user name, as is the default database name. Note that you can’t just connect to any database under any user name. Your database administrator should have informed you about your access rights.

When the defaults aren’t quite right, you can save yourself some typing by setting the environment variables PGDATABASE, PGHOST, PGPORT and/or PGUSER to appropriate values. (For additional environment variables, see the documentation.) It is also convenient to have a ~/.pgpass file to avoid regularly having to type in passwords. See the documentation for more information.

If the connection could not be made for any reason (e.g., insufficient privileges, server is not running on the targeted host, etc.), psql will return an error and terminate.

ENTERING SQL COMMANDS

In normal operation, psql provides a prompt with the name of the database to which psql is currently connected, followed by the string =>. For example,

$ psql testdb
Welcome to psql 8.1.22, the PostgreSQL interactive terminal.

Type:  \copyright for distribution terms
       \h for help with SQL commands
       \? for help with psql commands
       \g or terminate with semicolon to execute query
       \q to quit

testdb=>

At the prompt, the user may type in SQL commands. Ordinarily, input lines are sent to the server when a command-terminating semicolon is reached. An end of line does not terminate a command. Thus commands can be spread over several lines for clarity. If the command was sent and executed without error, the results of the command are displayed on the screen.

Whenever a command is executed, psql also polls for asynchronous notification events generated by LISTEN [listen(7)] and NOTIFY [notify(7)].

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 help make psql more useful 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 may 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 (octal), and \xdigits (hexadecimal).

If an unquoted argument begins with a colon (:), it is taken as a psql variable and the value of the variable is used as the argument instead.

Arguments that are enclosed in backquotes (‘) are taken as a command line that is passed to the shell. The output of the command (with any trailing newline removed) is taken as the argument value. The above escape sequences also apply in backquotes.

Some commands take an SQL identifier (such as a table name) as argument. These arguments follow the syntax rules of SQL: Unquoted letters are forced to lowercase, while double quotes (") protect letters from case conversion and allow incorporation of whitespace into the identifier. Within double quotes, paired double quotes reduce to a single double quote in the resulting name. For example, FOO"BAR"BAZ is interpreted as fooBARbaz, and "A weird"" name" becomes A weird" name.

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 commands, 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:

=> \dd version
                     Object descriptions
   Schema   |  Name   |  Object  |        Description
------------+---------+----------+---------------------------
 pg_catalog | version | function | PostgreSQL version string
(1 row)

=> \echo ‘date‘
Tue Oct 26 21:40:57 CEST 1999

foo=> \lo_import ’/home/peter/pictures/photo.xcf’ ’a picture of me’
lo_import 152801

The various \d commands accept a pattern parameter to specify the object name(s) to be displayed. * means ‘‘any sequence of characters’’ and ? means ‘‘any single character’’. (This notation is comparable to Unix shell file name patterns.) Advanced users can also use regular-expression notations such as character classes, for example [0-9] to match ‘‘any digit’’. To make any of these pattern-matching characters be interpreted literally, surround it with double quotes.

A pattern that contains an (unquoted) dot is interpreted as a schema name pattern followed by an object name pattern. For example, \dt foo*.bar* displays all tables in schemas whose name starts with foo and whose table name starts with bar. If no dot appears, then the pattern matches only objects that are visible in the current schema search path.

Whenever the pattern parameter is omitted completely, the \d commands display all objects that are visible in the current schema search path. To see all objects in the database, use the pattern *.*.

ADVANCED FEATURES

VARIABLES

psql provides variable substitution features similar to common Unix command shells. 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

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 set, with an empty string as 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 these variables are treated specially by psql. They indicate certain option settings that can be changed at run time 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 using such variable names for your own purposes. A list of all specially treated variables follows.

\set HISTFILE ~/.psql_history- :DBNAME

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;

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 table column. First load the file into a variable and then proceed as above.

testdb=> \set content ’#146;’ ‘cat my_file.txt‘ ’#146;’
testdb=> INSERT INTO my_table VALUES (:content);

testdb=> \set content ’#146;’ ‘sed -e "s/’/\\\\\#146;/g" < my_file.txt‘ ’#146;’

Since colons may legally appear in SQL commands, the following rule applies: the character sequence ‘‘:name’’ is not changed unless ‘‘name’’ is the name of a variable that is currently set. In any case you can escape a colon with a backslash to protect it from substitution. (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 command. Prompt 2 is issued when more input is expected during command input because the command 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 row values on the terminal.

The value of the selected 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:

testdb=> \set PROMPT1 ’%[%033[1;33;40m%]%n@%/%R%[%033[0m%#%] ’

COMMAND-LINE EDITING

psql supports the Readline library for convenient line editing and retrieval. The command history is automatically saved when psql exits and is reloaded when psql starts up. Tab-completion is also supported, although the completion logic makes no claim to be an SQL parser. If for some reason you do not like the tab completion, you can turn it off by putting this in a file named .inputrc in your home directory:

$if psql
set disable-completion on
$endif

ENVIRONMENT

FILES

NOTES

testdb=> \foo
Field separator is "oo".

NOTES FOR WINDOWS USERS

psql is built as a ‘‘console application’’. Since the Windows console windows use a different encoding than the rest of the system, you must take special care when using 8-bit characters within psql. If psql detects a problematic console code page, it will warn you at startup. To change the console code page, two things are necessary:

EXAMPLES

The first example shows how to spread a command 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 TABLE

testdb=> \d my_table
             Table "my_table"
 Attribute |  Type   |      Modifier
-----------+---------+--------------------
 first     | integer | not null default 0
 second    | text    |

testdb=> \set PROMPT1 ’%n@%m %~%R%# ’
peter@localhost testdb=>

peter@localhost testdb=> SELECT * FROM my_table;
 first | second
-------+--------
     1 | one
     2 | two
     3 | three
     4 | four
(4 rows)

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 ",".
peter@localhost testdb=> \pset tuples_only
Showing only tuples.
peter@localhost testdb=> SELECT second, first FROM my_table;
one,1
two,2
three,3
four,4

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

SEE ALSO