$ psql "service=myservice sslmode=require"
$ psql postgresql://dbmaster:5433/mydb?sslmode=require

$ psql testdb
psql (9.2.24)
Type "help" for help.
testdb=>

Where the command omits database name, user, host, or port, the new connection can reuse values from the previous connection. By default, values from the previous connection are reused except when processing a conninfo string. Passing a first argument of -reuse-previous=on or -reuse-previous=off overrides that default. When the command neither specifies nor reuses a particular parameter, the libpq default is used. Specifying any of dbname, username, host or port as - is equivalent to omitting that parameter.

If the new connection is successfully made, the previous connection is closed. If the connection attempt failed (wrong user name, access denied, etc.), the previous connection will only be kept 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.

Examples:

=> \c mydb myuser host.dom 6432
=> \c service=foo
=> \c "host=localhost port=5432 dbname=mydb connect_timeout=10 sslmode=disable"
=> \c postgresql://tom@localhost/mydb?application_name=myapp

The syntax of the command is similar to that of the SQLCOPY(7) command. 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.

\copy ... from stdin | to stdout reads/writes based on the command input and output respectively. All rows are read from the same source that issued the command, continuing until \. is read or the stream reaches EOF. Output is sent to the same place as command output. To read/write from psql's standard input or output, use pstdin or pstdout. This option is useful for populating tables in-line within a SQL script file.

For some types of relation, \d shows additional information for each column: column values for sequences, indexed expression for indexes and foreign data wrapper options for foreign tables.

The command form \d+ is identical, except that more information is displayed: any comments associated with the columns of the table are shown, as is the presence of OIDs in the table, the view definition if the relation is a view.

By default, only user-created objects are shown; supply a pattern or the S modifier to include system objects.

\dd displays descriptions for objects matching the pattern, or of visible objects of the appropriate type if no argument is given. But in either case, only objects that have a description are listed. By default, only user-created objects are shown; supply a pattern or the S modifier to include system objects.

Descriptions for objects can be created with the COMMENT(7)SQL command.

The ALTER DEFAULT PRIVILEGES (ALTER_DEFAULT_PRIVILEGES(7)) command is used to set default access privileges. The meaning of the privilege display is explained under GRANT(7).

The GRANT(7) and REVOKE(7) commands are used to set access privileges. The meaning of the privilege display is explained under GRANT(7).

The ALTER ROLE (ALTER_ROLE(7)) and ALTER DATABASE (ALTER_DATABASE(7)) commands are used to define per-role and per-database configuration settings.

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 that if the query ends with (or contains) a semicolon, it is immediately executed. Otherwise it will merely wait in the query buffer; type semicolon or \g to send it, or \r to cancel.

If a line number is specified, psql will position the cursor on the specified line of the file or query buffer. Note that if a single all-digits argument is given, psql assumes it is a line number, not a file name.

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

If the first argument is an unquoted -n the trailing newline is not written.

The target function can be specified by name alone, or by name and arguments, for example foo(integer, text). The argument types must be given if there is more than one function of the same name.

If no function is specified, a blank CREATE FUNCTION template is presented for editing.

If a line number is specified, psql will position the cursor on the specified line of the function body. (Note that the function body typically does not begin on the first line of the file.)

If filename is - (hyphen), then standard input is read until an EOF indication or \q meta-command. This can be used to intersperse interactive input with input from files. Note that Readline behavior will be used only if it is active at the outermost level.

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 can be used to access the newly-created large object in the future. For the sake of readability, it is recommended to always associate a human-readable comment with every object. Both OIDs and comments can be viewed 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.

“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.

By default, \prompt uses the terminal for input and output. However, if the -f command line switch was used, \prompt uses standard input and standard output.

Adjustable printing options are:

border

columns

expanded (or x)

fieldsep

fieldsep_zero

footer

format

linestyle

null

numericlocale

pager

recordsep

recordsep_zero

tableattr (or T)

title

tuples_only (or t)

Illustrations of how these different formats look can be seen in the EXAMPLES section.

\set without any arguments displays the names and values of all currently-set psql variables.

Valid variable names can contain letters, digits, and underscores. See the section Variables below for details. Variable names are case-sensitive.

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.

The target function can be specified by name alone, or by name and arguments, for example foo(integer, text). The argument types must be given if there is more than one function of the same name.

If + is appended to the command name, then the output lines are numbered, with the first line of the function body being line 1.

This is an alias for \dp (“display privileges”).

The various \d commands accept a pattern parameter to specify the object name(s) to be displayed. In the simplest case, a pattern is just the exact name of the object. The characters within a pattern are normally folded to lower case, just as in SQL names; for example, \dt FOO will display the table named foo. As in SQL names, placing double quotes around a pattern stops folding to lower case. Should you need to include an actual double quote character in a pattern, write it as a pair of double quotes within a double-quote sequence; again this is in accord with the rules for SQL quoted identifiers. For example, \dt "FOO""BAR" will display the table named FOO"BAR (not foo"bar). Unlike the normal rules for SQL names, you can put double quotes around just part of a pattern, for instance \dt FOO"FOO"BAR will display the table named fooFOObar.

Whenever the pattern parameter is omitted completely, the \d commands display all objects that are visible in the current schema search path — this is equivalent to using * as the pattern. (An object is said to be visible if its containing schema is in the search path and no object of the same kind and name appears earlier in the search path. This is equivalent to the statement that the object can be referenced by name without explicit schema qualification.) To see all objects in the database regardless of visibility, use *.* as the pattern.

Within a pattern, * matches any sequence of characters (including no characters) and ? matches any single character. (This notation is comparable to Unix shell file name patterns.) For example, \dt int* displays tables whose names begin with int. But within double quotes, * and ? lose these special meanings and are just matched literally.

A pattern that contains a dot (.) is interpreted as a schema name pattern followed by an object name pattern. For example, \dt foo*.*bar* displays all tables whose table name includes bar that are in schemas whose schema name starts with foo. When no dot appears, then the pattern matches only objects that are visible in the current schema search path. Again, a dot within double quotes loses its special meaning and is matched literally.

Advanced users can use regular-expression notations such as character classes, for example [0-9] to match any digit. All regular expression special characters work as specified in Section 9.7.3, “POSIX Regular Expressions”, in the documentation, except for . which is taken as a separator as mentioned above, * which is translated to the regular-expression notation .*, ? which is translated to ., and $ which is matched literally. You can emulate these pattern characters at need by writing ? for ., (R+|) for R*, or (R|) for R?. $ is not needed as a regular-expression character since the pattern must match the whole name, unlike the usual interpretation of regular expressions (in other words, $ is automatically appended to your pattern). Write * at the beginning and/or end if you don't wish the pattern to be anchored. Note that within double quotes, all regular expression special characters lose their special meanings and are matched literally. Also, the regular expression special characters are matched literally in operator name patterns (i.e., the argument of \do).

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. The name must consist of letters (including non-Latin letters), digits, and underscores.

To set a variable, use the psql meta-command \set. For example,

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, for example:

testdb=> \echo :foo
bar

This works in both regular SQL commands and meta-commands; there is more detail in SQL Interpolation, below.

If you call \set without a second argument, the variable is set, with an empty string as value. To unset (i.e., delete) a variable, use the command \unset. To show the values of all variables, call \set without any argument.

A number of these variables are treated specially by psql. They represent certain option settings that can be changed at run time by altering the value of the variable, or in some cases represent changeable state of psql. Although you can use these variables for other purposes, this is not recommended, as the program behavior might grow really strange really quickly. By convention, all specially treated variables' names consist of all upper-case ASCII letters (and possibly digits 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.

AUTOCOMMIT

COMP_KEYWORD_CASE

DBNAME

ECHO

ECHO_HIDDEN

ENCODING

FETCH_COUNT

HISTCONTROL

HISTFILE

\set HISTFILE ~/.psql_history- :DBNAME

HISTSIZE

HOST

IGNOREEOF

LASTOID

ON_ERROR_ROLLBACK

ON_ERROR_STOP

PORT

PROMPT1, PROMPT2, PROMPT3

QUIET

SINGLELINE

SINGLESTEP

USER

VERBOSITY

A key feature of psql variables is that you can substitute (“interpolate”) them into regular SQL statements, as well as the arguments of meta-commands. Furthermore, psql provides facilities for ensuring that variable values used as SQL literals and identifiers are properly quoted. The syntax for interpolating a value without any quoting is to prepend the variable name with a colon (:). For example,

testdb=> \set foo 'my_table'
testdb=> SELECT * FROM :foo;

would query the table my_table. Note that this may be unsafe: the value of the variable is copied literally, so it can contain unbalanced quotes, or even backslash commands. You must make sure that it makes sense where you put it.

When a value is to be used as an SQL literal or identifier, it is safest to arrange for it to be quoted. To quote the value of a variable as an SQL literal, write a colon followed by the variable name in single quotes. To quote the value as an SQL identifier, write a colon followed by the variable name in double quotes. These constructs deal correctly with quotes and other special characters embedded within the variable value. The previous example would be more safely written this way:

testdb=> \set foo 'my_table'
testdb=> SELECT * FROM :"foo";

Variable interpolation will not be performed within quoted SQL literals and identifiers. Therefore, a construction such as ':foo' doesn't work to produce a quoted literal from a variable's value (and it would be unsafe if it did work, since it wouldn't correctly handle quotes embedded in the value).

One example 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 interpolate the variable's value as a quoted string:

testdb=> \set content `cat my_file.txt`
testdb=> INSERT INTO my_table VALUES (:'content');

(Note that this still won't work if my_file.txt contains NUL bytes. psql does not support embedded NUL bytes in variable values.)

Since colons can legally appear in SQL commands, an apparent attempt at interpolation (that is, :name, :'name', or :"name") is not replaced unless the named variable 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 syntaxes for array slices and type casts are PostgreSQL extensions, which can sometimes conflict with the standard usage. The colon-quote syntax for escaping a variable's value as an SQL literal or identifier is a psql extension.

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 entry, for example because the command was not terminated with a semicolon or a quote was not closed. Prompt 3 is issued when you are running an SQLCOPY FROM STDIN command and you need to type in a row value 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:

%M

%m

%>

%n

%/

%~

%#

%R

%x

%digits

%:name:

%`command`

%[ ... %]

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

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

(This is not a psql but a Readline feature. Read its documentation for further details.)