postgresql/doc/libpgtcl.doc

pgtcl is a tcl package for front-end programs to interface with Postgres95
backends.    PgTcl does not use the libpq library but communicates to
the backend directly via the frontend-backend protocol.  Thus, it is
more efficient than previous postgres->tcl bindings which are layered
on top of libpq.  In addition, pgtcl can handle multiple backend
connections from a single frontend application.

If you have any questions or bug reports, please send them to
Jolly Chen at jolly@cs.berkeley.edu.

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The pgtcl package provides the following commands. 

	pg_connect 	- opens a connection to the backend server
	pg_disconnect   - closes a connection
	pg_exec 	- send a query to the backend
	pg_result 	- manipulate the results of a query

	pg_lo_creat	- create a large object
	pg_lo_open	- open a large object
	pg_lo_close	- close a large object
	pg_lo_read	- read a large object
	pg_lo_write	- write a large object
	pg_lo_lseek	- seek to a position on a large object
	pg_lo_tell	- return the current seek position of a large object
	pg_lo_unlink	- delete a large object
	pg_lo_import	- import a Unix file into a large object
	pg_lo_export	- export a large object into a Unix file

1)  pg_connect:   opens a connection to the backend

   syntax:
        pg_connect dbName [-host hostName] [-port portNumber] [-tty pqtty] [-options optionalBackendArgs]]

   the return result is either an error message or a handle for a database
   connection.  Handles start with the prefix "pgp"


2)  pg_disconnect:	closes a connection

   syntax:
        pg_disconnect connection

   The argument passed in must be a connection pointer.

3)  pg_exec:		send a query string to the backend 

   syntax:
	pg_exec connection query

   the return result is either an error message or a handle for a query
   result.  Handles start with the prefix "pgp"

4)  pg_result:		get information about a query result

   syntax:
        pg_result result ?option? 
	       
    the options are:
         -status  
	      the status of the result
	 -oid
	      if the last query was an insert, returns the oid of the 
	      inserted tuple
	 -conn
	      the connection that produced the result
	 -assign arrayName
	      assign the results to an array
	 -numTuples
	      the number of tuples in the query
	 -attributes
	      returns a list of the name/type pairs of the tuple attributes
	 -getTuple tupleNumber
	      returns the values of the tuple in a list
	 -clear 
	      clear the result buffer. Do not reuse after this

----------------------------------------------------------------------------
The pg_lo* routines are interfaces to the Inversion large objects in postgres.
The functions are designed to mimic the analogous file system functions in
the standard Unix file system interface.

The pg_lo* routines should typically be used within a BEGIN/END transaction
block becaus the file descriptor returned by pg_lo_open is only valid for
the current transaction.  pg_lo_import and pg_lo_export MUST be used
in a BEGIN/END transaction block.

* pg_lo_creat:		create a large object

 syntax:
	g_lo_creat conn mode

mode can be any OR'ing together of INV_READ, INV_WRITE, and INV_ARCHIVE. 
The OR delimiter character is "|".
	e.g. [pg_lo_creat $conn "INV_READ|INV_WRITE"]

returns the oid of the large object created.

* pg_lo_open:		open a large object

 syntax:
	 pg_lo_open conn objOid mode 

 where mode can be either "r", "w", or "rw"

 returns a file descriptor for use in later pg_lo* routines

* pg_lo_close:		close a large object

 syntax:
	 pg_lo_close conn fd 

* pg_lo_read:		read a large object

 syntax:
	pg_lo_read conn fd bufVar len

reads at most len bytes from a large object into a variable named bufVar.
Note that the third argument should be a variable name.

* pg_lo_write:		write a large object

 syntax:
	pg_lo_write conn fd buf len

write at most len bytes to a large object.  
The third argument should be the actual string to write, not a variable name.

* pg_lo_lseek:		seek to a position on a large object

 syntax:
	pg_lo_lseek conn fd offset whence

whence can be "SEEK_CUR", "SEEK_END", or "SEEK_SET"

* pg_lo_tell:		return the current seek position of a large object

 syntax:
	pg_lo_tell conn fd

* pg_lo_unlink:		delete a large object 

 syntax:
	pg_lo_unlink conn lobjId

* pg_lo_import:		import a Unix file into a large object

 syntax:
	pg_lo_import conn filename

  pg_lo_import must be called within a BEGIN/END transaction block

* pg_lo_export:		export a large object into a Unix file
 
 syntax:
	pg_lo_export conn lobjId filename

  pg_lo_export must be called within a BEGIN/END transaction block

------------------------------------------------------------------
Here's a small example of how to use the routines:

# getDBs :
#   get the names of all the databases at a given host and port number
#   with the defaults being the localhost and port 5432
#   return them in alphabetical order
proc getDBs { {host "localhost"} {port "5432"} } {
    # datnames is the list to be result
    set conn [pg_connect template1 -host $host -port $port]
    set res [pg_exec $conn "SELECT datname FROM pg_database ORDER BY datname"]
    set ntups [pg_result $res -numTuples]
    for {set i 0} {$i < $ntups} {incr i} {
	lappend datnames [pg_result $res -getTuple $i]
    }
    pg_disconnect $conn
    return $datnames
}