PostgreSQL 7.2.1 Documentation
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# Chapter 4. pgtcl - Tcl Binding Library

# 4.1. Introduction

pgtcl is a Tcl package for client programs to interface with PostgreSQL servers. It makes most of the functionality of libpq available to Tcl scripts.

This package was originally written by Jolly Chen.

Table 4-1 gives an overview over the commands available in pgtcl. These commands are described further on subsequent pages.

Table 4-1. `pgtcl` Commands

Command | Description
--- | ---
`pg_connect` | opens a connection to the backend server
`pg_disconnect` | closes a connection
`pg_conndefaults` | get connection options and their defaults
`pg_exec` | send a query to the backend
`pg_result` | manipulate the results of a query
`pg_select` | loop over the result of a SELECT statement
`pg_listen` | establish a callback for NOTIFY messages
`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 in 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

The `pg_lo_*` routines are interfaces to the large object features of PostgreSQL. The functions are designed to mimic the analogous file system functions in the standard Unix file system interface. The `pg_lo_*` routines should be used within a BEGIN/COMMIT transaction block because 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/COMMIT transaction block.

Example 4-1 shows a small example of how to use the routines.

Example 4-1. pgtcl Example Program

    # 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_result $res -clear
        pg_disconnect $conn
        return $datnames
    }

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