adminpack provides a number of support functions which
  pgAdmin and other administration and management tools can
  use to provide additional functionality, such as remote management
  of server log files.
  Use of all these functions is only allowed to the superuser by default but may be
  allowed to other users by using the GRANT command.
 
The functions shown in Table F.1 provide write access to files on the machine hosting the server. (See also the functions in Table 9.94, which provide read-only access.) Only files within the database cluster directory can be accessed, unless the user is a superuser or given one of the pg_read_server_files, or pg_write_server_files roles, as appropriate for the function, but either a relative or absolute path is allowable.
Table F.1. adminpack Functions
| Name | Return Type | Description | 
|---|---|---|
| pg_catalog.pg_file_write(filename text, data text, append boolean) | bigint | Write, or append to, a text file | 
| pg_catalog.pg_file_rename(oldname text, newname text [, archivename text]) | boolean | Rename a file | 
| pg_catalog.pg_file_unlink(filename text) | boolean | Remove a file | 
| pg_catalog.pg_logdir_ls() | setof record | List the log files in the log_directorydirectory | 
  pg_file_write writes the specified data into
  the file named by filename.  If append is
  false, the file must not already exist.  If append is true,
  the file can already exist, and will be appended to if so.
  Returns the number of bytes written.
 
  pg_file_rename renames a file.  If archivename
  is omitted or NULL, it simply renames oldname
  to newname (which must not already exist).
  If archivename is provided, it first
  renames newname to archivename (which must
  not already exist), and then renames oldname
  to newname.  In event of failure of the second rename step,
  it will try to rename archivename back
  to newname before reporting the error.
  Returns true on success, false if the source file(s) are not present or
  not writable; other cases throw errors.
 
  pg_file_unlink removes the specified file.
  Returns true on success, false if the specified file is not present
  or the unlink() call fails; other cases throw errors.
 
  pg_logdir_ls returns the start timestamps and path
  names of all the log files in the log_directory
  directory.  The log_filename parameter must have its
  default setting (postgresql-%Y-%m-%d_%H%M%S.log) to use this
  function.