See the current Perl documentation for lib:SelectSaver.
Here is our local, out-dated (pre-5.6) version:

SelectSaver - save and restore selected file handle

use SelectSaver;
{
my $saver = new SelectSaver(FILEHANDLE);
# FILEHANDLE is selected
}
# previous handle is selected
{
my $saver = new SelectSaver;
# new handle may

A SelectSaver object contains a reference to the file handle that was selected when it
was created. If its new method gets an extra parameter, then that parameter is selected; otherwise,
the selected file handle remains unchanged.
When a SelectSaver is destroyed, it re-selects the file handle that was selected when it was
created.