Saving and restoring standard file descriptors of shell scripts

How can a shell script save and restore its standard file descriptors (stdin, stdout and stderr)?

Angel Tsankov wrote:
[color=blue]
> How can a shell script save and restore its standard file descriptors
> (stdin, stdout and stderr)?[/color]

one common trick is

# move FD 1 to FD 20
exec 20>&1 1>&/some/other/file
....

# move FD 1 back to original
exec 1>&20

this assumes that shell supports multidigit FD number (some older shells do
not) and FD 20 is not used (e.g. it may be inherited and contain SSH agent
connection ...)