(print "Program Error!" && exit(0)) unless ([case is true]);

##</code><code>##

# open the file - read
# swap the update_info=blah line to update_info=auto
my @lines = map {s/^update_info=(?:\w+)/update_info=auto/; $_ } <FILE>;
# close file

# open the file - write
foreach (@lines) { print TOFILE; }
# close file