Lightweight Databases

Copy the File

The simplest and most often-cited solution is to copy the file
- Make the changes as you write the copy
- Then replace the original with the copy
For example, deleting billg:

        sub delete_user {
          my ($file, $target_user) = @_;
          open my $rfh, "<", $file or die ...;
          open my $wfh, ">", "$file.tmp" or die ...;
          while (<$rfh>) {
            my ($user) = split /:/;
            print $wfh unless $user eq $target_user;
          }
          close $rfh; close $wfh or die ...;
          rename "$file.tmp", $file or die ...;
        }

Or appending to a log file:

        sub append_log {
          my ($file, @newrecs) = @_;
          open my $rfh, "<", $file or die ...;
          open my $wfh, ">", "$file.tmp" or die ...;
          my @recs = (<$rfh>, @newrecs);
          splice @recs, 0, @recs-$MAXRECS if @recs > $MAXRECS;
          print $wfh @recs;
          close $rfh; close $wfh or die ...;
          rename "$file.tmp", $file or die ...;
        }