Well, as long as you can be sure its the last line,
you can find out where the last line is and use truncate,
and then append the new last line.
I have an example here where I just replace the
whole __DATA__ portion:
#!/usr/bin/perl -w
use strict;
my $new = "new text here!\n";
my $data_pos = tell DATA;
open SELF, "+<$0" or die "open $0: $!\n";
truncate SELF, $data_pos or die "truncate: $!\n";
seek SELF, 0, 2 or die "seek: $!\n"; # append now.
print SELF "$new" or die "print: $!\n"; # just in case
close SELF or die "while closing $0: $!\n";
__DATA__
this is the stuff to replace
Be aware that this has a race condition if two copies
of the script are run at once. The race condition
can be eliminated by adding an flock after open
as long as it can be gaurenteed that the script (before
the __DATA__) will
not be modified while it runs.
update: (more) minor typos fixed,
die check added, (more recently) rephrased to actually explain algorithm. |