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sub modify {
my ($fh, $rec) = @_;
my $pos = tell $fh;
chomp(my $oldrec = <$fh>);
seek $fh, $pos, SEEK_SET;
if (length $oldrec == length $rec) {
# easy case
print $fh $rec;
} elsif (length $rec < length $oldrec) {
my $shortfall = length($oldrec) - length($rec);
my $fill = "\0" x ($shortfall-1);
print $fh $rec, "\n", $fill;
... continued ...
In this case, the new record will fit in the old space
Say we're changing tchrist:A3Jye3/wLzQNs\n to tom:A3Jye3/wLzQNs\n
We actually change it to tom:A3Jye3/wLzQNs\n\0\0\0\n
This is the same length
find will ignore the \0\0\0\n 'gap'
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Copyright © 2003 M. J. Dominus |