Suppose we are replacing a record with another of exactly the same length
Then we need not rewrite the entire file
For example:
sub uppercase_username {
my ($fh, $username) = @_;
seek $fh, 0, SEEK_SET;
while (<$fh>) {
my ($u, $rest) = split /:/, $_, 2;
next unless $u eq $username;
seek $fh, -length($_), SEEK_CUR;
print $fh uc($u);
return;
}
}
We search the file as usual
When we find the record we want, we back up and overwrite it in place