I have a log file with some numeric data like

abc.log
12
15
17

[download]

I want to update the value present at offset 3 i.e 15 in this case with a given value like 20. I had done something like this

write_log("12345");

sub write_log {
    my ($message) = @_;

    my $new_data = '';
    my $header_fields_value = 0;
    my $length = length $message;
    open (MYFILE, '>>', 'abc.log');
    $header_fields_value = read_line(3);
    $new_data = $header_fields_value+$length+2;
    $header_fields_value =~ s/$header_fields_value/$new_data/g;
    seek(MYFILE,3,0);
    print MYFILE $header_fields_value;

    close (MYFILE);
}

sub read_line {
    my ($offset) = @_;
    open (MYFILE1, '<', $filename); 
    seek(MYFILE1,$offset,0);
    my $line = <MYFILE1>;
    close (MYFILE1);
    return($line);
}

[download]

here it is reading the value stored at offset 3 using read_line function. But modified value is being appended at the end of the file. I need it to replace the line present at offset 3.

Please help me in understanding what am i doing wrong or if it could be done in some easier way.

In reply to Replace a text in file at given offset with other text by tarun28jain

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