in reply to Re: substitute on file line by line not working syntax error
in thread Search and Replace line by line not working on Filehandle

changed this the comma was missing: 
print OUT $_ , "\#\ SQLNET\.AUTHENTICATION_SERVICES=\ (NTS)";

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OK. Now the line prints, i wanted it to overwrite the original line but it prints to the next line maybe i need to "remember" the line number and overwrite it?
result: 
SQLNET.AUTHENTICATION_SERVICES= (NTS)
1# SQLNET.AUTHENTICATION_SERVICES= (NTS)<p>

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Are the parentheses around (NTS) interpreted as "backreference" and printed before as 1 ...?

Thanks
MH

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Re^3: substitute on file line by line not working syntax error
by ikegami (Patriarch) on Jan 15, 2010 at 09:03 UTC
    If you want just the new line, not the old and the new one, don't print the old one ($_).
[reply]
      Ah ok. Thanks. Thats one fault (recycled old code without thinking first). But it prints a line **after** the line that should be changed, i want to **overwrite** the line not "append". Any idea? Something like moving the "Write Pointer" back 1 line and write it there?


      Thanks
      MH
[reply]
        Sure you can, BUT the new record (line) must be exactly the same length as the old one. For example, if you just want to comment out a line by placing a '#' at the front then you cannot overwrite the existing line since that would be one extra character - you would overwrite the first character of the next line in the file.

        Here is a simple example where the new line is the same length as the old:
        use warnings;
use strict;
use Fcntl qw(SEEK_CUR);

# open existing file for read/write
open (my $in, '+<', 'file1.txt') || die "Unable to open file1.txt:$!";

while (<$in>) {

    # Identify the record
    if (/4444/) {
         # Construct the new record
         s/4/#/g;

         # Position the file pointer
         seek ($in, -length($_)-1, SEEK_CUR);
         print $in $_;
    }
}

close $in;

        [download]
        Input file was:
        111111111111111
22222222
33333333333
4444444
5555555555555555
66666666666

        [download]
        file after processing is:
        111111111111111
22222222
33333333333
#######
555555555555555
66666666666

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