in reply to Re^4: substitute on file line by line not working syntax error
in thread Search and Replace line by line not working on Filehandle

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

[download]

Replies are listed 'Best First'.
Re^6: substitute on file line by line not working syntax error
by matze77 (Friar) on Jan 15, 2010 at 11:03 UTC

    OK. Seems i have to use the "Seek thing". This seems to work:

    #!/usr/bin/perl
use strict;
use warnings;

open (IN, "+<C:/oracle/ora81/network/ADMIN/SQLNET.ORA") || die "cant o
+pen $!";

my @file = <IN>;

seek IN,0,0;

foreach my $file (@file){
$file =~ s/^SQLNET\.AUTHENTICATION_SERVICES=\ \(NTS\)$/#\ SQLNET\.AUTH
+ENTICATION_SERVICES=\ \(NTS\)/i;
print IN $file;
}
close IN;

    [download]

    Thanks
    MH
[reply]
[d/l]
      I'm surprised it works - are you sure?
      seek IN,0,0; just sets the position to beginning of file. See seek.
[reply]
[d/l]
        Yes. Honestly i must admit i found this on the web and just changed it to my needs, without understanding it completely, since it worked i didnt bother for the moment ...

[reply]

In Section Seekers of Perl Wisdom