Hello pwagyi

I am not really sure, if the lexical names that you use e.g. read_data, data_to_modify, out_fh->write are your functions or they come from the use of a module. Since we do not have this information I will assume that you are using your functions etc.

What are you trying to do exactly? I mean are you trying to simply read and write to a file or there is also something else happening? I see from your code that you read and write to the file twice why? Also why are you using last instead of next? I would suggest to use defined to avoid having problems with lines after chomp. Also why not skip the blank lines in your file that could also boost your reading process (in case there are empty lines).

Sample of code:

#!/usr/bin/perl
use strict;
use warnings;
use feature 'say';

my $file = 'file.txt';

open(my $fh, "<", $file)
    or die "Can't open ".$file." error: $!";

while( defined( my $line = <$fh> ) ) {
    chomp $line;
    next if $line =~ /^\s*$/; # skip empty lines
    next if (index($line, 'second') != -1);
    say $line;
}

close $fh
    or warn "Can't close ".$file." error: $!";

__DATA__

This is the first line in the file.

This is the second line in the file.

This is the third line in the file.
This is the forth line in the file.

__OUTPUT__

$ perl test.pl
This is the first line in the file.
This is the third line in the file.
This is the forth line in the file.
[download]

If you want to read and write to a file have you tried Tie::File? Sample of code using IO::All module which includes the methods of Tie::File.

#!/usr/bin/perl
use strict;
use IO::All;
use warnings;
use Data::Dumper;
use feature 'say';

my $io = io 'file.txt';

# Miscellaneous:
my @lines = $io->chomp->slurp;

print Dumper \@lines;

# Tie::File support:
$io->[2] = 'This is the changed line in the file.';             # Chan
+ge a line
say $io->[@$io / 2];                      # Print middle line

print Dumper \@lines;

__DATA__

This is the first line in the file.
This is the second line in the file.
This is the third line in the file.
This is the forth line in the file.

__OUTPUT__

$ perl test.pl
$VAR1 = [
          'This is the first line in the file.',
          'This is the second line in the file.',
          'This is the third line in the file.',
          'This is the forth line in the file.'
        ];
This is the changed line in the file.
$VAR1 = [
          'This is the first line in the file.',
          'This is the second line in the file.',
          'This is the changed line in the file.',
          'This is the forth line in the file.'
        ];
[download]

Update: I noticed that maybe you are working with binary files. So maybe my sample of code is not applicable in your case. Let's assume for the moment that you are working with binaries. Again my question why since you are altering a file why you need to copy and paste it after again, since the original file is updated to your new version? If for any reason you want to create a copy of the altered file and you think that cp is faster than copying the whole file through Perl, why you do not apply it through the command line? You can use Capture::Tiny for this job.

Sample of code:

#!/usr/bin/perl
use strict;
use warnings;
use Capture::Tiny 'capture';

my $original = 'file.txt';
my $copy = 'fileTest.txt';

my $cmd = qq{cp -v $original $copy};

# capture from external command
my ($stdout, $stderr, $exitCode) = capture {
    system( $cmd );
};

print 'StdOut: ' . $stdout if $exitCode == 0;
print 'Error: ' . $stderr unless $exitCode == 0;

__END__

$ perl test.pl
StdOut: 'file.txt' -> 'fileTest.txt'
[download]

Hope this helps, BR.

If you want to read and write to a file have you tried Tie::File? Sample of code using IO::All module which includes the methods of Tie::File.

Hi, have you tried using Tie::File to edit a >2GB file ? Tie::File is slow, to write a 1mb file 137.506 seconds, versus 0.197 seconds without it

That would make a 2GB file take 3+days Tie::File is super slow, to print the 20/40 millionth lines in a 3GB file takes more than 30-40 minutes , versus 12 seconds without it

 

shouter shouts

'Modify' as in adding/removing bytes. Output file might be bigger or smaller.