how to change the contents in the file in perl? - perl

Question

I am trying to open one file read oneline in it at a time then open the another file and try to search for some part of the line read from the first file in the second file and try to replace all instances with the other part of the line read from the first file.When i am executing it its getting executed and i am able to see the result on the console but the files are not getting modified. What could be the mistake. Can some one please suggest this.
use strict;
use warnings;
use autodie; # die if problem reading or writing a file
my $filename = 'compare.txt';
open(my $fh, '+<', $filename) or die "Could not open file '$filename' $!";
while(<$fh>){
my $readline= "$_";
print("\n");
my #arr=split(',',$readline);
print($arr[0]."\n".$arr[1]);
replace($arr[0],$arr[1]);
}
close $fh;
sub replace
{
my $search=shift(#_);
my $replace=shift(#_);
my $filename2 = 'replace.txt';
open(my $fh1, '+<', $filename2) or die "Could not open file '$filename' $!";
while(<$fh1>)
{
my $readline2= "$_";
$readline2=~s/$search/$replace/g;
print($readline2);
print("\n");
}
close $fh1;
}

Answer 1

As a huge fan of the Path::Tiny module, I would do the above as:
use 5.014;
use warnings;
use Path::Tiny;
my %rep = map { split /,/ } path('compare.txt')->lines({chomp => 1});
path("replace.txt")->edit_lines( sub {
while(my($key,$val) = each(%rep)) {
s/$key/$val/g;
}
});

Answer 2

In your sub, when you are iterating the lines in your file, you should write it back to a file. The regex substitute doesn't automatically write it back to file.
use strict;
use warnings;
use autodie; # die if problem reading or writing a file
use File::Copy;
my $filename = 'compare.txt';
open(my $fh, '+<', $filename) or die "Could not open file '$filename' $!";
while(<$fh>){
my $readline= "$_";
print("\n");
my #arr=split(',',$readline);
print($arr[0]."\n".$arr[1]);
replace($arr[0],$arr[1]);
}
close $fh;
sub replace
{
my $search=shift(#_);
my $replace=shift(#_);
my $filename2 = 'replace.txt';
open(my $fh1, '+<', $filename2) or die "Could not open file '$filename' $!";
#open file to write to
open $newfile, '>', 'replace_tmp.txt';
while(<$fh1>)
{
chomp;
my $readline2= "$_";
$readline2=~s/$search/$replace/g;
print( $newfile, $readline2);
print($newfile, "\n");
}
close($fh1);
close($newfile);
move ('replaced.txt', 'replace.txt');
}
This is simple way of doing it. You can use File::Tie to write back to the same file and avoid renaming it, or refer to perldoc