Compare two files and write matching data from first file using perl - perl

Question

First file
FirstName:LastName:Location:Country:ID
FirstName1:LastName1:Location1:Country1:ID1
FirstName2:LastName2:Location2:Country2:ID2
FirstName3:LastName3:Location3:Country3:ID3
FirstName4:LastName4:Location4:Country4:ID4
Second file
FirstName:LastName:Location:Country:Old_ID
FirstName2:LastName2:Location2:Country2:Old_ID2
FirstName4:LastName4:Location4:Country4:Old_ID4
Have to compare first and second file and print matching rows with data from first file which is have new ID's.
Below script fetches me Old_ID's from second file and not the new ones from first file
use warnings;
use strict;
my $details = 'file2.txt';
my $old_details = 'file1.txt';
my %names;
open my $data, '<', $details or die $!;
while (<$data>)
{
my ($name, #ids) = split;
push #{ $names{$_} }, $name for #ids;
}
open my $old_data, '<', $old_details or die $!;
while (<$old_data>)
{
chomp;
print #{ $names{$_} // [$_] }, "\n";
}
Output:
FirstName:LastName:Location:Country:Old_ID
FirstName2:LastName2:Location2:Country2:Old_ID2
FirstName4:LastName4:Location4:Country4:Old_ID4
Expected output:
FirstName:LastName:Location:Country:ID
FirstName2:LastName2:Location2:Country2:ID2
FirstName4:LastName4:Location4:Country4:ID4

Answer 1

Just try this way:
use strict; # Use strict Pragma
use warnings;
my ($file1, $filecnt1, $file2, $filecnt2) = ""; #Declaring variables
$file1 = "a1.txt"; $file2 = "b1.txt"; #Sample files
readFileinString($file1, \$filecnt1); # Reading first file
readFileinString($file2, \$filecnt2); # Reading second file
$filecnt2=~s/\:Old\_ID/\:ID/g; # Replacing that difference content
my #firstfle = split "\n", $filecnt1; # Move content to array variable to compare
my #secndfle = split "\n", $filecnt2;
my %firstfle = map { $_ => 1 } #firstfle; #Mapping the array into hash variable
my #scdcmp = grep { $firstfle{$_} } #secndfle;
print join "\n", #scdcmp;
#---------------> File reading
sub readFileinString
#--------------->
{
my $File = shift;
my $string = shift;
open(FILE1, "<$File") or die "\nFailed Reading File: [$File]\n\tReason: $!";
read(FILE1, $$string, -s $File, 0);
close(FILE1);
}
#---------------> File Writing
sub writeFileinString
#--------------->
{
my $File = shift;
my $string = shift;
my #cDir = split(/\\/, $File);
my $tmp = "";
for(my $i = 0; $i < $#cDir; $i++)
{
$tmp = $tmp . "$cDir[$i]\\";
mkdir "$tmp";
}
if(-f $File){
unlink($File);
}
open(FILE, ">$File") or die "\n\nFailed File Open for Writing: [$File]\n\nReason: $!\n";
print FILE $$string;
close(FILE);
}