• read file1 into a %hash
• * inside a loop
• ... read file2 line by $line
• ... split the $line to @fields at |
• ... if the first $fields[0] exists in the %hash , print the whole $line to file3

you'll need open , readline , chomp , split , exists , print and while loops for this.

i am actually new to scripting languages i didn't quite follow what you meant in step 2

pvighneshmufc:

He meant that the following lines are inside of a loop, like this:

# read file1 into a %hash
... code to do that here ...

# inside a loop
while (my $line = <$file2>) {
    # read file2 line by line
    ... this was done in the loop condition above ...

    # split the $line to @fields at |

    # if the first $fields[0] exists in the %hash,
        # print the whole $line to file 3
}
[download]

This is a relatively common question, so LanX gave you the outline of a good solution to the problem.

A frequent mistake is to try to read *both* files inside the loop, giving one of two bad outcomes:

• Either the first file is completely read in the first pass of the loop, so the code can only find a single match if it happens to be the first line in the second file, or
• the code re-opens the first file each time, and therefore can find all the matches, but runs extremely slowly⁽¹⁾ because it reads the first file completely for each line in the second file.

(1) Extremely slowly in the relative sense--for small files you may not notice it. But if your files get large enough, you'll wonder why such a fast computer is so freakin' slow.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

Perl read file line by line led me to

http://perlmaven.com/open-and-read-from-files

The first code example shows it already, though $line is named $row here.

I'm not going to give you complete code, because I want to help you to learn Perl. :)

Cheers Rolf
_{(addicted to the Perl Programming Language and ☆☆☆☆ :)
Wikisyntax for the Monastery}

See Files and I/O in perlintro.

use strict;
use warnings;
use Data::Dumper;
my $file1 = 'file1';
my $file2 = 'file2';
#reading file1 into a hash
my %hash=();
open (my $fh,'<',$file2) or die $!;
while(my $line=<$fh>)
{
chomp $line;
$hash{line}=1;
print Dumper %hash;
}
close $fh;

#reading file2 line by line
open (my $fh2,'<',$file1) or die $!;
while (my $row = <$fh2>) {
chomp $row;

my @fields = split(/\|/, $row);
print $row if exists $hash{$fields[0]};
}
close $fh2; ~

You have at least one bug of forgetting sigil $ in line once, but yes this was the basic idea.

And dumping inside the loop is costly.

Furthrmore you might want to use <code> tags next time. :)

Minor nitpick: when setting value 1, you don't need exists anymore. :)

Cheers Rolf
_{(addicted to the Perl Programming Language and ☆☆☆☆ :)
Wikisyntax for the Monastery}

#!/nairvigv/bin/perl
use strict;
use warnings;
use Data::Dumper;

my $file1 = 'BBIDs.txt';
my $file2 = 'fixedincomeTransparency.out.px.derived.updates';
#reading file1 into a hash

my %hash;
my @fields;
open (my $fh,'<',$file1) or die $!;
while(my $line=<$fh>)
{
chomp $line;
 next if $line =~ /^\s*$/;
 $hash{$line}=1;
}
#print Dumper(\%hash);

close $fh;



open (my ($fh2),$file2) or die $!;

while (my $row = <$fh2>)
 {
         chomp $row;

       print "$row\n";
         next if $row =~ /^\s*$/;
        my (@fields) = split(/\|/, $row);



print "$fields[0]\n ";




if (exists $hash{$fields[0]})
{
print "$row\n";
}
}


close $fh2;
~
[download]

Hello this works for a program with less lines i.e 10. However when i run it on a big file say about 700k lines nothing happens. Any idea what can be causing this?

Due to broken indentation it's hard to read and I won't go into details.

Have a look at http://perl.plover.com/FAQs/Buffering.html and basic debugging checklist

Cheers Rolf
_{(addicted to the Perl Programming Language and ☆☆☆☆ :)
Wikisyntax for the Monastery}

I am not sure if this is homework or not? If so, you should tell us.
However, I will give you some actual code.
I process text files frequently - Perl is great at this.
Skipping blank lines in the input is a normal "reflex reaction" by me and I show a common way to do that.

#!/usr/bin/perl
use warnings;
use strict;
use Inline::Files;

my %File1Hash;

while (my $line = <FILE1>)
{
    next if $line =~ /^\s*$/;  # skip blank lines
    $line =~ s/\s*$//; # remove all trailing space,
                       # including the line ending

    $File1Hash{$line}++;
}

while (my $line = <FILE2>)
{
    next if $line =~ /^\s*$/;  # skip blank lines
   
    my ($id) = split /\|/,$line;  # get the first field
    print $line if exists $File1Hash{$id};
}

=Prints
COA213345|a|b|c|
COA213345|a|b|c|
=cut

__FILE1__
COA213345
COA213345
COA213445
DOB213345
EOA213345

__FILE2__
COA213345|a|b|c|
COA213345|a|b|c|
LOA213345|a|b|c|
kOB213345|a|b|c|
LOA213345|a|b|c|
[download]