Comparing lines in a file with perl - perl

Question

Ive been trying to compare lines between two files and matching lines that are the same.
For some reason the code below only ever goes through the first line of 'text1.txt' and prints the 'if' statement regardless of if the two variables match or not.
Thanks
use strict;
open( <FILE1>, "<text1.txt" );
open( <FILE2>, "<text2.txt" );
foreach my $first_file (<FILE1>) {
foreach my $second_file (<FILE2>) {
if ( $second_file == $first_file ) {
print "Got a match - $second_file + $first_file";
}
}
}
close(FILE1);
close(FILE2);

Answer 1

If you compare strings, use the eq operator. "==" compares arguments numerically.

Answer 2

Here is a way to do the job if your files aren't too large.
#!/usr/bin/perl
use Modern::Perl;
use File::Slurp qw(slurp);
use Array::Utils qw(:all);
use Data::Dumper;
# read entire files into arrays
my #file1 = slurp('file1');
my #file2 = slurp('file2');
# get the common lines from the 2 files
my #intersect = intersect(#file1, #file2);
say Dumper \#intersect;

Answer 3

A better and faster (but less memory efficient) approach would be to read one file into a hash, and then search for lines in the hash table. This way you go over each file only once.
# This will find matching lines in two files,
# print the matching line and it's line number in each file.
use strict;
open (FILE1, "<text1.txt") or die "can't open file text1.txt\n";
my %file_1_hash;
my $line;
my $line_counter = 0;
#read the 1st file into a hash
while ($line=<FILE1>){
chomp ($line); #-only if you want to get rid of 'endl' sign
$line_counter++;
if (!($line =~ m/^\s*$/)){
$file_1_hash{$line}=$line_counter;
}
}
close (FILE1);
#read and compare the second file
open (FILE2,"<text2.txt") or die "can't open file text2.txt\n";
$line_counter = 0;
while ($line=<FILE2>){
$line_counter++;
chomp ($line);
if (defined $file_1_hash{$line}){
print "Got a match: \"$line\"
in line #$line_counter in text2.txt and line #$file_1_hash{$line} at text1.txt\n";
}
}
close (FILE2);

Answer 4

You must re-open or reset the pointer of file 2. Move the open and close commands to within the loop.
A more efficient way of doing this, depending on file and line sizes, would be to only loop through the files once and save each line that occurs in file 1 in a hash. Then check if the line was there for each line in file 2.

Answer 5

If you want the number of lines,
my $count=`grep -f [FILE1PATH] -c [FILE2PATH]`;
If you want the matching lines,
my #lines=`grep -f [FILE1PATH] [FILE2PATH]`;
If you want the lines which do not match,
my #lines = `grep -f [FILE1PATH] -v [FILE2PATH]`;

Answer 6

This is a script I wrote that tries to see if two file are identical, although it could easily by modified by playing with the code and switching it to eq. As Tim suggested, using a hash would probably be more effective, although you couldn't ensure the files were being compared in the order they were inserted without using a CPAN module (and as you can see, this method should really use two loops, but it was sufficient for my purposes). This isn't exactly the greatest script ever, but it may give you somewhere to start.
use warnings;
open (FILE, "orig.txt") or die "Unable to open first file.\n";
#data1 = ;
close(FILE);
open (FILE, "2.txt") or die "Unable to open second file.\n";
#data2 = ;
close(FILE);
for($i = 0; $i < #data1; $i++){
$data1[$i] =~ s/\s+$//;
$data2[$i] =~ s/\s+$//;
if ($data1[$i] ne $data2[$i]){
print "Failure to match at line ". ($i + 1) . "\n";
print $data1[$i];
print "Doesn't match:\n";
print $data2[$i];
print "\nProgram Aborted!\n";
exit;
}
}
print "\nThe files are identical. \n";

Answer 7

Taking the code you posted, and transforming it into actual Perl code, this is what I came up with.
use strict;
use warnings;
use autodie;
open my $fh1, '<', 'text1.txt';
open my $fh2, '<', 'text2.txt';
while(
defined( my $line1 = <$fh1> )
and
defined( my $line2 = <$fh2> )
){
chomp $line1;
chomp $line2;
if( $line1 eq $line2 ){
print "Got a match - $line1\n";
}else{
print "Lines don't match $line1 $line2"
}
}
close $fh1;
close $fh2;
Now what you may really want is a diff of the two files, which is best left to Text::Diff.
use strict;
use warnings;
use Text::Diff;
print diff 'text1.txt', 'text2.txt';