Using goto LABEL for comparing two files - perl

Question

I am unable to get desired output.
Please help to correct my errors.
file1
A
B
C
D
E
F
file2
A
D
C
Desired Output (if found print '1' at relative position in larger file and if not print '0')
1
0
1
1
0
0
code
#!/usr/bin/perl -w
open(FH,$file);
#q=<FH>;
open(FH1,$file2);
#d=<FH1>;
open(OUT,">out.txt");
foreach $i(#q) {
foreach $j(#d) {
if ($i eq $j) {
$id=1 ;
goto LABEL;
} elsif ($i ne $j) {
$id=1;
goto LABEL;
}
}
}
print OUT "1\t";
LABEL:
print OUT "0\t";
}
close FH;
close FH1;
close OUT;
note: actual files are much much larger and contain uneven number of elements.

Answer 1

You were looking for
for $q (#q) {
my $found = 0;
for $d (#d) {
if ($q eq $d) {
$found = 1;
goto LABEL;
}
}
LABEL: print "$found\n";
}
The above is better written as follows:
for $q (#q) {
my $found = 0;
for $d (#d) {
if ($q eq $d) {
$found = 1;
last;
}
}
print "$found\n";
}
But those solutions perform poorly. You can avoid iterating over #d repeatedly by using a hash.
my %d = map { $_ => 1 } #d;
for $q (#q) {
print $d{$q} ? "1" : "0", "\n";
}

Answer 2

Consider the following approach:
use strict;
use warnings;
use autodie;
use feature 'say';
open my $fh1, '<', 'file1';
open my $fh2, '<', 'file2';
say <$fh1> eq <$fh2> ? '1' : '0'
until eof $fh1 or eof $fh2;
Notes:
use strict; use warnings; to maintain sanity
autodie to take care of failed file opens
Lexical filehandles are preferred to bareword filehandles
say for syntactic sugar to automatically append a newline at the end of every 1 or 0
Diamond operator to read in each filehandle line-by-line
eq to string-compare the two lines
Ternary operator (COND ? TRUE : FALSE) to decide whether to print 1 or 0
until is a negated while
eof to tell the loop when either of the two filehandles has been exhausted

Answer 3

As it was said don't use LABEL. And to be honest you don't need perl for that, because join and sed do the job (may be you need to sort the files first):
join -a1 -a2 -e "0" -o 2.1 file1.txt file2.txt | sed "s/[^0]/1/g"
May be you need to sort your files first - in this case have a look at this post: comparing to unsorted files.

Answer 4

To be honest LABEL is not your friend - don't do that. For me it sounds more like a job for the join. But if you want to solve it using Perl I would try the following:
If the input files are sorted (otherwise you can use sort to achieve that) compare them line by line and print the result:
while ($line_from_f1 = <F1>)
{
$line_from_f2=<F2>;
if ($line_from_f1 eq $line_from_f2)
{
print "1\n";
}
else
{
print "0\n";
}
}
Shorter version (untested):
while (<F1>)
{
print ($_ eq <F2>)."\n";
}
Note: These versions compare the files line by line - if a line is missing in the middle it does not work properly.