Comparing two strings line by line in Perl - arrays

Question

I am looking for code in Perl similar to
my #lines1 = split /\n/, $str1;
my #lines2 = split /\n/, $str2;
for (int $i=0; $i<lines1.length; $i++)
{
if (lines1[$i] ~= lines2[$i])
print "difference in line $i \n";
}
To compare two strings line by line and show the lines at which there is any difference.
I know what I have written is mixture of C/Perl/Pseudo-code. How do I write it in the way that it works on Perl?

Answer 1

What you have written is sort of ok, except you cannot use that notation in Perl lines1.length, int $i, and ~= is not an operator, you mean =~, but that is the wrong tool here. Also if must have a block { } after it.
What you want is simply $i < #lines1 to get the array size, my $i to declare a lexical variable, and eq for string comparison. Along with if ( ... ) { ... }.
Technically you can use the binding operator to perform a string comparison, for example:
"foo" =~ "foobar"
But it is not a good idea when comparing literal strings, because you can get partial matches, and you need to escape meta characters. Therefore it is easier to just use eq.
Using C-style for loops is valid, but the more Perl-ish way is to use this notation:
for my $i (0 .. $#lines1)
Which will iterate over the range 0 to the max index of the array.

Answer 2

Perl allows you to open filehandles on strings by using a reference to the scalar variable that holds the string:
open my $string1_fh, '<', \$string1 or die '...';
open my $string2_fh, '<', \$string2 or die '...';
while( my $line1 = <$string1_fh> ) {
my $line2 = <$string2_fh>;
....
}
But, depending on what you mean by difference (does that include insertion or deletion of lines?), you might want something different.
There are several modules on CPAN that you can inspect for ideas, such as Test::LongString or Algorithm::Diff.

Answer 3

my #lines1 = split(/^/, $str1);
my #lines2 = split(/^/, $str2);
# splits at start of line
# use /\n/ if you want to ignore newline and trailing spaces
for ($i=0; $i < #lines1; $i++) {
print "difference in line $i \n" if (lines1[$i] ne lines2[$i]);
}

Answer 4

Comparing Arrays is a way easier if you create a Hashmap out of it...
#Searching the difference
#isect = ();
#diff = ();
%count = ();
foreach $item ( #array1, #array2 ) { $count{$item}++; }
foreach $item ( keys %count ) {
if ( $count{$item} == 2 ) {
push #isect, $item;
}
else {
push #diff, $item;
}
}
#Output
print "Different= #diff\n\n";
print "\nA Array = #array1\n";
print "\nB Array = #array2\n";
print "\nIntersect Array = #isect\n";
Even after spliting you could compare them as Array.