regex - How to merge diff result between two files into a third file? -

i trying write perl script following: compare 2 files same name different source dirs, meaning:

diff source_dir_1/file_1 source_dir_2/files_2 

and each changed line in file_2 (compared file_1) find line file_1 (that has been changed in file_2) @ third file: source_dir_3/file_3, , replace line line file_2.

for example, for:

file_1:

my name shahar
hello world
nice meet

file_2

my name shahar
goodbye world
nice meet

file_3:

this line can different
hello world
nice meet

the resulting file_3 be:

file_3_after_script:

this line can different
goodbye world
nice meet

i'm having problem writing it, because sometime 1 line in file_1 replaced several lines in file_2,

do have suggestions how should approach problem?

your goal unclear. include code you've tried in question on so.

nevertheless, of course possible open 3 files simultaneously , perform logic on them.

the following shows best interpretation of goal. cycles through lines of each file, , prints line file2 if file1 , 2 different, otherwise prints file3.

use strict; use warnings; use autodie;  $file1 = '...'; $file2 = '...'; $file3 = '...';  #open $fh1, '<', $file1; #open $fh2, '<', $file2; #open $fh3, '<', $file3; # open strings temporarily make script self-contained: open $fh1, '<', \ "my name shahar\nhello world\nnice meet\n"; open $fh2, '<', \ "my name shahar\ngoodbye world\nnice meet\n"; open $fh3, '<', \ "this line can different\nhello world\nnice meet\n";  while (! grep eof $_, $fh1, $fh2, $fh3) {     $line1 = <$fh1>;     $line2 = <$fh2>;     $line3 = <$fh3>;      print $line1 ne $line2 ? "file2: $line2" : "file3: $line3"; }  print "file3: $_" while (<$fh3>); # print rest of file (if any) 

outputs:

file3: line can different file2: goodbye world file3: nice meet