How to compare two files in Linux

Question: I have two scripts in a directory on my server. One is the right one and one is not, but I do not remember which is which. How can I compare the two files?

Answer: Linux and UNIX-like operating systems usually come with a comparison command called “diff”. This command will display line-by-line differences between two files. It is useful for software developers, but web developers and web application managers will find it useful as well.

To use it, just enter:

diff script1.php script2.php

It will search through both PHP scripts and find any lines that are different. The output will look something like this:

if(!function_exists('add_action')){
header('HTTP/1.0 404 Not Found');
header('Location: ../../');
> exit();
}

In the first file “exit();” is not present, while the second file correctly contains it. Tomorrow we will learn how to merge the two differing files into one correct file.