What does the below mentioned code do in .htaccess? - .htaccess

Question

Could anyone please tell me what the below code does?
RewriteEngine On
RewriteCond %{HTTP_HOST} ^example-old.com$
RewriteRule (.*) http://www.example-new.com/$1 [R=301,L]
Does it work only if someone types exactly example-old.com? What would happen to the URLs with folders, like example-old.com/folder1 and example-old.com/folder1/sub1/page1.php
One of my client's website has become a disaster. Following is the code in .htaccess and pages on Google search when opened, it adds an extra '/' at the end of every URL which displays a horrendous page. I am unable to figure out where the error in code is:
Options -Indexes
RewriteEngine On
RewriteCond %{HTTP_HOST} ^example-old.com$
RewriteRule (.*) http://www.example-new.com/$1 [R=301,L]
RewriteCond %{HTTP_HOST} ^www.example-old.com$
RewriteRule (.*) http://www.example-new.com/$1 [R=301,L]
RewriteCond %{HTTP_HOST} ^example-new.com$
RewriteRule (.*) http://www.example-new.com/$1 [R=301,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . index.php [L]
# remove browser bugs
BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0[678] no-gzip
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
Header append Vary User-Agent
RewriteCond %{HTTP_HOST} ^example-old\.com$ [OR]
RewriteCond %{HTTP_HOST} ^www\.example-old\.com$
RewriteRule ^2015\/?(.*)$ "http\:\/\/www\.example-old\.com\/$1" [R=301,L]
Instead of opening a page with the URL:-
http://www.example-new.com/folder1/page1.php
It opens:
http://www.example-new.com/folder1/page1.php/
I'm using example-old and example-new due to security reasons. Please help...!

Answer 1

RewriteEngine On
RewriteCond %{HTTP_HOST} ^example-old.com$
RewriteRule (.*) http://www.example-new.com/$1 [R=301,L]
This permanently redirects example.com/foo/foobar to example-new.com/foo/foobar
RewriteCond %{HTTP_HOST} ^example-old.com$
RewriteRule (.*) http://www.example-new.com/$1 [R=301,L]
in php context, you would use
if(host == "example.com" and Request_uri== "any request")
{header('location : host/Request_uri',301)
else
{no redirection}