Avoid infinite loop with 301 redirects - .htaccess

Question

I'm using .htaccess to redirect
http://www.example.com/foo/
to
http://www.example.com/foo/bar
This is my code:
redirect 301 /foo/ http://www.example.com/foo/bar
However this produces a feedback loop, something like
http://www.example.com/foo/barbarbarbarbarbar etc.
I've tried placing delimiters around it:
redirect 301 ^/foo/$ http://www.example.com/foo/bar
but then the redirect simply doesn't take place. I'm probably missing some very simple point of syntax. Any ideas? Thanks.
EDIT
Here's my (almost) full .htaccess file:
RewriteEngine On
RewriteBase /
# Canonical is www version
RewriteCond %{HTTP_HOST} !^www.example.com$ [NC]
RewriteRule ^(.*)$ http://www.example.com/$1 [L,R=301]
#redirect => http unless special page
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{HTTPS} on
RewriteCond %{REQUEST_URI} !^/(javascripts|images|library|stylesheets)
RewriteRule ^(.*)$ http://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
#redirect => https for special pages
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
# send to router
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php [L]

Answer 1

Have your rules like this:
RewriteEngine On
RewriteBase /
# Canonical is www version
RewriteCond %{HTTP_HOST} !^www\.example\.com$ [NC]
RewriteRule ^ http://www.example.com%{REQUEST_URI} [L,R=301]
#redirect => http unless special page
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{HTTPS} on
RewriteCond %{THE_REQUEST} !/(javascripts|images|library|stylesheets)
RewriteRule ^(.*)$ http://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
#redirect => https for special pages
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{HTTPS} off
RewriteRule !^index\.php$ https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
RewriteRule ^foo/?$ /foo/bar [L,NC,R=301]
# send to router
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^ index.php [L]
make sure to test this in a new browser or clear your browser cache before testing.

Answer 2

For your information, it really depends on your hosting provider. It may be behind a Load Balancer and you don't have the proper env var set (like HTTPS and others...).
In my case (Infomaniak), nothing actually worked and I got infinite redirect loop.
The right way to do this for Infomaniak is actually explained in their support site:
RewriteEngine on
RewriteCond %{HTTP:X-Forwarded-Proto} !https
RewriteRule (.*) https://your-domain.com/$1 [R=301,L]
So, always check with your hosting provider. Hopefully they have an article explaining how to do this. Otherwise, just ask the support.

Answer 3

It depends on what is the resource that you want to expose with your redirect.
Is it a file or a directory.
if you would expose a directory under bar you should try :
RedirectMatch 301 ^/foo/ http://www.example.com/foo/bar/
if you would redirect to a file you should use this syntax :
redirect 301 /foo http://www.example.com/foo/bar
you can see this post for more informations

Answer 4

Instead of using redirect, you can use passthrough.
RewriteRule ^/foo$ /foo/bar [PT]