Activating error 503 from a shell script

During deployment of a new version of a website you might want to have your server returning an error 503 (temporarily unavailable). You can easily do this by pointing your web folder to a php page that contains this:

//server_down.php
header("HTTP/1.1 503 Service Unavailable");
echo "We are deploying a new version of NoSoapNoBubbles, the server is going to be down for a minute.";

if your webfolder is linked to another folder with a symlink (as I explained in my previous post symfony project on bluehost shared hosting) then you can just remove the link and add a new one pointing to the folder containing server_down.php. Remember to rename server_down.php index.php or to create an .htaccess file containing

DirectoryIndex server_down.php

so that server_down.php is shown as directory index.

This solution is more than fine, but I needed to access some files during deployment so I decided to use a combination of the approach above and .htaccess. When the web directory (of our dev site) is being wiped out, then I redirect using the link, when the directory is filled but I’m running DB tasks I redirect using .htaccess.

Since our deploy tasks are fully automated (happen on svn commit) here how to edit the .htaccess file using SED (stream editor).
Activate redirection:

if [ "$#" != "1" ]; then
  echo Invalid number of arguments, must be 1. >&2
  exit 1
fi
#
HTACCESSPATH=$1 #path to the .htaccess file
cp  $HTACCESSPATH/.htaccess $HTACCESSPATH/.htaccessTMP
sed 's|#*RewriteCond %{REQUEST_URI} !server_down.php$|RewriteCond %{REQUEST_URI} !server_down.php$|' $HTACCESSPATH/.htaccessTMP > TMPFILE && mv TMPFILE $HTACCESSPATH/.htaccessTMP
sed 's|#*RewriteCond %{REQUEST_URI} !always_available.php$|RewriteCond %{REQUEST_URI} !always_available.php$|' $HTACCESSPATH/.htaccessTMP > TMPFILE && mv TMPFILE $HTACCESSPATH/.htaccessTMP
sed 's|#*RewriteRule ^(.*)$ /server_down.php [L]|RewriteRule ^(.*)$ /server_down.php [L]|' $HTACCESSPATH/.htaccessTMP > TMPFILE && mv TMPFILE $HTACCESSPATH/.htaccessTMP
mv $HTACCESSPATH/.htaccessTMP $HTACCESSPATH/.htaccess
Deactivate redirection:if [ "$#" != "1" ]; then
  echo Invalid number of arguments, must be 1. >&2
  exit 1
fi
#
HTACCESSPATH=$1
cp  $HTACCESSPATH/.htaccess $HTACCESSPATH/.htaccessTMP
sed 's|RewriteCond %{REQUEST_URI} !server_down.php$|#RewriteCond %{REQUEST_URI} !server_down.php$|' $HTACCESSPATH/.htaccessTMP > TMPFILE && mv TMPFILE $HTACCESSPATH/.htaccessTMP
sed 's|RewriteCond %{REQUEST_URI} !always_available.php$|#RewriteCond %{REQUEST_URI} !always_available.php$|' $HTACCESSPATH/.htaccessTMP > TMPFILE && mv TMPFILE $HTACCESSPATH/.htaccessTMP
sed 's|RewriteRule ^(.*)$ /server_down.php [L]|#RewriteRule ^(.*)$ /server_down.php [L]|' $HTACCESSPATH/.htaccessTMP > TMPFILE && mv TMPFILE $HTACCESSPATH/.htaccessTMP
mv $HTACCESSPATH/.htaccessTMP $HTACCESSPATH/.htaccess