How to insert a line into text document right before line containing some text in bash?

Question

I have a variable say $strToInsert I have a file file.html I wonder how to find last appearence of </head> and insert a new line before line with it and fill it with $strToInsert contents?

Update:

Here is what I have:

GACODE="UA-00000000-1"

if [ "$2" = "" ]
then
    echo "Usage: $0 <url to extract doxygen generated docs into> <GA tracker code if needed>"
    echo "Using default"
else
    GACODE = $2
fi

GASTR="<script>var _gaq = _gaq || [];_gaq.push([\'_setAccount\', \'$GACODE\']);_gaq.push([\'_trackPageview\']);(function() {var ga = document.createElement('script'); ga.type = 'text/javascript\'; ga.async = true;ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);})();</script>"

but when I try

sed -i 's#</head>#'$GASTR'\n</head>#' header.html

I get:

sed: -e expression #1, char 21: unterminated `s' command

Whats wrong with my code?

Answer 1

sed -i "s#</head>#$strToInsert\n</head>#" file.html

but I'm not sure is "last appearence" means you can have several </head> in your file?

Answer 2

sed "/<\/head>/i\
$strToInsert" file.html

This will insert the new line before every </head>, but why do you have more than one?

Answer 3

cat "$file" #(before)
1
2 </head>
3
4 </head>
5
6 </head>

---

strToInsert="hello world"
lnum=($(sed -n '/<\/head>/=' "$file"))  # make array of line numbers
((lnum>0)) && sed -i "${lnum[$((${#lnum[@]}-1))]}i \
                      $strToInsert" "$file"

---

cat "$file" #(after)
1
2 </head>
3
4 </head>
5
hello world
6 </head>