Sed substituiton for string containing both spaces and double quotes

Question

I'm trying to use sed in a script to modify a line in my grub configuration file(/boot/grub/grub.cfg) each time grub updates. I wish to replace the following line:

menuentry "Kali GNU/Linux"

with this:

'menuentry "Kali GNU/Linux" --class kali'

The line in /boot/grub/grub.cfg is as follows:

menuentry "Kali GNU/Linux" --class gnu-linux --class os $menuentry_id_option 'osprober-gnulinux-/boot/vmlinuz-5.14.0-kali2-amd64--7afb9c25-9d47-4ce4-a3dd-635aa0b04d7a'

Basically, what I want to do is add the line --class kali. I cannot replace gnu-linux or os with kali as those words occur multiple times.

The script I've used is as follows:

TARGET_STRING='menuentry "Kali GNU/Linux"'
NEW_STRING='menuentry "Kali GNU/Linux" --class kali'
sudo sed -i "s/$TARGET_STRING/$NEW_STRING/g" /boot/grub/grub.cfg

This fails to work, giving the following error:

sed: -e expression #1, char 32: unknown option to `s'

I've found solutions online for substituting a string containing spaces here and substituting a string containing double quotes here, but not when a string contains both.

Could someone please help me out?

Note: I am using GNU sed 4.7

Answer 1

There is no need for variables. Just use the strings directly:

sudo sed -i 's|menuentry "Kali GNU/Linux"|menuentry "Kali GNU/Linux" --class kali|' /boot/grub/grub.cfg

You are getting the errors because your strings contain / and you were using / as the separator in the s/// operator. You can use any character for that though, which is why I am using s||| above. In general, you need to be sure to pick a character that is not present in either the $target_string or the $new_string. So | works in this example, but you might need to pick another one for other cases.

You can use variables if you really, really want to, they're just not helping here. Also, as a general rule, it is better to avoid CAPITAL variable names in shell scripts. This would work though:

target_string='menuentry "Kali GNU/Linux"'
new_string='menuentry "Kali GNU/Linux" --class kali'
sudo sed -i "s|$target_string|$new_string|" /boot/grub/grub.cfg