sudo apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
2 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] y
Setting up grub-pc (2.02-2ubuntu8.6) ...
/var/lib/dpkg/info/grub-pc.config: 34: /etc/default/grub: Syntax error: EOF in backquote substitution
dpkg: error processing package grub-pc (--configure):
 installed grub-pc package post-installation script subprocess returned error exit status 2
Setting up linux-image-4.15.0-36-generic (4.15.0-36.39) ...
Processing triggers for linux-image-4.15.0-36-generic (4.15.0-36.39) ...
/etc/kernel/postinst.d/initramfs-tools:
update-initramfs: Generating /boot/initrd.img-4.15.0-36-generic
/etc/kernel/postinst.d/zz-update-grub:
/usr/sbin/grub-mkconfig: 34: /etc/default/grub: Syntax error: EOF in backquote substitution
run-parts: /etc/kernel/postinst.d/zz-update-grub exited with return code 2
dpkg: error processing package linux-image-4.15.0-36-generic (--configure):
 installed linux-image-4.15.0-36-generic package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
 grub-pc
 linux-image-4.15.0-36-generic
E: Sub-process /usr/bin/dpkg returned an error code (1)