Adding backtick ( ` ) to heredoc output in shell command

Question

I need to add a cmd prompt modifier, PS1="..." within a shell script I am setting up. The issue is, I am using backtick to execute a command prior the main command:

sudo tee ~/.bashrc <<EOF

# Display absolute path in cmd line, cmds on new line
PS1='\[`[ $? = 0 ] && X=2 || X=1; tput setaf $X`\]\h [\u]\[`tput sgr0`\]:$PWD\n\$ '

EOF

cat ~/.bashrc gives:

# Display absolute path in cmd line, cmds on new line
PS1='\[\]\h [\u]\[\]:/Users/myuser/Library/Application Support/Sublime Text 3/Packages/User\n$ '

nano ~/bashrc gives:

PS1='\[^[[32m\]\h [\u]\[^[(B^[[m\]:/Users/myuser/Library/Application Support/Sublime Text 3/Packages/User\n$ '

This clearly means that everything in the backtick is not properly read. How can I escape the backtick or otherwise write line that includes a backtick to a file using shell?

Answer 1

In the here-document, as you've written it, the shell will do parameter expansion ($PWD will be expanded to the path of the current directory at the time of parsing the script, for example), command substitution (the "backticks" will be executed and whatever that command produces will be inserted in their place, at the time of parsing the here-document) and arithmetic expansion (none of that in your case).

If you don't want this, i.e. you want the contents of the here-document to be delivered as-is, then you can do this:

tee -a "$HOME/.bashrc" <<'EOF'

# contents of here-document here

EOF

The apostrophes around the EOF on the first line prevents the shell from expanding anything in the here-document itself.