Why is bash checking the syntax of my here document text?

Question

I have the following block of code in my file:

175 MY_IP=`ifconfig eno1 | grep netmask | tr -s ' ' | cut -d " " -f 3`  
176 echo ""  > /home/hadoop/.ssh/config  
177 cat > /home/hadoop/.ssh/config  <<EOF  
178 Host `echo $MY_IP | sed 's/.[0-9][0-9]*$//g'`.* 0.0.0.0 master   worker*  
179    StrictHostKeyChecking no  
180    UserKnownHostsFile=/dev/null  
181 EOF  

I expect lines 178 to 181 to just be written to a file, but I get this error output:

/script.sh: line 178: unexpected EOF while looking for matching `''
/script.sh: line 184: syntax error: unexpected end of file

Why is it not just copying that text instead of checking its syntax?

Update: The way my code and error messages look right now:

175 MY_IP=`ifconfig eno1 | grep netmask | tr -s ' ' | cut -d " " -f 3`  
176 echo ""  > /home/hadoop/.ssh/config  
177 cat > /home/hadoop/.ssh/config  <<EOF  
178 Host `echo $MY_IP | sed "s/.[0-9][0-9]*$//g"`.* 0.0.0.0 master worker*  
179    StrictHostKeyChecking no  
180    UserKnownHostsFile=/dev/null  
181 EOF  
182   
183 chown -R hadoop:hadoop /home/hadoop  

/script.sh: line 175: unexpected EOF while looking for matching `''
/script.sh: line 184: syntax error: unexpected end of file

Solved: After reviewing my code, I found a missing single quote in one of the very first lines. Pairing it with another solved the issue.

Answer 1

The shell will perform different kind of expansions (including command substitutions like your `echo ...`, but also variable and arithmetic expansions) inside here documents unless the delimiter is quoted.

Compare:

cat <<EOF
$$ $((2 + 3)) $(hostname) `date`
EOF
4502 5 fazq Mon Mar 11 23:03:27 EET 2019

vs:

cat <<'EOF'
$$ $((2 + 3)) $(hostname) `date`
EOF
$$ $((2 + 3)) $(hostname) `date`

Both double or single quotes will do in the last case.

Answer 2

From man bash:

Here Documents
This type of redirection instructs the shell to read input from the current source until a line containing only delimiter (with no trailing blanks) is seen. All of the lines read up to that point are then used as the standard input (or file descriptor n if n is specified) for a command.

Your EOF line, as currently posted in the question, contains trailing blanks. Remove them.

Answer 3

We don't have the whole script here, but note how the line number on the "unexpected EOF while looking for matching [single quote]" changes from 178 to 175 when you change the quotes inside the here-doc from single quotes to double quotes.

That hints to me that the actual issue, the unfinished quote, is somewhere before the snippet you posted.

For example, in the script below the actual error is obviously on the first line, but from the shell's point of view, the quoted string started there continues until the next quote, and so on, with the unpaired one being the one after bar (note how the syntax highlighting makes it evident that the second echo is quoted and foo and bar aren't):

$ cat quote.sh
echo 'error here

echo 'foo' 'bar'

$ bash quote.sh
quote.sh: line 3: unexpected EOF while looking for matching `''
quote.sh: line 4: syntax error: unexpected end of file

Changing the second echo command to echo "foo" "bar" would show the error on line 1, as that would then be the line where the final single-quoted string starts.

You'll need to look through your whole script more closely. Or just dump it to shellcheck.net, it will notice cases like this.