How to avoid heredoc expanding variables? [duplicate]

Question

I'm trying to create a script file using substitution string from ENV but want also to prevent some from escaping

export PLACEHOLDER1="myPlaceholder1Value" sudo /bin/su -c "cat << EOF > /etc/init.d/my-script #!/bin/bash  myvariable_1=toto$PLACEHOLDER1 myvariable_final=\"dynamicvar=\${myvariable_1},\${myvariable_2}\" EOF " 

It results in which is not good as the myvariable_final are not escaped and substituted as the one from the init script dependencies ($remote_fs, $syslog, $network, $time)

#!/bin/bash  myvariable_1=totomyPlaceholder1Value myvariable_2=titimyPlaceholder2Value myvariable_final="dynamicvar=," 

---

If i try to put a backslash \ behind the dollars $, I manage to avoid the substitution but I getting an unwanted backslash \:

export PLACEHOLDER1="myPlaceholder1Value" export PLACEHOLDER2="myPlaceholder2Value" sudo /bin/su -c "cat << EOF > /etc/init.d/my-script #!/bin/bash  myvariable_1=toto$PLACEHOLDER1 myvariable_2=titi$PLACEHOLDER2 myvariable_final=\"dynamicvar=\$\{myvariable_1},\$\{myvariable_2}\" EOF " 

results in:

#!/bin/bash  myvariable_1=totomyPlaceholder1Value myvariable_2=titimyPlaceholder2Value myvariable_final="dynamicvar=$\{myvariable_1},$\{myvariable_2}" 

---

Wanted/attended result whould have been :

#!/bin/bash  myvariable_1=totomyPlaceholder1Value myvariable_2=titimyPlaceholder2Value myvariable_final="dynamicvar=${myvariable_1},${myvariable_2}" 

solved by putting quote around the EOF as below and using backslash to control the escaping when needed

export PLACEHOLDER1="myPlaceholder1Value" export PLACEHOLDER2="myPlaceholder2Value" sudo /bin/su -c "cat << 'EOF' > /etc/init.d/my-script #!/bin/bash  myvariable_1=toto$PLACEHOLDER1 myvariable_2=titi$PLACEHOLDER2 myvariable_final=\"dynamicvar=\${myvariable_1},\${myvariable_2}\" EOF " 

Answer 1

Just use 'EOF' to prevent the variable from expanding:

sudo /bin/su -c "cat << 'EOF' > /etc/init.d/my-script #                       ^   ^ 

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 for a command.

The format of here-documents is:

      <<[-]word               here-document       delimiter 

No parameter expansion, command substitution, arithmetic expansion, or pathname expansion is performed on word. If any characters in word are quoted, the delimiter is the result of quote removal on word, and the lines in the here-document are not expanded. If word is unquoted, all lines of the here-document are subjected to parameter expansion, command substitution, and arithmetic expansion. In the latter case, the character sequence \<newline> is ignored, and \ must be used to quote the characters \, $, and `.

Answer 2

when using the su command put the command itself in sigle quotes and just escape the $ with a backslash. the placeholder variables has to set in command bash context (here after su). so you need to do sth like

su -c 'ph="ph"; cat << EOF > script  varinscript=$ph var=\${var} EOF'