How to use here-documents in Zsh

Here-documents let a Zsh script feed a readable multiline block to a command without keeping that text in a separate input file. They fit small generated messages, short configuration fragments, SQL batches, and templates that should stay visible inside the script.

The <<WORD redirection starts the block, and a later line containing only WORD ends it. An unquoted delimiter lets Zsh expand parameters and command substitutions inside the block, while a quoted delimiter leaves the document text literal.

The sample script uses one unquoted delimiter for an expanded message and one quoted delimiter for a literal template. Checking it with zsh -n catches mismatched delimiters before the script runs. Keep each closing delimiter alone on its line, because spaces or other characters after it prevent Zsh from finding the end of the block.

1. Create a script that sends two here-document blocks to cat.

   heredoc-demo.zsh

   #!/usr/bin/env zsh
   emulate -L zsh
   setopt err_exit
    
   recipient=operations
   cat <<MESSAGE
   To: $recipient
   Status: ready
   MESSAGE
    
   cat <<'LITERAL'
   Literal example: $recipient
   LITERAL

   The first block uses <<MESSAGE, so $recipient expands. The second block uses <<'LITERAL', so the same text stays literal.

2. Check the script syntax.

   $ zsh -n heredoc-demo.zsh

   No output means Zsh parsed the here-document delimiters and the rest of the script without a syntax error.

3. Run the script and inspect the expanded and literal output.

   $ zsh heredoc-demo.zsh
   To: operations
   Status: ready
   Literal example: $recipient

4. Use an unquoted delimiter only when script values should expand inside the block.

   cat <<EOF
   To: $recipient
   Status: ready
   EOF

5. Quote the delimiter when the text contains shell syntax that must stay unchanged.

   cat <<'EOF'
   Literal example: $recipient
   EOF

   Do not indent the closing delimiter with spaces. Zsh only treats a line containing the delimiter word itself as the end of a plain << here-document.

6. Use «- only when the body and closing delimiter are indented with tab characters.

   Zsh strips leading tabs with «-, but it does not strip spaces. Use plain « when an editor might convert tabs to spaces.

7. Remove the sample script after testing.

   $ rm -f heredoc-demo.zsh