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.

Steps to use Zsh here-documents:

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.
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.

Run the script and inspect the expanded and literal output.

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

Use an unquoted delimiter only when script values should expand inside the block.
```
cat <<EOF
To: $recipient
Status: ready
EOF
```
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.
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.
Remove the sample script after testing.
```
$ rm -f heredoc-demo.zsh
```