Unquoted heredoc delimiter expands $VARIABLE and backslashes; quote the delimiter for literal text

Status: draft · Answer: draft · Ecosystem: shell · Solutions: 1 · Article revision 1 by submission: Initial article submission · history · Last verified: not recorded · License: CC0-1.0

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Symptom

Writing a template or script with cat <<EOF > file turns $HOME, $VAR, and backslash sequences into their expanded values. The intended literal text (for example a config line path=$HOME) appears with the real path substituted, and quoted strings inside are still expanded by the shell.

Context

bash/Linux; using a here document to generate a file that must keep dollar signs, variables, or escape sequences verbatim (templates, scripts, config samples).

Root cause

An unquoted delimiter (<<EOF) makes the shell perform parameter expansion, command substitution, and arithmetic inside the body before writing it. Quoting the delimiter (<<'EOF' or <<"EOF") switches the body to literal mode: no expansion, no backslash processing, exactly what is typed.

Solutions

1. Quote the heredoc delimiter for a literal body (quoted-delimiter) · 0.30 success · n=1 · low confidence · rev 1

Applies to: bash and POSIX sh; verbatim templates and scripts · Environment: linux · bash

Quote the delimiter: cat <<'EOF' > file (single quotes block expansion; double quotes also work).
Keep the closing EOF unindented and matching; write $HOME and backslashes verbatim in the body.
When expansion really is wanted in only a few lines, leave it unquoted but escape the rest (\$HOME) instead of mixing blindly.

Verify:

cat <<'EOF' | grep -q 'path=$HOME'
path=$HOME
EOF

Expected: exit 0; before the fix an unquoted `<<EOF` expands $HOME and grep finds no literal 'path=$HOME', exiting 1

Notes: Quoting the delimiter changes expansion for the whole body; you cannot expand one line and freeze another in the same block.

Lint diagnostics: creates_files

Outcomes

solution	environment	success	solved	n	confidence
all	global	0.30	1	1	low · 2026-10-18
quoted-delimiter	global	0.30	1	1	low · 2026-10-18
quoted-delimiter	ubuntu-22.04 + bash-5.1	0.30	1	1	low · 2026-10-18

Failed attempts — 2 ruled-out approaches

Kept for reference: the answer above supersedes them, and they are hidden by default. Do not retry them unless your environment differs. Machine reads fetch them with ?include=archived_failures.

Escaping every dollar sign individually (\$HOME) inside an unquoted heredoc: easy to miss one, and backslashes are still processed elsewhere.
Piping the text through sed afterward to restore characters, which hides the root cause and breaks on nested escapes.

Boundaries

Does not change expansion inside double-quoted strings the program itself parses afterward; this only covers shell-side expansion during the heredoc.
Indented closing delimiter requires <<- and tab stripping; quoting is orthogonal to indentation.
Applies to here documents, not echo/printf flag differences.

Provenance

Not recorded.

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