Interview › Scripting (Bash, Groovy)
What is a here-document, and when would you use one? [Intermediate]
Answer
A here-document feeds a block of text to a command's stdin. I use it for generating config files, sending multi-line SQL, templating small files, or passing scripts to remote commands.
Technical explanation
With <<EOF, variables inside the heredoc are expanded by the shell.
With <<'EOF', the content is literal and variables are not expanded, which is safer for templates containing dollar signs.
Use <<-EOF to allow leading tab indentation to be stripped, but spaces are not stripped.
Hands-on example
cat > app.conf <<EOF
app_name=orders
port=8080
env=${ENVIRONMENT:-dev}
EOF
psql "$DATABASE_URL" <<'SQL'
select now();
select count(*) from users;
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