printf and Here Documents

printf: precise output

echo is fine for simple messages, but its options vary between systems. printf formats output precisely and portably:

printf "Hello, %s!\n" "Ada"
printf "%-10s|%5d|%8.2f\n" "keyboard" 3 89.5
printf "%-10s|%5d|%8.2f\n" "monitor" 12 249.99
printf "%s\n" apple banana cherry
printf "%03d\n" 7

Hello, Ada!
keyboard  |    3|   89.50
monitor   |   12|  249.99
apple
banana
cherry
007

• %s text, %d integer, %f decimal (%.2f with two places), %% a literal percent sign.
• A number sets the width; - left-aligns.
• \n must be written explicitly — printf doesn't add a newline.
• If there are more arguments than placeholders, the format is reused — which is how printf "%s\n" a b c prints one per line.

Here documents

A here document feeds multi-line text into a command:

name="Ada"
cat <<EOF
Dear $name,
Your order total is \$120.
EOF

cat <<'EOF'
Variables like $name are NOT expanded here.
EOF

Dear Ada,
Your order total is $120.
Variables like $name are NOT expanded here.

• With <<EOF, variables and $(...) are expanded.
• With <<'EOF' (quoted), the text is taken literally — ideal for writing scripts or config files that contain $.
• <<-EOF strips leading tab characters, so the text can be indented inside functions.

Generating files

service="api"
port=8080
cat > "$service.conf" <<EOF
[$service]
listen = 0.0.0.0:$port
workers = $(( 2 * 2 ))
EOF
cat api.conf

[api]
listen = 0.0.0.0:8080
workers = 4

Here strings

<<< passes a single string as input:

wc -w <<< "how many words are here"
tr 'a-z' 'A-Z' <<< "shout"

5
SHOUT