Multi-Lines Text

Echo Command#

Using the -e option can create simple multi-line text.

echo -e 'aa\nbb'

aa
bb

Here Document#

Here Document (abbreviated as Heredoc) is a way of input redirection in Shell, allowing you to embed multi-line text within scripts or commands and pass it to commands or files.

Basic Syntax#

command <<EOF
Multi-line text content
EOF

• command：such as cat, sed, gawk.
• <<EOF：marks the beginning of the document and defines the end marker.
• EOF：marks the end position of the document.

Here, EOF is just an example, and any marker can be used.

Multi-Line Text File#

Multi-line text can be redirected to the foo.txt file.

cat <<EOF > foo.txt
apple
banana
EOF

cat foo.txt

apple
banana

As Input to a Command#

grep 'app' <<EOF
apple
banana
EOF

Difference of Quotes#

If the EOF marker is used with quotes, the function will be different.

If the content is just a pure document, try to use quotes to reduce the impact of special characters.

Using Quotes#

Single/double quotes are the same, and neither will interpret the $ symbol.

cat <<'EOF'
$HOME
EOF

$HOME

Not Using Quotes#

And not using quotes is the same, and will interpret the $ symbol.

cat <<EOF
$HOME
EOF

/home/kuga