Heredocs

Heredocs allow you to pass formatted strings in shell.

The syntax looks like the following:

[COMMAND] <<[-] 'DELIMITER'
  HERE-DOCUMENT
DELIMITER

Using a - causes all leading tab characters to be ignored. This allows you to use indentation when writing heredocs.

If you quote the delimiter, the shell will not substitute variables.

cat << EOF
The current working directory is: $PWD
You are logged in as: $(whoami)
EOF

The output might be:

The current working directory is: /home/takashiidobe
You are logged in as: takashiidobe

You can redirect the output too, with << and >:

cat << EOF > file.txt
The current working directory is: $PWD
You are logged in as: $(whoami)
EOF

There heredoc can be piped as well:

cat <<'EOF' |  sed 's/l/e/g'
Hello
World
EOF

The output might look like:

Heeeo
Wored