cat << EOF

Examples of cat <<EOF syntax usage in Bash:

Some rules about the Here tags:

The tag can be any string, uppercase or lowercase, though most people use uppercase by convention.
The tag will not be considered as a Here tag if there are other words in that line. In this case, it will merely be considered part of the string. The tag should be by itself on a separate line, to be considered a tag.
The tag should have no leading or trailing spaces in that line to be considered a tag. Otherwise it will be considered as part of the string.

1. Assign multi-line string to a shell variable

$ sql=$(cat <<EOF
SELECT foo, bar FROM db
WHERE foo='baz'
EOF
)

The $sql variable now holds the new-line characters too. You can verify with echo -e "$sql".
2. Pass multi-line string to a file in Bash

$ cat <<EOF > print.sh
#!/bin/bash
echo \$PWD
echo $PWD
EOF

The print.sh file now contains:

#!/bin/bash
echo $PWD
echo /home/user

3. Pass multi-line string to a pipe in Bash

$ cat <<EOF | grep 'b' | tee b.txt
foo
bar
baz
EOF

4.

$ cat >> test <<HERE
> Hello world HERE <-- Not by itself on a separate line -> not considered end of string
> This is a test
> HERE <-- Leading space, so not considered end of string
> and a new line
> HERE <-- Now we have the end of the string

5.

cat <<EOF >>brightup.sh
#!/bin/sh
# Created on $(date # : <<-- this will be evaluated before cat;)
echo "\$HOME will not be evaluated because it is backslash-escaped"
EOF

2019-12-19 13:42:00

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