bash run script from here doc [duplicate]

Question

In the code below, variable X is output normally.

# cat a.sh X=world echo 'hello' $X # cat a.sh | bash hello world

But, using here doc, variable X is not displayed.

# cat <<EOF | bash > X=world > echo 'hello' $X > EOF hello # bash -s <<EOF > X=world > echo 'hello' $X > EOF hello

What made this difference?

The opposite problem (but the answer should still help you): stackoverflow.com/questions/4937792/… — melpomene
– melpomene, Commented Mar 16, 2019 at 9:23

Walter A · Accepted Answer · 2019-03-16 09:56:29Z

You can see what happens when you remove the |bash

X=oldvalue cat <<EOF X=world echo "hello $X" EOF

The $X is replaced before piping it to bash.
You can check the following

X=oldvalue cat <<"EOF" X=world echo "hello $X" EOF

This is what you want to execute:

cat <<"EOF" | bash X=world echo "hello $X" EOF

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