I have a configuration script which does basically this:

```
#!/bin/bash

source vars.sh

cat >foo.output <<EOF
# some static stuff (many lines...)
variable_bit=($SOME_VAR, $SOME_OTHER_VAR, ...)
# some more static stuff (many lines...)
EOF

```

It would be nicer to have some other file, call it `foo.output.template`, which looked like this

```
# some static stuff (many lines...)
VARIABLE_BIT
# some more static stuff (many lines...)

```

Then, my configuration script could do something like this

```
sed 's/VARIABLE_BIT/<<STDIN>>/' foo.output.template >foo.output <<EOF
variable_bit=($SOME_VAR, $SOME_OTHER_VAR, ...)
EOF

```

This won't work, and I don't know if `sed` can do this, but the intention is that it

* reads foo.output.template
* matches `VARIABLE_BIT`
* replaces this with whatever is in stdin
* then pipes to foo.output

Can `sed`, `awk`, or some other common \*nix utility do this easily?