Direct group of commands into `docker exec`

I have the following command that works fine and prints foo before returning:

docker exec -i <id> /bin/sh < echo "echo 'foo'"

I want to direct multiple commands into the container with one pipe, for example echo 'foo' and ls /. I have tried the following:

This fails because it runs the commands on the host and pipes the output into the container:
```
{
    echo "foo"
    ls /
} | docker exec -i <id> /bin/sh
```
This fails because it has bad syntax. It also runs on the host:
```
{
    echo "foo"
    ls /
} | docker exec -i <id> /bin/sh
```

This one fails, but I would like to not use an array of strings anyway:

for COMMAND in 'echo "foo"' 'ls /'
do
    docker exec -i <id> /bin/sh < echo $COMMAND
done

I've also tried several other methods like piping commands into tee or echo but haven't had any luck. If you would like to know why I want to do this seemingly ridiculous thing, it's because:

This is a short script that I would like to keep all in one place
I would like to use syntax highlighting, so I don't want to store it all in a list of strings
The container has the programs the script should run and the host does not
This is an automatic process that I would like to trigger with crontab on the host

Solution

Use a here document.

docker run -i --rm alpine /bin/sh <<EOF
echo abc
ls /
EOF

Note the difference between quoted and unquoted here document delimiter.

docker exec -i <id> /bin/sh < echo "echo 'foo'"

I think you meant to do:

docker exec -i <id> /bin/sh < <(echo "echo 'foo'")

which is just the same as:

docker exec -i <id> /bin/sh <<<"echo 'foo'"

@edit There is a cool little trick. The idea is to pipe the script itself except first lines to another subprocess, it's sometimes used by installer scripts:

#!/bin/sh
# output this script except first 4 lines to docker
tail -n+5 "$0" | docker run -i --rm alpine /bin/sh -x
exit  # we exit original script
#!/bin/sh
# inside docker now
echo abc
ls /

Execution:

$ bash -x ./script.sh
+ tail -n+5 ./script.sh
+ docker run -i --rm alpine /bin/sh -x
+ echo abc
+ ls /
abc
bin
...
var
+ exit

In a similar fashion you could use sed or another parsing tool to extract the only the relevant part between some marks for example.