Using temporary pipes to run shell code from binary executables.

poc.sh

#!/bin/sh

###
# Uses the 3 pipe to run commands.
#
# In Rust: https://stackoverflow.com/a/54858159
##
inner()
{
    echo 'echo "Hello, before!"' >&3

    # If we don't sleep, printf may run before shell code above.
    sleep 0.1

    printf 'Name? '
    read -r NAME

    echo 'echo "Hello, '"$NAME"'!"' >&3
    echo break >&3
}

# Create the name for the pipe.
PIPE="$(mktemp -u)"

# Create the pipe.
mkfifo "$PIPE"

# Alias it to "3".
exec 3<>"$PIPE"

# Remove the actual file.
rm "$PIPE"

# Run a command that uses the pipe.
(inner 0<&0 &)

# Evaluate output from 3.
while read -r THIRD; do
    eval $THIRD
done <&3

# Wait for background task.
wait

# Close the pipe.
exec 3>&-