s6-overlay/builder/overlay-rootfs/usr/bin/printcontenv

#!/bin/execlineb -S0

# test if arguments were given
if { s6-test ${#} -ge 1 }

importas -D 0 S6_KEEP_ENV S6_KEEP_ENV
# if S6_KEEP_ENV was passed, whole supervision tree should see
# original docker environement
ifelse  { s6-test ${S6_KEEP_ENV} -ne 0 }
{
  redirfd -w 2 /dev/null importas -i value ${1}
  s6-echo -n -- ${value}
}

# else: original docker env was dumped into container_environment
# retrieve it from there and print if it exists
if { s6-test -f /var/run/s6/container_environment/${1} }
if 
{
  backtick value
  {
    redirfd -r 0 /var/run/s6/container_environment/${1}
    s6-cat
  }
  importas -u value value
  s6-echo -- ${value}
}