run halbot directly without all the pre-existing crappy shell scripts. This neat little script runs your elixir app just from its name and std FreeBSD pkg layout

app.sh

#!/bin/sh -e
# obvious
export APP=$(basename -s .sh $0)

# derived paths are OS dependent
export ERTS=$(find /usr/local/lib/erlang -type d -depth 1 -name erts-\*)
export VERSION=$(cut -swf 2 /usr/local/lib/${APP}/releases/start_erl.data)

# config files
CONFIGS=/usr/local/etc/${APP}
export SYSCONFIG=${CONFIGS}/sys.config
export VMARGS=${CONFIGS}/vm.args

# custom parameters
export PORT=4003

# BEAM essentials
export LD_LIBRARY_PATH=${ERTS}/lib:
export BINDIR=${ERTS}/bin
export PATH=${BINDIR}:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
export ROOTDIR=/usr/local/lib
export PROGNAME=${ROOTDIR}/releases/${VERSION}/${APP}.sh
export ERL_LIBS=${ROOTDIR}/lib:/usr/local/erlang/lib

export MODE="-mode embedded"

# elixir
export LANG=en_US.UTF-8
export LC_ALL=en_US.UTF-8

# useful BEAM bits
# export ERL_AFLAGS="-kernel shell_history enabled"
# no turds on BEAM exit
export ERL_CRASH_DUMP=/dev/null
export ERL_CRASH_DUMP_BYTES=0
export ERL_CRASH_DUMP_SECONDS=0

# debug beam startup
# export VERBOSE="-init_debug "
# ensure epmd is managed by OS daemons and not tied to this app
export EPMD="-start_epmd false"
# keep user sticky fingers out of the console
# see http://erlang.org/doc/man/run_erl.html
# export RUN_ERL_DISABLE_FLOWCNTRL=1
# export DOTERL="-boot no_dot_erlang"

cd /usr/local/lib/${APP}

${BINDIR}/erlexec \
    ${VERBOSE} \
    ${DOTERL} \
    ${EPMD} \
    ${MODE} \
    -boot ${ROOTDIR}/releases/${VERSION}/${APP} \
    -boot_var ERTS_LIB_DIR ${ERTS}/../lib \
    -env ERL_LIBS ./rel/${APP}/lib \
    -pa ${ROOTDIR}/lib/${APP}-${VERSION}/consolidated \
    -pz ${ROOTDIR}/lib/${APP}-${VERSION}/ebin \
    -args_file ${VMARGS} \
    -config ${SYSCONFIG} \
    -user Elixir.IEx.CLI \
    -extra \
    --no-halt \
    +iex -- console