An example of setting a custom environment variable already defined in the container

Singularity

Bootstrap: docker
From: centos:7

# sudo singularity build lamps.simg Singularity
%environment

now=`date '+%Y_%m_%d'`
hostname=`hostname`

APPNAME="lammps"
RESULTS_DIR=${HOME}/${APPNAME}
LOG="${hostname}_${APPNAME}_${now}"
RESULTS="${hostname}_${APPNAME}_${now}.results"
SYSCONFIG="${hostname}_${APPNAME}_${now}.sysconfig"
APPINFO="${hostname}_${APPNAME}_${now}.appinfo"
export APPNAME LOG RESULTS SYSCONFIG APPINFO now hostname RESULTS_DIR

%apprun lammps

echo "${SCIF_APPNAME} is running."
WORKDIR=${SCIF_APPROOT}

if [ -n "$CUSTOM_RESULTS_DIR" ]; then
    RESULTS_DIR=$CUSTOM_RESULTS_DIR
else
    RESULTS_DIR=${HOME}/${APPNAME}
fi

if [ ! -x "$RESULTS_DIR" ]; then
  mkdir -p $RESULTS_DIR
fi

cd $WORKDIR
echo "Single node Output file is $RESULTS and log is $LOG and results dir is $RESULTS_DIR" |tee $RESULTS_DIR/$RESULTS

%post
yum install -y sudo wget vi which
yum install -y hostname lscpu uptime redhat-lsb