Run this script with a tnsnames.ora file as the only parameter to install instantclient version 12.2.0.1.0-2 (once you have downloaded the files from Oracle of course).

install-sqlplus.bash

#!/usr/bin/env bash
## https://oraclespin.com/2018/01/25/install-sqlplus-instant-client-on-macos/
VERSION="12.2.0.1.0-2"
FILES="instantclient-basic-macos.x64-$VERSION.zip instantclient-sqlplus-macos.x64-$VERSION.zip instantclient-sdk-macos.x64-$VERSION.zip"
INSTALL_DIR="instantclient_12_2"

if [ $# -lt 1 ]; then
    echo "Specify tnsnames.ora location"
    exit 1
fi

TNSNAMES=$1

function clean() {
    echo "Cleaning up..."
    for f in $FILES; do
      if [ ! -f $f ]; then
        echo "Missing file $f"
        exit 1
      fi
    done
    if [ -d $HOME/$INSTALL_DIR ]; then
      rm -rf $HOME/$INSTALL_DIR
    fi
    if [ -d $INSTALL_DIR ]; then
      rm -rf $INSTALL_DIR
    fi
    if [ -f /usr/local/lib/libclntsh.dylib ]; then
        sudo rm /usr/local/lib/libclntsh.dylib
    fi
    if [ -f /usr/local/lib/libclntsh.dylib.12.1 ]; then
        sudo rm /usr/local/lib/libclntsh.dylib.12.1
    fi
    echo "Done."
}

clean

unzip instantclient-basic-macos.x64-$VERSION.zip
cd instantclient_12_2 && unzip -j ../instantclient-sqlplus-macos.x64-$VERSION.zip && cd ..

mv $INSTALL_DIR $HOME
mkdir -p $HOME/instantclient_12_2/network/admin

sudo ln -s ~/instantclient_12_2/libclntsh.dylib /usr/local/lib/
sudo ln -s ~/instantclient_12_2/libclntsh.dylib.12.1 /usr/local/lib/
ls -l /usr/local/lib/ | grep $HOME

export PATH=$HOME/instantclient_12_2:$PATH

export TNS_ADMIN=$HOME/instantclient_12_2/network/admin

cd $TNS_ADMIN

cp $TNSNAMES .

export ORACLE_HOME=$HOME/$INSTALL_DIR
export DYLD_LIBRARY_PATH=$ORACLE_HOME