how to set environment variable in terminal linux code example

Example 1: linux set environment

# syntax 
# setenv SHELL *<filepath-of-file-containing-environment-settings>

# example
setenv SHELL /usr/bin/bash

Example 2: linux set environment variable

# Linux - Bash 

# syntax 
# export *<variable-name>=*<variable-value>;

# example 
export ORACLE_SID='sales_database';