One liner to assume an AWS IAM role and set environment variables to use the resulting STS credentials

assume-role.bash

#!/bin/bash -x

# Session duration
# DURATION=43200
DURATION=3600

unset AWS_ACCESS_KEY_ID AWS_SECRET_ACCESS_KEY AWS_SESSION_TOKEN

if ! sts=( $(
  aws sts assume-role \
  --duration-seconds "$DURATION" \
  --role-arn $1 \
  --role-session-name gene \
  --query 'Credentials.[AccessKeyId,SecretAccessKey,SessionToken]' \
  --output text
) ); then
  exit 1
fi

echo "export AWS_ACCESS_KEY_ID=${sts[0]} AWS_SECRET_ACCESS_KEY=${sts[1]} AWS_SESSION_TOKEN=${sts[2]}"

how-to-call.bash

$(assume-role.bash arn:aws:iam::123456789012:role/example-role)