Here documents (heredoc) tips

cat <<EOF > config.props
url=http://stack1.com
component=123
name=config
timeout=10
EOF

Creates config.props with the contents:
url=http://stack1.com
component=123
name=config
timeout=10

tr [a-z] [A-Z] << EOF
The cat sat on the mat
The cow jumped over the moon
EOF

Gives the output:
THE CAT SAT ON THE MAT
THE COW JUMPED OVER THE MOON

 

cat << END_TEXT | awk '{print $3 " " $2 " " $1}'
one two three 
three two one
END_TEXT

Gives the output:
three two one
one two three

 

cat <<EOF | kubectl create -f -
apiVersion: v1
kind: Pod
metadata:
  name: test-pod
spec:
  containers:
    - name: test-container
      image: k8s.gcr.io/busybox
      command: [ "/bin/sh", "-c", "env" ]
      envFrom:
      - configMapRef:
          name: env-config
  restartPolicy: Never
EOF

Creates a kubernetes busybox Pod

 

Using heredocs with sudo

example 1:

sudo bash -c "cat >> /etc/hosts" << "EOF"
10.0.1.100  ansible
10.0.1.101  kube_controller
10.0.1.102  kube_node_1
10.0.1.103  kube_node_2
10.0.1.104  kube_node_3
EOF

example 2:

cat <<EOF | sudo tee /etc/yum.repos.d/influxdb.repo
[influxdb]
name = InfluxDB Repository - RHEL \$releasever
baseurl = https://repos.influxdata.com/rhel/\$releasever/\$basearch/stable
enabled = 1
gpgcheck = 1
gpgkey = https://repos.influxdata.com/influxdb.key
EOF