Writing multi-line text to a file in BASH

In writing bash scripts, you often need to write multi-line configuration files. Here are some ways to do this.

source: https://stackoverflow.com/questions/11162406/open-and-write-data-to-text-file-using-bash

#!/bin/bash

# Use echo to redirect text to a file.
echo "some data for the file" >> fileName

#----------------------------------------------------------
# Use various redirections
cat > FILE.txt <<EOF
info code info 
info code info
info code info
EOF 

#----------------------------------------------------------
# Open file descriptor (fd) 3 for read/write on a text file.
exec 3<> poem.txt

    # Let's print some text to fd 3
    echo "Roses are red" >&3
    echo "Violets are blue" >&3
    echo "Poems are cute" >&3
    echo "And so are you" >&3

# Close fd 3
exec 3>&-
cat poem.txt

#----------------------------------------------------------
# If you need to do this with root privileges, do it this way:
sudo sh -c 'echo "some data for the file" >> fileName'

#----------------------------------------------------------
# If you are using variables, you can use:
first_var="Hello"
second_var="How are you"
echo "${first_var} - ${second_var}" > ./file_name.txt