how to write in a file in shell code example

Example 1: bash write file

# syntax (note: the -e switch is to allow for backslash escapes)
# echo -e "<string-to-append>" >> <file-to-append-to>

# example 
echo -e "Hello there, new line!" >> RandomWorld.txt

# -----------------------------------------------
# In order to see the effect of -e, use the following string:
# "Hello there,\n new line!"

Example 2: write in a file linux

sudo apt-get update
sudo apt install nano
nano <filename>