bash echo replace line code example

Example 1: bash script: replace . with :

#To replace the first occurrence of a pattern with a given string,
#use ${parameter/pattern/string}:

#!/bin/bash
firstString="I love Suzi and Marry"
secondString="Sara"
echo "${firstString/Suzi/$secondString}"    

# prints 'I love Sara and Marry'

#To replace all occurrences, use ${parameter//pattern/string}:

message='The secret code is 12345'
echo "${message//[0-9]/X}"           
# prints 'The secret code is XXXXX'


#(This is documented in the Bash Reference Manual, §3.5.3 "Shell Parameter Expansion".)

Example 2: bash replace comma with newline

Just use tr command as follow:
tr , '\n' < file	#Replaces all ',' matches for a new line