string="stirng" ; echo "${string//ir/ri}"

echo [string] | sed "s/[original]/[target]/g"

#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".)

string="abc"

final=${string//[a]/b}

​

echo $final

#!/bin/bash

firstString="I love Suzi and Marry"

secondString="Sara"

echo "${firstString/Suzi/$secondString}"    

# prints 'I love Sara and Marry'

​

string="x + x + y = 3y"

echo $string | sed 's/x/y/g'

​

# Result: y + y + y = 3y

​

# Breakdown:

# Pass echo result ("pipe") into sed which substitudes x with y.

# Sed Usage: sed '<option: substitute>/<delimeter>/<replacement>/<scale: global>

#1) Open the file in vi or vim

#2) Run the replacement command in vi (or vim) as follows

​

# Replace all matching patterns

:s%/PatternToReplace/Replacement

​

# Replace one matching pattern at a time

:s/PatternToReplace/Replacement