Replace one substring for another string in shell script

Question

I have "I love Suzi and Marry" and I want to change "Suzi" to "Sara".

#!/bin/bash firstString="I love Suzi and Marry" secondString="Sara" # do something... 

The result must be like this:

firstString="I love Sara and Marry" 

Answer 1

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".)

Note that this feature is not specified by POSIX — it's a Bash extension — so not all Unix shells implement it. For the relevant POSIX documentation, see The Open Group Technical Standard Base Specifications, Issue 7, the Shell & Utilities volume, §2.6.2 "Parameter Expansion".

Answer 2

This can be done entirely with bash string manipulation:

first="I love Suzy and Mary" second="Sara" first=${first/Suzy/$second} 

That will replace only the first occurrence; to replace them all, double the first slash:

first="Suzy, Suzy, Suzy" second="Sara" first=${first//Suzy/$second} # first is now "Sara, Sara, Sara"