"Here is number #123".gsub(/[a-z]/i, "#").gsub(/#/, "P")


puts "Here is number #123".gsub(/[a-z]/i, "#").gsub(/#/, "P")

1.	gsub does multiple substitutions at once
2.	gsub method that performs a global substitution (like a search and replace) upon the string
3.	use gsub to eradicate the spaces from text string
4.	Splitting Text into Sentences
5.	Testing Sentence Separation
6.	gsub (or gsub!) replaces a substring (first argument) with a replacement string (second argument)
7.	gsub alll with all
8.	gsub lll with ll
9.	Normalize Ruby source code by replacing tabs with spaces
10.	Transform Windows-style newlines to Unix-style newlines
11.	Use whitespace as the place holder
12.	"FOO bar".gsub(/foo/i, "The bar").gsub(/bar/m, "result")
13.	gsub(/[^\d]+/, '').split(//)

"Here is number #123".gsub(/[a-z]/i, "#").gsub(/#/, "P") : gsub « String « Ruby