extract substring by regex from a text file

[Alessio]

Hi,

I'm facing the problem in the subject:
- I have a text file that I need to parse for producing a specifical
string (Json like) extracting some information (substring) in it;
- I created regural expressions capable to locate these substrings in
my txt file;

now I don't know how to continue. What is the best way to locate some
string in a file and output them (with print command or in another
file)?

Thx in advance