Well, at least one of the approaches is incorrect. I uncommented the warnings, turned them into prints and added the following to your program: 
dosubstr;
print "---\n";
doregex;

[download]
Running your program gives me: 
A12345 RELEASE 
  
A1 2345RELEASEA12345 
FTOP DD_BUIL+ 
  
FT OPDD_REKL+FTOP 
FTOP DD_PLAN+ 
  
FT OPDD_REKL+FTOP 
---

[download]

Abigail

In reply to Re: fast string parser: regex versus substr by Abigail-II
in thread fast string parser: regex versus substr by mce

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