Ah, I misread that part of the specification.

Most likely, the easiest approach is now to do replacement with /e and look-ahead and look-behind:

# Expand string to the left
$string4 =~ s!(?<=N)(-+)(?=B)!'B' x length $1!e;

# Expand string to the right
$string4 =~ s!(?<=B)(-+)!'B' x length $1!e;

[download]

In reply to Re^5: How can I expand my substring? by Corion
in thread How can I expand my substring? by Anonymous Monk

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