Sed regex and substring negation

Question

What is the correct syntax for finding a substring (a string which is preceded and followed by specific strings) which does not match a specific pattern?

Answer 1

This might work for you:

sed 'h;s/BEGIN_\(.*\)_END/(\1)/;/^(FOO)$/g' file

This only works if there is only one string per line.

For multiple strings per line:

sed 's/BEGIN_\([^F][^_]*\|F[^O][^_]*\|FO[^O][^_]*\|FOO[^_]\+\)_END/\(\1\)/g' file

Or the more easily understood:

sed 's/\(BEGIN_\)FOO\(_END\)/\1\n\2/g;s/BEGIN_\([^\n_]*\)_END/(\1\)/g;s/\n/FOO/g' file