sed line selects sequences of chars and replace them with
". The parts of the line which are not matched are left unchanged.
\| means or, so it separates 2 regexes.
Any sequence of chars matched by these 2 regexes is replaced with
The first is
^. It matches the start of the line.
If start of the line is encountered, it is replaced with
The second regex is
: *broken symbolic.*$: it means any string starting with
: and zero or any number of space chars (
broken symbolic char sequence, and followed with
.* which means zero or any number of any chars, up to the end of line
$. If encountered it is replaced with
lred_6607 is not matched at all, so it is left unchanged.
The result is