! s/^\s*:\s*// && $ss/^\s*:\s*//) tries
to match $_ against this pattern: the beginning of the
string (^) followed by zero or more whitespace characters
(\s*), then a colon (:), then possibly some more
whitespace (\s*). If it matches, the matching part of the
string is stripped out (ie, substituted with nothing) and the substitute
expression has a true value. If not, it just has a false value.
The negate operator (!) then reverses the truth value
of the substitute expression. So, the left side of the "and"
(&&) expression is true if the command did not
begin with a colon.
The right side of the expression ($s), indicates whether
the -s switch was used to invoke psh. So, the
entire expression is true if the command did not begin with a colon and
the -s switch was given.
Note:
-s switch wasn't
given, the colon still will be stripped off.
s///) are true if the
substitute pattern applied and was performed and false if they
weren't.