! s/^\s*:\s*// && $s
s/^\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
-s switch was used to invoke
psh. So, the
entire expression is true if the command did not begin with a colon and
-s switch was given.
-sswitch 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.