gistfile1.none

            $text =~ s{ (?<!\\\n)        # not after line ending in '\'
                        ^                # beginning of line
                        (\t(?>@?)[ \t]*) # capture tab, optional @, and hspace
                        (?!-)            # not before - (ignore error) lines
                        (?!cd)           # not before cd lines
                        (?!echo)         # not before echo lines
                        (?=\S)           # must be before non-blank
                      }
                      { $1time\ }mgx;